Merge of dataspace improvements from develop.

1 files changed, 5600 insertions, 3979 deletions

diff --git a/src/H5Shyper.c b/src/H5Shyper.c
index af9e3bc..42b9acd 100644
--- a/src/H5Shyper.c
+++ b/src/H5Shyper.c
@@ -12,7 +12,7 @@
  * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * */
 
 /*
- * Programmer:  Quincey Koziol <koziol@ncsa.uiuc.edu>
+ * Programmer:  Quincey Koziol
  *              Thursday, June 18, 1998
  *
  * Purpose:     Hyperslab selection dataspace I/O functions.
@@ -37,56 +37,138 @@
 #include "H5Spkg.h"             /* Dataspace functions                      */
 #include "H5VMprivate.h"        /* Vector functions                         */
 
-/* Format version bounds for dataspace hyperslab selection */
-const unsigned H5O_sds_hyper_ver_bounds[] = {
-    H5S_HYPER_VERSION_1,    /* H5F_LIBVER_EARLIEST */
-    H5S_HYPER_VERSION_1,    /* H5F_LIBVER_V18 */
-    H5S_HYPER_VERSION_2     /* H5F_LIBVER_LATEST */
-};
 
 /****************/
 /* Local Macros */
 /****************/
 
+/* Flags for which hyperslab fragments to compute */
+#define H5S_HYPER_COMPUTE_B_NOT_A 0x01
+#define H5S_HYPER_COMPUTE_A_AND_B 0x02
+#define H5S_HYPER_COMPUTE_A_NOT_B 0x04
+
+/* Macro to advance a span, possibly recycling it first */
+#define H5S_HYPER_ADVANCE_SPAN(recover, curr_span, next_span)   \
+    do {                                                        \
+        H5S_hyper_span_t *saved_next_span = (next_span);        \
+                                                                \
+        /* Check if the span should be recovered */             \
+        if(recover) {                                           \
+            H5S__hyper_free_span(curr_span);                    \
+            (recover) = FALSE;                                  \
+        } /* end if */                                          \
+                                                                \
+        /* Set the current span to saved next span */           \
+        (curr_span) = saved_next_span;                          \
+    } while(0)
+
+/* Macro to add "skipped" elements to projection during the execution of
+ * H5S__hyper_project_intersect() */
+#define H5S_HYPER_PROJ_INT_ADD_SKIP(UDATA, ADD, ERR)            \
+    do {                                                        \
+        /* If there are any elements to add, we must add them   \
+         * to the projection first before adding skip */        \
+        if((UDATA)->nelem > 0)                                  \
+            if(H5S__hyper_proj_int_build_proj(UDATA) < 0)       \
+                HGOTO_ERROR(H5E_DATASPACE, H5E_CANTAPPEND, ERR, "can't add elements to projected selection") \
+        (UDATA)->skip += (ADD);                                 \
+    } while(0) /* end H5S_HYPER_PROJ_INT_ADD_SKIP() */
+
 
 /******************/
 /* Local Typedefs */
 /******************/
 
+/* Define alias for hsize_t, for allocating H5S_hyper_span_info_t + bounds objects */
+/* (Makes it easier to understand the alloc / free calls) */
+typedef hsize_t hbounds_t;
+
+/* Struct for holding persistent information during iteration for
+ * H5S__hyper_project_intersect() */
+typedef struct {
+    const H5S_hyper_span_t *ds_span[H5S_MAX_RANK]; /* Array of the current spans in the destination space in each dimension */
+    hsize_t ds_low[H5S_MAX_RANK]; /* Array of current low bounds (of iteration) for each element in ds_span */
+    H5S_hyper_span_info_t *ps_span_info[H5S_MAX_RANK]; /* Array of span info structs for projected space during iteration */
+    uint32_t  ps_clean_bitmap; /* Bitmap of whether the nth rank has a clean projected space since the last time it was set to 1 */
+    unsigned ss_rank;       /* Rank of source space */
+    unsigned ds_rank;       /* Rank of destination space */
+    unsigned depth;         /* Current depth of iterator in destination space */
+    hsize_t skip;           /* Number of elements to skip in projected space */
+    hsize_t nelem;          /* Number of elements to add to projected space (after skip) */
+    uint64_t op_gen;        /* Operation generation for counting elements */
+    hbool_t share_selection; /* Whether span trees in dst_space can be shared with proj_space */
+} H5S_hyper_project_intersect_ud_t;
+
+/* Assert that H5S_MAX_RANK is <= 32 so our trick with using a 32 bit bitmap
+ * (ps_clean_bitmap) works.  If H5S_MAX_RANK increases either increase the size
+ * of ps_clean_bitmap or change the algorithm to use an array. */
+#if H5S_MAX_RANK > 32
+#error H5S_MAX_RANK too large for ps_clean_bitmap field in H5S_hyper_project_intersect_ud_t struct
+#endif
+
+
 /********************/
 /* Local Prototypes */
 /********************/
 static H5S_hyper_span_t *H5S__hyper_new_span(hsize_t low, hsize_t high,
     H5S_hyper_span_info_t *down, H5S_hyper_span_t *next);
-static herr_t H5S__hyper_span_precompute(H5S_hyper_span_info_t *spans, size_t elmt_size);
-static void H5S__hyper_span_scratch(H5S_hyper_span_info_t *spans);
-static H5S_hyper_span_info_t *H5S__hyper_copy_span(H5S_hyper_span_info_t *spans);
+static H5S_hyper_span_info_t *H5S__hyper_new_span_info(unsigned rank);
+static H5S_hyper_span_info_t *H5S__hyper_copy_span_helper(
+    H5S_hyper_span_info_t *spans, unsigned rank, unsigned op_info_i,
+    uint64_t op_gen);
+static H5S_hyper_span_info_t *H5S__hyper_copy_span(H5S_hyper_span_info_t *spans,
+    unsigned rank);
 static hbool_t H5S__hyper_cmp_spans(const H5S_hyper_span_info_t *span_info1,
     const H5S_hyper_span_info_t *span_info2);
-static herr_t H5S__hyper_free_span_info(H5S_hyper_span_info_t *span_info);
-static herr_t H5S__hyper_free_span(H5S_hyper_span_t *span);
-static hbool_t H5S__hyper_is_valid_helper(const H5S_hyper_span_info_t *spans,
-    const hssize_t *offset, const hsize_t *size);
-static herr_t H5S__hyper_recover_span(hbool_t *recover,
-    H5S_hyper_span_t **curr_span, H5S_hyper_span_t *next_span);
-static H5S_hyper_span_t *H5S__hyper_coord_to_span(unsigned rank,
-    const hsize_t *coords);
-static herr_t H5S__hyper_append_span(H5S_hyper_span_t **prev_span,
-    H5S_hyper_span_info_t **span_tree, hsize_t low, hsize_t high,
-    H5S_hyper_span_info_t *down, H5S_hyper_span_t *next);
+static void H5S__hyper_free_span_info(H5S_hyper_span_info_t *span_info);
+static void H5S__hyper_free_span(H5S_hyper_span_t *span);
+static herr_t H5S__hyper_span_blocklist(const H5S_hyper_span_info_t *spans,
+    hsize_t start[], hsize_t end[], hsize_t rank, hsize_t *startblock, hsize_t *numblocks,
+    hsize_t **buf);
+static herr_t H5S__get_select_hyper_blocklist(H5S_t *space, hsize_t startblock,
+    hsize_t numblocks, hsize_t *buf);
+static H5S_hyper_span_t *H5S__hyper_coord_to_span(unsigned rank, const hsize_t *coords);
+static herr_t H5S__hyper_append_span(H5S_hyper_span_info_t **span_tree,
+    unsigned ndims, hsize_t low, hsize_t high, H5S_hyper_span_info_t *down);
 static herr_t H5S__hyper_clip_spans(H5S_hyper_span_info_t *a_spans,
-    H5S_hyper_span_info_t *b_spans, H5S_hyper_span_info_t **a_not_b,
+    H5S_hyper_span_info_t *b_spans, unsigned selector,
+    unsigned ndims, H5S_hyper_span_info_t **a_not_b,
     H5S_hyper_span_info_t **a_and_b, H5S_hyper_span_info_t **b_not_a);
-static herr_t H5S__hyper_merge_spans(H5S_t *space,
-    H5S_hyper_span_info_t *new_spans, hbool_t can_own);
-static hsize_t H5S__hyper_spans_nelem(const H5S_hyper_span_info_t *spans);
+static herr_t H5S__hyper_merge_spans(H5S_t *space, H5S_hyper_span_info_t *new_spans);
+static hsize_t H5S__hyper_spans_nelem_helper(H5S_hyper_span_info_t *spans,
+    unsigned op_info_i, uint64_t op_gen);
+static hsize_t H5S__hyper_spans_nelem(H5S_hyper_span_info_t *spans);
+static herr_t H5S__hyper_add_disjoint_spans(H5S_t *space, H5S_hyper_span_info_t *new_spans);
 static H5S_hyper_span_info_t *H5S__hyper_make_spans(unsigned rank,
-    const hsize_t *start, const hsize_t *stride, const hsize_t *count,
-    const hsize_t *block);
+    const hsize_t *start, const hsize_t *stride,
+    const hsize_t *count, const hsize_t *block);
+static herr_t H5S__hyper_update_diminfo(H5S_t *space, H5S_seloper_t op,
+    const H5S_hyper_dim_t *new_hyper_diminfo);
 static herr_t H5S__hyper_generate_spans(H5S_t *space);
+static hbool_t H5S__check_spans_overlap(const H5S_hyper_span_info_t *spans1,
+    const H5S_hyper_span_info_t *spans2);
+static herr_t H5S__fill_in_new_space(H5S_t *space1, H5S_seloper_t op,
+    H5S_hyper_span_info_t *space2_span_lst, hbool_t can_own_span2,
+    hbool_t *span2_owned, hbool_t *updated_spans, H5S_t **result);
 static herr_t H5S__generate_hyperslab(H5S_t *space, H5S_seloper_t op,
     const hsize_t start[], const hsize_t stride[], const hsize_t count[],
     const hsize_t block[]);
+static herr_t H5S__set_regular_hyperslab(H5S_t *space, const hsize_t start[],
+    const hsize_t *app_stride, const hsize_t app_count[], const hsize_t *app_block,
+    const hsize_t *opt_stride, const hsize_t opt_count[], const hsize_t *opt_block);
+static herr_t H5S__fill_in_select(H5S_t *space1, H5S_seloper_t op, H5S_t *space2,
+    H5S_t **result);
+static H5S_t *H5S__combine_select(H5S_t *space1, H5S_seloper_t op, H5S_t *space2);
+static herr_t H5S__hyper_iter_get_seq_list_gen(H5S_sel_iter_t *iter, size_t maxseq,
+    size_t maxelem, size_t *nseq, size_t *nelem, hsize_t *off, size_t *len);
+static herr_t H5S__hyper_iter_get_seq_list_opt(H5S_sel_iter_t *iter, size_t maxseq,
+    size_t maxelem, size_t *nseq, size_t *nelem, hsize_t *off, size_t *len);
+static herr_t H5S__hyper_iter_get_seq_list_single(H5S_sel_iter_t *iter, size_t maxseq,
+    size_t maxelem, size_t *nseq, size_t *nelem, hsize_t *off, size_t *len);
+static herr_t H5S__hyper_proj_int_build_proj(H5S_hyper_project_intersect_ud_t *udata);
+static herr_t H5S__hyper_proj_int_iterate(const H5S_hyper_span_info_t *ss_span_info,
+    const H5S_hyper_span_info_t *sis_span_info, hsize_t count, unsigned depth,
+    H5S_hyper_project_intersect_ud_t *udata);
 static void H5S__hyper_get_clip_diminfo(hsize_t start, hsize_t stride,
     hsize_t *count, hsize_t *block, hsize_t clip_size);
 static hsize_t H5S__hyper_get_clip_extent_real(const H5S_t *clip_space,
@@ -94,11 +176,9 @@ static hsize_t H5S__hyper_get_clip_extent_real(const H5S_t *clip_space,
 
 /* Selection callbacks */
 static herr_t H5S__hyper_copy(H5S_t *dst, const H5S_t *src, hbool_t share_selection);
-static herr_t H5S__hyper_get_seq_list(const H5S_t *space, unsigned flags,
-    H5S_sel_iter_t *iter, size_t maxseq, size_t maxbytes,
-    size_t *nseq, size_t *nbytes, hsize_t *off, size_t *len);
 static herr_t H5S__hyper_release(H5S_t *space);
 static htri_t H5S__hyper_is_valid(const H5S_t *space);
+static hsize_t H5S__hyper_span_nblocks(H5S_hyper_span_info_t *spans);
 static hssize_t H5S__hyper_serial_size(const H5S_t *space);
 static herr_t H5S__hyper_serialize(const H5S_t *space, uint8_t **p);
 static herr_t H5S__hyper_deserialize(H5S_t **space, const uint8_t **p);
@@ -110,7 +190,11 @@ static herr_t H5S__hyper_num_elem_non_unlim(const H5S_t *space,
 static htri_t H5S__hyper_is_contiguous(const H5S_t *space);
 static htri_t H5S__hyper_is_single(const H5S_t *space);
 static htri_t H5S__hyper_is_regular(const H5S_t *space);
+static htri_t H5S__hyper_shape_same(const H5S_t *space1, const H5S_t *space2);
+static htri_t H5S__hyper_intersect_block(const H5S_t *space, const hsize_t *start,
+    const hsize_t *end);
 static herr_t H5S__hyper_adjust_u(H5S_t *space, const hsize_t *offset);
+static herr_t H5S__hyper_adjust_s(H5S_t *space, const hssize_t *offset);
 static herr_t H5S__hyper_project_scalar(const H5S_t *space, hsize_t *offset);
 static herr_t H5S__hyper_project_simple(const H5S_t *space, H5S_t *new_space, hsize_t *offset);
 static herr_t H5S__hyper_iter_init(const H5S_t *space, H5S_sel_iter_t *iter);
@@ -122,11 +206,9 @@ static hsize_t H5S__hyper_iter_nelmts(const H5S_sel_iter_t *iter);
 static htri_t H5S__hyper_iter_has_next_block(const H5S_sel_iter_t *sel_iter);
 static herr_t H5S__hyper_iter_next(H5S_sel_iter_t *sel_iter, size_t nelem);
 static herr_t H5S__hyper_iter_next_block(H5S_sel_iter_t *sel_iter);
+static herr_t H5S__hyper_iter_get_seq_list(H5S_sel_iter_t *iter, size_t maxseq,
+    size_t maxbytes, size_t *nseq, size_t *nbytes, hsize_t *off, size_t *len);
 static herr_t H5S__hyper_iter_release(H5S_sel_iter_t *sel_iter);
-/* Static function for optimizing hyperslab */
-static hbool_t H5S__hyper_rebuild_helper(const H5S_hyper_span_t *span,
-    H5S_hyper_dim_t span_slab_info[], unsigned rank);
-static hbool_t H5S__hyper_rebuild(H5S_t *space);
 
 
 /*****************************/
@@ -144,7 +226,6 @@ const H5S_select_class_t H5S_sel_hyper[1] = {{
 
     /* Methods on selection */
     H5S__hyper_copy,
-    H5S__hyper_get_seq_list,
     H5S__hyper_release,
     H5S__hyper_is_valid,
     H5S__hyper_serial_size,
@@ -157,12 +238,26 @@ const H5S_select_class_t H5S_sel_hyper[1] = {{
     H5S__hyper_is_contiguous,
     H5S__hyper_is_single,
     H5S__hyper_is_regular,
+    H5S__hyper_shape_same,
+    H5S__hyper_intersect_block,
     H5S__hyper_adjust_u,
+    H5S__hyper_adjust_s,
     H5S__hyper_project_scalar,
     H5S__hyper_project_simple,
     H5S__hyper_iter_init,
 }};
 
+/* Format version bounds for dataspace hyperslab selection */
+const unsigned H5O_sds_hyper_ver_bounds[] = {
+    H5S_HYPER_VERSION_1,    /* H5F_LIBVER_EARLIEST */
+    H5S_HYPER_VERSION_1,    /* H5F_LIBVER_V18 */
+    H5S_HYPER_VERSION_2     /* H5F_LIBVER_LATEST */
+};
+
+/*******************/
+/* Local Variables */
+/*******************/
+
 /* Iteration properties for hyperslab selections */
 static const H5S_sel_iter_class_t H5S_sel_iter_hyper[1] = {{
     H5S_SEL_HYPERSLABS,
@@ -174,6 +269,7 @@ static const H5S_sel_iter_class_t H5S_sel_iter_hyper[1] = {{
     H5S__hyper_iter_has_next_block,
     H5S__hyper_iter_next,
     H5S__hyper_iter_next_block,
+    H5S__hyper_iter_get_seq_list,
     H5S__hyper_iter_release,
 }};
 
@@ -195,12 +291,17 @@ H5FL_DEFINE_STATIC(H5S_hyper_sel_t);
 /* Declare a free list to manage the H5S_hyper_span_t struct */
 H5FL_DEFINE_STATIC(H5S_hyper_span_t);
 
-/* Declare a free list to manage the H5S_hyper_span_info_t struct */
-H5FL_DEFINE_STATIC(H5S_hyper_span_info_t);
+/* Declare a free list to manage the H5S_hyper_span_info_t + hsize_t array struct */
+H5FL_BARR_DEFINE_STATIC(H5S_hyper_span_info_t, hbounds_t, H5S_MAX_RANK * 2);
 
 /* Declare extern free list to manage the H5S_sel_iter_t struct */
 H5FL_EXTERN(H5S_sel_iter_t);
 
+/* Current operation generation */
+/* (Start with '1' to avoid clashing with '0' value in newly allocated structs) */
+static uint64_t H5S_hyper_op_gen_g = 1;
+
+
 /* Uncomment this to provide the debugging routines for printing selection info */
 /* #define H5S_HYPER_DEBUG */
 #ifdef H5S_HYPER_DEBUG
@@ -210,9 +311,9 @@ H5S__hyper_print_spans_helper(FILE *f, const H5S_hyper_span_t *span, unsigned de
     FUNC_ENTER_STATIC_NOERR
 
     while(span) {
-        HDfprintf(f,"%s: depth=%u, span=%p, (%Hu, %Hu), nelem=%Hu, pstride=%Hu\n", FUNC, depth, span, span->low, span->high, span->nelem, span->pstride);
-        if(span->down && span->down->head) {
-            HDfprintf(f,"%s: spans=%p, count=%u, scratch=%p, head=%p\n", FUNC, span->down, span->down->count, span->down->scratch, span->down->head);
+        HDfprintf(f,"%s: %*sdepth=%u, span=%p, (%Hu, %Hu), next=%p\n", FUNC, depth * 2, "", depth, span, span->low, span->high, span->next);
+        if(span->down) {
+            HDfprintf(f,"%s: %*sspans=%p, count=%u, bounds[0]={%Hu, %Hu}, head=%p\n", FUNC, (depth + 1) * 2, "", span->down, span->down->count, span->down->low_bounds[0], span->down->high_bounds[0], span->down->head);
             H5S__hyper_print_spans_helper(f, span->down->head, depth + 1);
         } /* end if */
         span = span->next;
@@ -227,7 +328,7 @@ H5S__hyper_print_spans(FILE *f, const H5S_hyper_span_info_t *span_lst)
     FUNC_ENTER_STATIC_NOERR
 
     if(span_lst != NULL) {
-        HDfprintf(f, "%s: spans=%p, count=%u, scratch=%p, head=%p\n", FUNC, span_lst, span_lst->count, span_lst->scratch, span_lst->head);
+        HDfprintf(f, "%s: spans=%p, count=%u, bounds[0]={%Hu, %Hu}, head=%p\n", FUNC, span_lst, span_lst->count, span_lst->low_bounds[0], span_lst->high_bounds[0], span_lst->head);
         H5S__hyper_print_spans_helper(f, span_lst->head, 0);
     } /* end if */
 
@@ -281,10 +382,179 @@ H5S__hyper_print_diminfo(FILE *f, const H5S_t *space)
 
     FUNC_LEAVE_NOAPI(SUCCEED)
 }
+
+
+/*--------------------------------------------------------------------------
+ NAME
+    H5S__hyper_print_spans_dfs
+ PURPOSE
+    Output the span elements for one span list in depth-first order
+ USAGE
+    herr_t H5S__hyper_print_spans_dfs(f, span_lst, depth)
+        FILE *f;                                  IN: the file to output
+        const H5S_hyper_span_info_t *span_lst;    IN: the span list to output
+        unsigned depth;                           IN: the level of this span list
+ RETURNS
+    non-negative on success, negative on failure
+ GLOBAL VARIABLES
+ COMMENTS, BUGS, ASSUMPTIONS
+ EXAMPLES
+ REVISION LOG
+--------------------------------------------------------------------------*/
+static herr_t
+H5S__hyper_print_spans_dfs(FILE *f, const H5S_hyper_span_info_t *span_lst,
+    unsigned depth, unsigned dims)
+{
+    H5S_hyper_span_t *actual_tail = NULL;
+    H5S_hyper_span_t *cur_elem;
+    unsigned num_elems = 0;
+    unsigned u, elem_idx;
+
+    FUNC_ENTER_STATIC_NOERR
+
+    /* get the actual tail from head */
+    cur_elem = span_lst->head;
+    HDassert(cur_elem); /* at least 1 element */
+    while(cur_elem) {
+        actual_tail = cur_elem;
+        cur_elem = cur_elem->next;
+        num_elems++;
+    } /* end while */
+
+    for(u = 0; u < depth; u++)
+        HDfprintf(f, "\t");
+    HDfprintf(f, "DIM[%u]: ref_count=%u, #elems=%u, head=%p, tail=%p, actual_tail=%p, matched=%t\n", depth,
+              span_lst->count, num_elems, span_lst->head,
+              span_lst->tail, actual_tail, (span_lst->tail == actual_tail));
+
+    for(u = 0; u < depth; u++)
+        HDfprintf(f, "\t");
+    HDfprintf(f, "low_bounds=[");
+    for(u = 0; u < dims - 1; u++)
+        HDfprintf(f, "%llu,", span_lst->low_bounds[u]);
+    HDfprintf(f, "%llu]\n", span_lst->low_bounds[dims - 1]);
+
+    for(u = 0; u < depth; u++)
+        HDfprintf(f, "\t");
+    HDfprintf(f, "high_bounds=[");
+    for(u = 0; u < dims - 1; u++)
+        HDfprintf(f, "%llu,", span_lst->high_bounds[u]);
+    HDfprintf(f, "%llu]\n", span_lst->high_bounds[dims - 1]);
+
+    cur_elem = span_lst->head;
+    elem_idx = 0;
+    while(cur_elem) {
+        for(u = 0; u < depth; u++)
+            HDfprintf(f, "\t");
+        HDfprintf(f, "ELEM[%u]: ptr=%p, low=%Hu, high=%Hu, down=%p\n",
+                  elem_idx++, cur_elem, cur_elem->low, cur_elem->high, cur_elem->down);
+        if(cur_elem->down)
+            H5S__hyper_print_spans_dfs(f, cur_elem->down, depth + 1, dims);
+        cur_elem = cur_elem->next;
+    } /* end while */
+
+    FUNC_LEAVE_NOAPI(SUCCEED)
+} /* end H5S__hyper_print_spans_dfs() */
+
+
+/*--------------------------------------------------------------------------
+ NAME
+    H5S__hyper_print_space_dfs
+ PURPOSE
+    Output the span elements for one hyperslab selection space in depth-first order
+ USAGE
+    herr_t H5S__hyper_print_space_dfs(f, space)
+        FILE *f;               IN: the file to output
+        const H5S_t *space;    IN: the selection space to output
+ RETURNS
+    non-negative on success, negative on failure
+ GLOBAL VARIABLES
+ COMMENTS, BUGS, ASSUMPTIONS
+ EXAMPLES
+ REVISION LOG
+--------------------------------------------------------------------------*/
+static herr_t
+H5S__hyper_print_space_dfs(FILE *f, const H5S_t *space)
+{
+    const H5S_hyper_sel_t *hslab = space->select.sel_info.hslab;
+    const unsigned dims = space->extent.rank;
+    unsigned u;
+
+    FUNC_ENTER_STATIC_NOERR
+
+    HDassert(hslab);
+
+    HDfprintf(f, "=======================\n");
+    HDfprintf(f, "SPACE: span_lst=%p, #dims=%u, offset_changed=%d\n", hslab->span_lst, dims, space->select.offset_changed);
+
+    HDfprintf(f, "       offset=[");
+    for(u = 0; u < dims - 1; u++)
+        HDfprintf(f, "%lld,", space->select.offset[u]);
+    HDfprintf(f, "%lld]\n", space->select.offset[dims - 1]);
+
+    HDfprintf(f, "       low_bounds=[");
+    if(space->select.sel_info.hslab->diminfo_valid == H5S_DIMINFO_VALID_YES) {
+        for(u = 0; u < dims - 1; u++)
+            HDfprintf(f, "%llu,", space->select.sel_info.hslab->diminfo.low_bounds[u]);
+        HDfprintf(f, "%llu]\n", space->select.sel_info.hslab->diminfo.low_bounds[dims - 1]);
+    } /* end if */
+    else {
+        for(u = 0; u < dims - 1; u++)
+            HDfprintf(f, "%llu,", space->select.sel_info.hslab->span_lst->low_bounds[u]);
+        HDfprintf(f, "%llu]\n", space->select.sel_info.hslab->span_lst->low_bounds[dims - 1]);
+    } /* end else */
+
+    HDfprintf(f, "       high_bounds=[");
+    if(space->select.sel_info.hslab->diminfo_valid == H5S_DIMINFO_VALID_YES) {
+        for(u = 0; u < dims - 1; u++)
+            HDfprintf(f, "%llu,", space->select.sel_info.hslab->diminfo.high_bounds[u]);
+        HDfprintf(f, "%llu]\n", space->select.sel_info.hslab->diminfo.high_bounds[dims - 1]);
+    } /* end if */
+    else {
+        for(u = 0; u < dims - 1; u++)
+            HDfprintf(f, "%llu,", space->select.sel_info.hslab->span_lst->high_bounds[u]);
+        HDfprintf(f, "%llu]\n", space->select.sel_info.hslab->span_lst->high_bounds[dims - 1]);
+    } /* end else */
+
+    /* Print out diminfo, if it's valid */
+    if(space->select.sel_info.hslab->diminfo_valid == H5S_DIMINFO_VALID_YES)
+        H5S__hyper_print_diminfo(f, space);
+
+    /* Start print out the highest-order of dimension */
+    if(hslab->span_lst)
+        H5S__hyper_print_spans_dfs(f, hslab->span_lst, 0, dims);
+    HDfprintf(f, "=======================\n\n");
+
+    FUNC_LEAVE_NOAPI(SUCCEED)
+} /* end H5S__hyper_print_space_dfs() */
 #endif /* H5S_HYPER_DEBUG */
 
 
 /*-------------------------------------------------------------------------
+ * Function:    H5S__hyper_get_op_gen
+ *
+ * Purpose:    Acquire a unique operation generation value
+ *
+ * Return:    Operation generation value (can't fail)
+ *
+ * Programmer:    Quincey Koziol
+ *              Saturday, January 19, 2019
+ *
+ * Notes:       Assumes that a 64-bit value will not wrap around during
+ *              the lifespan of the process.
+ *
+ *-------------------------------------------------------------------------
+ */
+uint64_t
+H5S__hyper_get_op_gen(void)
+{
+    FUNC_ENTER_PACKAGE_NOERR
+
+    FUNC_LEAVE_NOAPI(H5S_hyper_op_gen_g++);
+} /* end H5S__hyper_op_gen() */
+
+
+/*-------------------------------------------------------------------------
  * Function:    H5S__hyper_iter_init
  *
  * Purpose:     Initializes iteration information for hyperslab selection.
@@ -304,38 +574,45 @@ H5S__hyper_print_diminfo(FILE *f, const H5S_t *space)
 static herr_t
 H5S__hyper_iter_init(const H5S_t *space, H5S_sel_iter_t *iter)
 {
-    const H5S_hyper_dim_t *tdiminfo;    /* Temporary pointer to diminfo information */
-    H5S_hyper_span_info_t *spans;   /* Pointer to hyperslab span info node */
+    hsize_t *slab_size;         /* Pointer to the dataspace dimensions to use for calc. slab */
+    hsize_t acc;                /* Accumulator for computing cumulative sizes */
+    unsigned slab_dim;          /* Rank of the fastest changing dimension for calc. slab */
     unsigned rank;              /* Dataspace's dimension rank */
     unsigned u;                 /* Index variable */
     int i;                      /* Index variable */
+    herr_t ret_value = SUCCEED; /* return value */
 
-    FUNC_ENTER_STATIC_NOERR
+    FUNC_ENTER_STATIC
 
     /* Check args */
     HDassert(space && H5S_SEL_HYPERSLABS == H5S_GET_SELECT_TYPE(space));
     HDassert(iter);
     HDassert(space->select.sel_info.hslab->unlim_dim < 0);
 
-    /* Initialize the number of points to iterate over */
-    iter->elmt_left = space->select.num_elem;
+    /* Initialize the hyperslab iterator's rank */
     iter->u.hyp.iter_rank = 0;
 
     /* Get the rank of the dataspace */
-    rank = space->extent.rank;
+    rank = iter->rank;
 
-    /* Set the temporary pointer to the dimension information */
-    tdiminfo = space->select.sel_info.hslab->diminfo.opt;
+    /* Attempt to rebuild diminfo if it is invalid and has not been confirmed
+     * to be impossible.
+     */
+    if(space->select.sel_info.hslab->diminfo_valid == H5S_DIMINFO_VALID_NO)
+        H5S__hyper_rebuild((H5S_t *)space);     /* Casting away const OK -NAF */
 
     /* Check for the special case of just one H5Sselect_hyperslab call made */
     if(space->select.sel_info.hslab->diminfo_valid == H5S_DIMINFO_VALID_YES) {
-        /* Initialize the information needed for regular hyperslab I/O */
+/* Initialize the information needed for regular hyperslab I/O */
+        const H5S_hyper_dim_t *tdiminfo;    /* Temporary pointer to diminfo information */
         const hsize_t *mem_size;    /* Temporary pointer to dataspace extent's dimension sizes */
-        hsize_t acc;                /* Accumulator for "flattened" dimension's sizes */
         unsigned cont_dim = 0;      /* # of contiguous dimensions */
 
+        /* Set the temporary pointer to the dimension information */
+        tdiminfo = space->select.sel_info.hslab->diminfo.opt;
+
         /* Set the temporary pointer to the dataspace extent's dimension sizes */
-        mem_size = space->extent.size;
+        mem_size = iter->dims;
 
         /*
          * For a regular hyperslab to be contiguous up to some dimension, it
@@ -393,7 +670,7 @@ H5S__hyper_iter_init(const H5S_t *space, H5S_sel_iter_t *iter)
                         iter->u.hyp.diminfo[curr_dim].count = tdiminfo[i].count;
                         iter->u.hyp.diminfo[curr_dim].block = tdiminfo[i].block * acc;
                         iter->u.hyp.size[curr_dim] = mem_size[i] * acc;
-                        iter->u.hyp.sel_off[curr_dim] = space->select.offset[i] * (hssize_t)acc;
+                        iter->u.hyp.sel_off[curr_dim] = iter->sel_off[i] * (hssize_t)acc;
 
                         /* Reset the "last dim flattened" flag to avoid flattened any further dimensions */
                         last_dim_flattened = FALSE;
@@ -408,7 +685,7 @@ H5S__hyper_iter_init(const H5S_t *space, H5S_sel_iter_t *iter)
                         iter->u.hyp.diminfo[curr_dim].count = tdiminfo[i].count;
                         iter->u.hyp.diminfo[curr_dim].block = tdiminfo[i].block;
                         iter->u.hyp.size[curr_dim] = mem_size[i];
-                        iter->u.hyp.sel_off[curr_dim] = space->select.offset[i];
+                        iter->u.hyp.sel_off[curr_dim] = iter->sel_off[i];
                     } /* end else */
 
                     /* Decrement "current" flattened dimension */
@@ -419,20 +696,23 @@ H5S__hyper_iter_init(const H5S_t *space, H5S_sel_iter_t *iter)
             /* Initialize "flattened" iterator offset to initial location and dataspace extent and selection information to correct values */
             for(u = 0; u < flat_rank; u++)
                 iter->u.hyp.off[u] = iter->u.hyp.diminfo[u].start;
+
+            /* Set up information for computing slab sizes */
+            slab_dim = iter->u.hyp.iter_rank - 1;
+            slab_size = iter->u.hyp.size;
         } /* end if */
         else {
+            /* Make local copy of the regular selection information */
+            HDcompile_assert(sizeof(iter->u.hyp.diminfo) == sizeof(space->select.sel_info.hslab->diminfo.opt));
+            H5MM_memcpy(iter->u.hyp.diminfo, tdiminfo, sizeof(iter->u.hyp.diminfo));
+
             /* Initialize position to initial location */
-            /* Also make local copy of the regular selection information */
-            for(u = 0; u < rank; u++) {
-                /* Regular selection information */
-                iter->u.hyp.diminfo[u].start = tdiminfo[u].start;
-                iter->u.hyp.diminfo[u].stride = tdiminfo[u].stride;
-                iter->u.hyp.diminfo[u].count = tdiminfo[u].count;
-                iter->u.hyp.diminfo[u].block = tdiminfo[u].block;
-
-                /* Position information */
+            for(u = 0; u < rank; u++)
                 iter->u.hyp.off[u] = tdiminfo[u].start;
-            } /* end if */
+
+            /* Set up information for computing slab sizes */
+            slab_dim = iter->rank - 1;
+            slab_size = iter->dims;
         } /* end else */
 
         /* Flag the diminfo information as valid in the iterator */
@@ -441,14 +721,30 @@ H5S__hyper_iter_init(const H5S_t *space, H5S_sel_iter_t *iter)
         /* Initialize irregular region information also (for release) */
         iter->u.hyp.spans = NULL;
     } /* end if */
-    else {
-/* Initialize the information needed for non-regular hyperslab I/O */
-        HDassert(space->select.sel_info.hslab->span_lst);
-        /* Make a copy of the span tree to iterate over */
-        iter->u.hyp.spans = H5S__hyper_copy_span(space->select.sel_info.hslab->span_lst);
+    else {      /* Initialize the information needed for non-regular hyperslab I/O */
+        H5S_hyper_span_info_t *spans;   /* Pointer to hyperslab span info node */
 
-        /* Set the nelem & pstride values according to the element size */
-        H5S__hyper_span_precompute(iter->u.hyp.spans, iter->elmt_size);
+        /* If this iterator is created from an API call, by default we clone the
+         *  selection now, as the dataspace could be modified or go out of scope.
+         *
+         *  However, if the H5S_SEL_ITER_SHARE_WITH_DATASPACE flag is given,
+         *  the selection is shared between the selection iterator and the
+         *  dataspace.  In this case, the application _must_not_ modify or
+         *  close the dataspace that the iterator is operating on, or undefined
+         *  behavior will occur.
+         */
+        if((iter->flags & H5S_SEL_ITER_API_CALL) &&
+                !(iter->flags & H5S_SEL_ITER_SHARE_WITH_DATASPACE)) {
+            /* Copy the span tree */
+            if(NULL == (iter->u.hyp.spans = H5S__hyper_copy_span(space->select.sel_info.hslab->span_lst, space->extent.rank)))
+                HGOTO_ERROR(H5E_DATASPACE, H5E_CANTCOPY, FAIL, "can't copy span tree")
+        } /* end if */
+        else {
+            /* Share the source dataspace's span tree by incrementing the reference count on it */
+            HDassert(space->select.sel_info.hslab->span_lst);
+            iter->u.hyp.spans = space->select.sel_info.hslab->span_lst;
+            iter->u.hyp.spans->count++;
+        } /* end else */
 
         /* Initialize the starting span_info's and spans */
         spans = iter->u.hyp.spans;
@@ -467,14 +763,33 @@ H5S__hyper_iter_init(const H5S_t *space, H5S_sel_iter_t *iter)
             spans = spans->head->down;
         } /* end for */
 
+        /* Set up information for computing slab sizes */
+        slab_dim = iter->rank - 1;
+        slab_size = iter->dims;
+
         /* Flag the diminfo information as not valid in the iterator */
         iter->u.hyp.diminfo_valid = FALSE;
     } /* end else */
 
+    /* Compute the cumulative size of dataspace dimensions */
+    for(i = (int)slab_dim, acc = iter->elmt_size; i >= 0; i--) {
+        iter->u.hyp.slab[i] = acc;
+        acc *= slab_size[i];
+    } /* end for */
+
+    /* Initialize more information for irregular hyperslab selections */
+    if(!iter->u.hyp.diminfo_valid) {
+        /* Set the offset of the first element iterated on, in each dimension */
+        for(u = 0; u < rank; u++)
+            /* Compute the sequential element offset */
+            iter->u.hyp.loc_off[u] = ((hsize_t)((hssize_t)iter->u.hyp.off[u] + iter->sel_off[u])) * iter->u.hyp.slab[u];
+    } /* end if */
+
     /* Initialize type of selection iterator */
     iter->type = H5S_sel_iter_hyper;
 
-    FUNC_LEAVE_NOAPI(SUCCEED)
+done:
+    FUNC_LEAVE_NOAPI(ret_value)
 } /* end H5S__hyper_iter_init() */
 
 
@@ -1077,226 +1392,1461 @@ H5S__hyper_iter_next_block(H5S_sel_iter_t *iter)
 
 /*--------------------------------------------------------------------------
  NAME
-    H5S__hyper_iter_release
+    H5S__hyper_iter_get_seq_list_gen
  PURPOSE
-    Release hyperslab selection iterator information for a dataspace
+    Create a list of offsets & lengths for a selection
  USAGE
-    herr_t H5S__hyper_iter_release(iter)
-        H5S_sel_iter_t *iter;       IN: Pointer to selection iterator
+    herr_t H5S__hyper_iter_get_seq_list_gen(iter,maxseq,maxelem,nseq,nelem,off,len)
+        H5S_sel_iter_t *iter;   IN/OUT: Selection iterator describing last
+                                    position of interest in selection.
+        size_t maxseq;          IN: Maximum number of sequences to generate
+        size_t maxelem;         IN: Maximum number of elements to include in the
+                                    generated sequences
+        size_t *nseq;           OUT: Actual number of sequences generated
+        size_t *nelem;          OUT: Actual number of elements in sequences generated
+        hsize_t *off;           OUT: Array of offsets
+        size_t *len;            OUT: Array of lengths
  RETURNS
     Non-negative on success/Negative on failure
  DESCRIPTION
-    Releases all information for a dataspace hyperslab selection iterator
+    Use the selection in the dataspace to generate a list of byte offsets and
+    lengths for the region(s) selected.  Start/Restart from the position in the
+    ITER parameter.  The number of sequences generated is limited by the MAXSEQ
+    parameter and the number of sequences actually generated is stored in the
+    NSEQ parameter.
  GLOBAL VARIABLES
  COMMENTS, BUGS, ASSUMPTIONS
  EXAMPLES
  REVISION LOG
 --------------------------------------------------------------------------*/
 static herr_t
-H5S__hyper_iter_release(H5S_sel_iter_t *iter)
+H5S__hyper_iter_get_seq_list_gen(H5S_sel_iter_t *iter, size_t maxseq, size_t maxelem,
+    size_t *nseq, size_t *nelem, hsize_t *off, size_t *len)
 {
+    H5S_hyper_span_t *curr_span;    /* Current hyperslab span node */
+    H5S_hyper_span_t **ispan;       /* Iterator's hyperslab span nodes */
+    hsize_t *slab;      /* Cumulative size of each dimension in bytes */
+    hsize_t loc_off;    /* Byte offset in the dataspace */
+    hsize_t last_span_end = 0; /* The offset of the end of the last span */
+    hsize_t *abs_arr;   /* Absolute hyperslab span position, in elements */
+    hsize_t *loc_arr;   /* Byte offset of hyperslab span position within buffer */
+    const hssize_t *sel_off;  /* Offset within the dataspace extent */
+    size_t span_elmts = 0; /* Number of elements to actually use for this span */
+    size_t span_size = 0; /* Number of bytes in current span to actually process */
+    size_t io_left;     /* Initial number of elements to process */
+    size_t io_elmts_left;   /* Number of elements left to process */
+    size_t io_used;     /* Number of elements processed */
+    size_t curr_seq = 0; /* Number of sequence/offsets stored in the arrays */
+    size_t elem_size;   /* Size of each element iterating over */
+    unsigned ndims;     /* Number of dimensions of dataset */
+    unsigned fast_dim;  /* Rank of the fastest changing dimension for the dataspace */
+    int curr_dim;       /* Current dimension being operated on */
+    unsigned u;         /* Index variable */
+
     FUNC_ENTER_STATIC_NOERR
 
     /* Check args */
     HDassert(iter);
+    HDassert(maxseq > 0);
+    HDassert(maxelem > 0);
+    HDassert(nseq);
+    HDassert(nelem);
+    HDassert(off);
+    HDassert(len);
 
-/* Release the information needed for non-regular hyperslab I/O */
-    /* Free the copy of the selections span tree */
-    if(iter->u.hyp.spans != NULL)
-        H5S__hyper_free_span_info(iter->u.hyp.spans);
+    /* Set the rank of the fastest changing dimension */
+    ndims = iter->rank;
+    fast_dim = (ndims - 1);
+
+    /* Get the pointers to the current span info and span nodes */
+    curr_span = iter->u.hyp.span[fast_dim];
+    abs_arr = iter->u.hyp.off;
+    loc_arr = iter->u.hyp.loc_off;
+    slab = iter->u.hyp.slab;
+    sel_off = iter->sel_off;
+    ispan = iter->u.hyp.span;
+    elem_size = iter->elmt_size;
+
+    /* Set the amount of elements to perform I/O on, etc. */
+    H5_CHECK_OVERFLOW(iter->elmt_left, hsize_t, size_t);
+    io_elmts_left = io_left = MIN(maxelem, (size_t)iter->elmt_left);
+
+    /* Set the offset of the first element iterated on */
+    for(u = 0, loc_off = 0; u < ndims; u++)
+        loc_off += loc_arr[u];
+
+    /* Take care of any partial spans leftover from previous I/Os */
+    if(abs_arr[fast_dim] != curr_span->low) {
+        /* Finish the span in the fastest changing dimension */
+
+        /* Compute the number of elements to attempt in this span */
+        H5_CHECKED_ASSIGN(span_elmts, size_t, ((curr_span->high - abs_arr[fast_dim]) + 1), hsize_t);
+
+        /* Check number of elements against upper bounds allowed */
+        if(span_elmts > io_elmts_left)
+            span_elmts = io_elmts_left;
+
+        /* Set the span_size, in bytes */
+        span_size = span_elmts * elem_size;
+
+        /* Add the partial span to the list of sequences */
+        off[curr_seq] = loc_off;
+        len[curr_seq] = span_size;
+
+        /* Increment sequence count */
+        curr_seq++;
+
+        /* Set the location of the last span's end */
+        last_span_end = loc_off + span_size;
+
+        /* Decrement I/O left to perform */
+        io_elmts_left -= span_elmts;
+
+        /* Check if we are done */
+        if(io_elmts_left > 0) {
+            /* Move to next span in fastest changing dimension */
+            curr_span = curr_span->next;
+
+            if(NULL != curr_span) {
+                /* Move location offset of destination */
+                loc_off += (curr_span->low - abs_arr[fast_dim]) * elem_size;
+
+                /* Move iterator for fastest changing dimension */
+                abs_arr[fast_dim] = curr_span->low;
+                loc_arr[fast_dim] = ((hsize_t)((hssize_t)curr_span->low + sel_off[fast_dim])) * slab[fast_dim];
+                ispan[fast_dim] = curr_span;
+            } /* end if */
+        } /* end if */
+        else {
+            /* Advance the hyperslab iterator */
+            abs_arr[fast_dim] += span_elmts;
+
+            /* Check if we are still within the span */
+            if(abs_arr[fast_dim] <= curr_span->high) {
+                /* Sanity check */
+                HDassert(ispan[fast_dim] == curr_span);
+
+                /* Update byte offset */
+                loc_arr[fast_dim] += span_size;
+            } /* end if */
+            /* If we walked off that span, advance to the next span */
+            else {
+                /* Advance span in this dimension */
+                curr_span = curr_span->next;
+
+                /* Check if we have a valid span in this dimension still */
+                if(NULL != curr_span) {
+                    /* Reset absolute position */
+                    abs_arr[fast_dim] = curr_span->low;
+
+                    /* Update location offset */
+                    loc_arr[fast_dim] = ((hsize_t)((hssize_t)curr_span->low + sel_off[fast_dim])) * slab[fast_dim];
+
+                    /* Reset the span in the current dimension */
+                    ispan[fast_dim] = curr_span;
+                } /* end if */
+            } /* end else */
+        } /* end else */
+
+        /* Adjust iterator pointers */
+
+        if(NULL == curr_span) {
+/* Same as code in main loop */
+            /* Start at the next fastest dim */
+            curr_dim = (int)(fast_dim - 1);
+
+            /* Work back up through the dimensions */
+            while(curr_dim >= 0) {
+                /* Reset the current span */
+                curr_span = ispan[curr_dim];
+
+                /* Increment absolute position */
+                abs_arr[curr_dim]++;
+
+                /* Check if we are still within the span */
+                if(abs_arr[curr_dim] <= curr_span->high) {
+                    /* Update location offset */
+                    loc_arr[curr_dim] += slab[curr_dim];
+
+                    break;
+                } /* end if */
+                /* If we walked off that span, advance to the next span */
+                else {
+                    /* Advance span in this dimension */
+                    curr_span = curr_span->next;
+
+                    /* Check if we have a valid span in this dimension still */
+                    if(NULL != curr_span) {
+                        /* Reset the span in the current dimension */
+                        ispan[curr_dim] = curr_span;
+
+                        /* Reset absolute position */
+                        abs_arr[curr_dim] = curr_span->low;
+
+                        /* Update byte location */
+                        loc_arr[curr_dim] = ((hsize_t)((hssize_t)curr_span->low + sel_off[curr_dim])) * slab[curr_dim];
+
+                        break;
+                    } /* end if */
+                    else
+                        /* If we finished the span list in this dimension, decrement the dimension worked on and loop again */
+                        curr_dim--;
+                } /* end else */
+            } /* end while */
+
+            /* Check if we have more spans in the tree */
+            if(curr_dim >= 0) {
+                /* Walk back down the iterator positions, resetting them */
+                while((unsigned)curr_dim < fast_dim) {
+                    HDassert(curr_span);
+                    HDassert(curr_span->down);
+                    HDassert(curr_span->down->head);
+
+                    /* Increment current dimension */
+                    curr_dim++;
+
+                    /* Set the new span_info & span for this dimension */
+                    ispan[curr_dim] = curr_span->down->head;
+
+                    /* Advance span down the tree */
+                    curr_span = curr_span->down->head;
+
+                    /* Reset the absolute offset for the dim */
+                    abs_arr[curr_dim] = curr_span->low;
+
+                    /* Update the location offset */
+                    loc_arr[curr_dim] = ((hsize_t)((hssize_t)curr_span->low + sel_off[curr_dim])) * slab[curr_dim];
+                } /* end while */
+
+                /* Verify that the curr_span points to the fastest dim */
+                HDassert(curr_span == ispan[fast_dim]);
+
+                /* Reset the buffer offset */
+                for(u = 0, loc_off = 0; u < ndims; u++)
+                    loc_off += loc_arr[u];
+            } /* end else */
+            else
+                /* We had better be done with I/O or bad things are going to happen... */
+                HDassert(io_elmts_left == 0);
+        } /* end if */
+    } /* end if */
+
+    /* Perform the I/O on the elements, based on the position of the iterator */
+    while(io_elmts_left > 0 && curr_seq < maxseq) {
+        H5S_hyper_span_t *prev_span;    /* Previous hyperslab span node */
+
+        /* Sanity check */
+        HDassert(curr_span);
+
+        /* Set to current span, so the first adjustment to loc_off is 0 */
+        prev_span = curr_span;
+
+        /* Loop over all the spans in the fastest changing dimension */
+        while(curr_span != NULL) {
+            hsize_t nelmts;     /* # of elements covered by current span */
+
+            /* Move location offset of current span */
+            loc_off += (curr_span->low - prev_span->low) * elem_size;
+
+            /* Compute the number of elements to attempt in this span */
+            nelmts = (curr_span->high - curr_span->low) + 1;
+            H5_CHECKED_ASSIGN(span_elmts, size_t, nelmts, hsize_t);
+
+            /* Check number of elements against upper bounds allowed */
+            if(span_elmts >= io_elmts_left) {
+                /* Trim the number of elements to output */
+                span_elmts = io_elmts_left;
+                span_size = span_elmts * elem_size;
+                io_elmts_left = 0;
+
+/* COMMON */
+                /* Store the I/O information for the span */
+
+                /* Check if this is appending onto previous sequence */
+                if(curr_seq > 0 && last_span_end == loc_off)
+                    len[curr_seq - 1] += span_size;
+                else {
+                    off[curr_seq] = loc_off;
+                    len[curr_seq] = span_size;
+
+                    /* Increment the number of sequences in arrays */
+                    curr_seq++;
+                } /* end else */
+/* end COMMON */
+
+                /* Break out now, we are finished with I/O */
+                break;
+            } /* end if */
+            else {
+                /* Decrement I/O left to perform */
+                span_size = span_elmts * elem_size;
+                io_elmts_left -= span_elmts;
+
+/* COMMON */
+                /* Store the I/O information for the span */
+
+                /* Check if this is appending onto previous sequence */
+                if(curr_seq > 0 && last_span_end == loc_off)
+                    len[curr_seq - 1] += span_size;
+                else {
+                    off[curr_seq] = loc_off;
+                    len[curr_seq] = span_size;
+
+                    /* Increment the number of sequences in arrays */
+                    curr_seq++;
+                } /* end else */
+/* end COMMON */
+
+                /* If the sequence & offset arrays are full, do what? */
+                if(curr_seq >= maxseq)
+                    /* Break out now, we are finished with sequences */
+                    break;
+            } /* end else */
+
+            /* Set the location of the last span's end */
+            last_span_end = loc_off + span_size;
+
+        /* Move to next span in fastest changing dimension */
+            prev_span = curr_span;
+        curr_span = curr_span->next;
+        } /* end while */
+
+        /* Check if we are done */
+        if(io_elmts_left == 0 || curr_seq >= maxseq) {
+            /* Sanity checks */
+            HDassert(curr_span);
+
+            /* Update absolute position */
+            abs_arr[fast_dim] = curr_span->low + span_elmts;
+
+            /* Check if we are still within the span */
+            if(abs_arr[fast_dim] <= curr_span->high) {
+                /* Reset the span for the fast dimension */
+                ispan[fast_dim] = curr_span;
+
+                /* Update location offset */
+                loc_arr[fast_dim] = ((hsize_t)((hssize_t)curr_span->low + (hssize_t)span_elmts + sel_off[fast_dim])) * slab[fast_dim];
+
+                break;
+            } /* end if */
+            /* If we walked off that span, advance to the next span */
+            else {
+                /* Advance span in this dimension */
+                curr_span = curr_span->next;
+
+                /* Check if we have a valid span in this dimension still */
+                if(curr_span != NULL) {
+                    /* Reset absolute position */
+                    abs_arr[fast_dim] = curr_span->low;
+                    loc_arr[fast_dim] = ((hsize_t)((hssize_t)curr_span->low + sel_off[fast_dim])) * slab[fast_dim];
+                    ispan[fast_dim] = curr_span;
+
+                    break;
+                } /* end if */
+            } /* end else */
+        } /* end if */
+
+        /* Adjust iterator pointers */
+
+        /* Start at the next fastest dim */
+        curr_dim = (int)(fast_dim - 1);
+
+        /* Work back up through the dimensions */
+        while(curr_dim >= 0) {
+            /* Reset the current span */
+            curr_span = ispan[curr_dim];
+
+            /* Increment absolute position */
+            abs_arr[curr_dim]++;
+
+            /* Check if we are still within the span */
+            if(abs_arr[curr_dim] <= curr_span->high) {
+                /* Update location offset */
+                loc_arr[curr_dim] += slab[curr_dim];
+
+                break;
+            } /* end if */
+            /* If we walked off that span, advance to the next span */
+            else {
+                /* Advance span in this dimension */
+                curr_span = curr_span->next;
+
+                /* Check if we have a valid span in this dimension still */
+                if(curr_span != NULL) {
+                    /* Reset the span in the current dimension */
+                    ispan[curr_dim] = curr_span;
+
+                    /* Reset absolute position */
+                    abs_arr[curr_dim] = curr_span->low;
+
+                    /* Update location offset */
+                    loc_arr[curr_dim] = ((hsize_t)((hssize_t)curr_span->low + sel_off[curr_dim])) * slab[curr_dim];
+
+                    break;
+                } /* end if */
+                else
+                    /* If we finished the span list in this dimension, decrement the dimension worked on and loop again */
+                    curr_dim--;
+            } /* end else */
+        } /* end while */
+
+        /* Check if we are finished with the spans in the tree */
+        if(curr_dim < 0) {
+            /* We had better be done with I/O or bad things are going to happen... */
+            HDassert(io_elmts_left == 0);
+            break;
+        } /* end if */
+        else {
+            /* Walk back down the iterator positions, resetting them */
+            while((unsigned)curr_dim < fast_dim) {
+                HDassert(curr_span);
+                HDassert(curr_span->down);
+                HDassert(curr_span->down->head);
+
+                /* Increment current dimension to the next dimension down */
+                curr_dim++;
+
+                /* Set the new span for the next dimension down */
+                ispan[curr_dim] = curr_span->down->head;
+
+                /* Advance span down the tree */
+                curr_span = curr_span->down->head;
+
+                /* Reset the absolute offset for the dim */
+                abs_arr[curr_dim] = curr_span->low;
+
+                /* Update location offset */
+                loc_arr[curr_dim] = ((hsize_t)((hssize_t)curr_span->low + sel_off[curr_dim])) * slab[curr_dim];
+            } /* end while */
+
+            /* Verify that the curr_span points to the fastest dim */
+            HDassert(curr_span == ispan[fast_dim]);
+        } /* end else */
+
+        /* Reset the buffer offset */
+        for(u = 0, loc_off = 0; u < ndims; u++)
+            loc_off += loc_arr[u];
+    } /* end while */
+
+    /* Decrement number of elements left in iterator */
+    io_used = io_left - io_elmts_left;
+    iter->elmt_left -= io_used;
+
+    /* Set the number of sequences generated */
+    *nseq = curr_seq;
+
+    /* Set the number of elements used */
+    *nelem = io_used;
 
     FUNC_LEAVE_NOAPI(SUCCEED)
-} /* end H5S__hyper_iter_release() */
+} /* end H5S__hyper_iter_get_seq_list_gen() */
 
 
 /*--------------------------------------------------------------------------
  NAME
-    H5S__hyper_new_span
+    H5S__hyper_iter_get_seq_list_opt
  PURPOSE
-    Make a new hyperslab span node
+    Create a list of offsets & lengths for a selection
  USAGE
-    H5S_hyper_span_t *H5S__hyper_new_span(low, high, down, next)
-        hsize_t low, high;         IN: Low and high bounds for new span node
-        H5S_hyper_span_info_t *down;     IN: Down span tree for new node
-        H5S_hyper_span_t *next;     IN: Next span for new node
+    herr_t H5S__hyper_iter_get_seq_list_opt(iter,maxseq,maxelem,nseq,nelem,off,len)
+        H5S_sel_iter_t *iter;   IN/OUT: Selection iterator describing last
+                                    position of interest in selection.
+        size_t maxseq;          IN: Maximum number of sequences to generate
+        size_t maxelem;         IN: Maximum number of elements to include in the
+                                    generated sequences
+        size_t *nseq;           OUT: Actual number of sequences generated
+        size_t *nelem;          OUT: Actual number of elements in sequences generated
+        hsize_t *off;           OUT: Array of offsets
+        size_t *len;            OUT: Array of lengths
  RETURNS
-    Pointer to next span node on success, NULL on failure
+    Non-negative on success/Negative on failure.
  DESCRIPTION
-    Allocate and initialize a new hyperslab span node, filling in the low &
-    high bounds, the down span and next span pointers also.  Increment the
-    reference count of the 'down span' if applicable.
+    Use the selection in the dataspace to generate a list of byte offsets and
+    lengths for the region(s) selected.  Start/Restart from the position in the
+    ITER parameter.  The number of sequences generated is limited by the MAXSEQ
+    parameter and the number of sequences actually generated is stored in the
+    NSEQ parameter.
  GLOBAL VARIABLES
  COMMENTS, BUGS, ASSUMPTIONS
  EXAMPLES
  REVISION LOG
 --------------------------------------------------------------------------*/
-static H5S_hyper_span_t *
-H5S__hyper_new_span(hsize_t low, hsize_t high, H5S_hyper_span_info_t *down, H5S_hyper_span_t *next)
+static herr_t
+H5S__hyper_iter_get_seq_list_opt(H5S_sel_iter_t *iter, size_t maxseq, size_t maxelem,
+    size_t *nseq, size_t *nelem, hsize_t *off, size_t *len)
 {
-    H5S_hyper_span_t *ret_value = NULL;         /* Return value */
+    hsize_t *mem_size;                  /* Size of the source buffer */
+    hsize_t *slab;                      /* Hyperslab size */
+    const hssize_t *sel_off;            /* Selection offset in dataspace */
+    hsize_t offset[H5S_MAX_RANK];       /* Coordinate offset in dataspace */
+    hsize_t tmp_count[H5S_MAX_RANK];    /* Temporary block count */
+    hsize_t tmp_block[H5S_MAX_RANK];    /* Temporary block offset */
+    hsize_t wrap[H5S_MAX_RANK];         /* Bytes to wrap around at the end of a row */
+    hsize_t skip[H5S_MAX_RANK];         /* Bytes to skip between blocks */
+    const H5S_hyper_dim_t *tdiminfo;    /* Temporary pointer to diminfo information */
+    hsize_t fast_dim_start,    /* Local copies of fastest changing dimension info */
+        fast_dim_stride,
+        fast_dim_block,
+        fast_dim_offset;
+    size_t fast_dim_buf_off;    /* Local copy of amount to move fastest dimension buffer offset */
+    size_t fast_dim_count;      /* Number of blocks left in fastest changing dimension */
+    size_t tot_blk_count;       /* Total number of blocks left to output */
+    size_t act_blk_count;       /* Actual number of blocks to output */
+    size_t total_rows;          /* Total number of entire rows to output */
+    size_t curr_rows;           /* Current number of entire rows to output */
+    unsigned fast_dim;  /* Rank of the fastest changing dimension for the dataspace */
+    unsigned ndims;     /* Number of dimensions of dataset */
+    int temp_dim;       /* Temporary rank holder */
+    hsize_t loc;        /* Coordinate offset */
+    size_t curr_seq = 0; /* Current sequence being operated on */
+    size_t actual_elem; /* The actual number of elements to count */
+    size_t actual_bytes;/* The actual number of bytes to copy */
+    size_t io_left;     /* The number of elements left in I/O operation */
+    size_t start_io_left; /* The initial number of elements left in I/O operation */
+    size_t elem_size;   /* Size of each element iterating over */
+    unsigned u;         /* Local index variable */
 
-    FUNC_ENTER_STATIC
+    FUNC_ENTER_STATIC_NOERR
 
-    /* Allocate a new span node */
-    if(NULL == (ret_value = H5FL_MALLOC(H5S_hyper_span_t)))
-        HGOTO_ERROR(H5E_DATASPACE, H5E_CANTALLOC, NULL, "can't allocate hyperslab span")
+    /* Check args */
+    HDassert(iter);
+    HDassert(maxseq > 0);
+    HDassert(maxelem > 0);
+    HDassert(nseq);
+    HDassert(nelem);
+    HDassert(off);
+    HDassert(len);
 
-    /* Copy the span's basic information */
-    ret_value->low = low;
-    ret_value->high = high;
-    ret_value->nelem = (high - low) + 1;
-    ret_value->pstride = 0;
-    ret_value->down = down;
-    ret_value->next = next;
+    /* Set the local copy of the diminfo pointer */
+    tdiminfo = iter->u.hyp.diminfo;
 
-    /* Increment the reference count of the 'down span' if there is one */
-    if(ret_value->down)
-        ret_value->down->count++;
+    /* Check if this is a "flattened" regular hyperslab selection */
+    if(iter->u.hyp.iter_rank != 0 && iter->u.hyp.iter_rank < iter->rank) {
+        /* Set the aliases for a few important dimension ranks */
+        ndims = iter->u.hyp.iter_rank;
 
-done:
-    FUNC_LEAVE_NOAPI(ret_value)
-} /* end H5S__hyper_new_span() */
+        /* Set the local copy of the selection offset */
+        sel_off = iter->u.hyp.sel_off;
+
+        /* Set up the pointer to the size of the memory dataspace */
+        mem_size = iter->u.hyp.size;
+    } /* end if */
+    else {
+        /* Set the aliases for a few important dimension ranks */
+        ndims = iter->rank;
+
+        /* Set the local copy of the selection offset */
+        sel_off = iter->sel_off;
+
+        /* Set up the pointer to the size of the memory dataspace */
+        mem_size = iter->dims;
+    } /* end else */
+
+    /* Set up some local variables */
+    fast_dim = ndims - 1;
+    elem_size = iter->elmt_size;
+    slab = iter->u.hyp.slab;
+
+    /* Calculate the number of elements to sequence through */
+    H5_CHECK_OVERFLOW(iter->elmt_left, hsize_t, size_t);
+    io_left = MIN((size_t)iter->elmt_left, maxelem);
+
+    /* Sanity check that there aren't any "remainder" sequences in process */
+    HDassert(!((iter->u.hyp.off[fast_dim] - tdiminfo[fast_dim].start) % tdiminfo[fast_dim].stride != 0 ||
+            ((iter->u.hyp.off[fast_dim] != tdiminfo[fast_dim].start) && tdiminfo[fast_dim].count == 1)));
+
+    /* We've cleared the "remainder" of the previous fastest dimension
+     * sequence before calling this routine, so we must be at the beginning of
+     * a sequence.  Use the fancy algorithm to compute the offsets and run
+     * through as many as possible, until the buffer fills up.
+     */
+
+    /* Keep the number of elements we started with */
+    start_io_left = io_left;
+
+    /* Compute the arrays to perform I/O on */
+
+    /* Copy the location of the point to get */
+    /* (Add in the selection offset) */
+    for(u = 0; u < ndims; u++)
+        offset[u] = (hsize_t)((hssize_t)iter->u.hyp.off[u] + sel_off[u]);
+
+    /* Compute the current "counts" for this location */
+    for(u = 0; u < ndims; u++) {
+        if(tdiminfo[u].count == 1) {
+            tmp_count[u] = 0;
+            tmp_block[u] = iter->u.hyp.off[u] - tdiminfo[u].start;
+        } /* end if */
+        else {
+            tmp_count[u] = (iter->u.hyp.off[u] - tdiminfo[u].start) / tdiminfo[u].stride;
+            tmp_block[u] = (iter->u.hyp.off[u] - tdiminfo[u].start) % tdiminfo[u].stride;
+        } /* end else */
+    } /* end for */
+
+    /* Compute the initial buffer offset */
+    for(u = 0, loc = 0; u < ndims; u++)
+        loc += offset[u] * slab[u];
+
+    /* Set the number of elements to write each time */
+    H5_CHECKED_ASSIGN(actual_elem, size_t, tdiminfo[fast_dim].block, hsize_t);
+
+    /* Set the number of actual bytes */
+    actual_bytes = actual_elem * elem_size;
+
+    /* Set local copies of information for the fastest changing dimension */
+    fast_dim_start = tdiminfo[fast_dim].start;
+    fast_dim_stride = tdiminfo[fast_dim].stride;
+    fast_dim_block = tdiminfo[fast_dim].block;
+    H5_CHECKED_ASSIGN(fast_dim_buf_off, size_t, slab[fast_dim] * fast_dim_stride, hsize_t);
+    fast_dim_offset = (hsize_t)((hssize_t)fast_dim_start + sel_off[fast_dim]);
+
+    /* Compute the number of blocks which would fit into the buffer */
+    H5_CHECK_OVERFLOW(io_left / fast_dim_block, hsize_t, size_t);
+    tot_blk_count = (size_t)(io_left / fast_dim_block);
+
+    /* Don't go over the maximum number of sequences allowed */
+    tot_blk_count = MIN(tot_blk_count, (maxseq - curr_seq));
+
+    /* Compute the amount to wrap at the end of each row */
+    for(u = 0; u < ndims; u++)
+        wrap[u] = (mem_size[u] - (tdiminfo[u].stride * tdiminfo[u].count)) * slab[u];
+
+    /* Compute the amount to skip between blocks */
+    for(u = 0; u < ndims; u++)
+        skip[u] = (tdiminfo[u].stride - tdiminfo[u].block) * slab[u];
+
+    /* Check if there is a partial row left (with full blocks) */
+    if(tmp_count[fast_dim] > 0) {
+        /* Get number of blocks in fastest dimension */
+        H5_CHECKED_ASSIGN(fast_dim_count, size_t, tdiminfo[fast_dim].count - tmp_count[fast_dim], hsize_t);
+
+        /* Make certain this entire row will fit into buffer */
+        fast_dim_count = MIN(fast_dim_count, tot_blk_count);
+
+        /* Number of blocks to sequence over */
+        act_blk_count = fast_dim_count;
+
+        /* Loop over all the blocks in the fastest changing dimension */
+        while(fast_dim_count > 0) {
+            /* Store the sequence information */
+            off[curr_seq] = loc;
+            len[curr_seq] = actual_bytes;
+
+            /* Increment sequence count */
+            curr_seq++;
+
+            /* Increment information to reflect block just processed */
+            loc += fast_dim_buf_off;
+
+            /* Decrement number of blocks */
+            fast_dim_count--;
+        } /* end while */
+
+        /* Decrement number of elements left */
+        io_left -= actual_elem * act_blk_count;
+
+        /* Decrement number of blocks left */
+        tot_blk_count -= act_blk_count;
+
+        /* Increment information to reflect block just processed */
+        tmp_count[fast_dim] += act_blk_count;
+
+        /* Check if we finished the entire row of blocks */
+        if(tmp_count[fast_dim] >= tdiminfo[fast_dim].count) {
+            /* Increment offset in destination buffer */
+            loc += wrap[fast_dim];
+
+            /* Increment information to reflect block just processed */
+            offset[fast_dim] = fast_dim_offset;    /* reset the offset in the fastest dimension */
+            tmp_count[fast_dim] = 0;
+
+            /* Increment the offset and count for the other dimensions */
+            temp_dim = (int)fast_dim - 1;
+            while(temp_dim >= 0) {
+                /* Move to the next row in the curent dimension */
+                offset[temp_dim]++;
+                tmp_block[temp_dim]++;
+
+                /* If this block is still in the range of blocks to output for the dimension, break out of loop */
+                if(tmp_block[temp_dim] < tdiminfo[temp_dim].block)
+                    break;
+                else {
+                    /* Move to the next block in the current dimension */
+                    offset[temp_dim] += (tdiminfo[temp_dim].stride - tdiminfo[temp_dim].block);
+                    loc += skip[temp_dim];
+                    tmp_block[temp_dim] = 0;
+                    tmp_count[temp_dim]++;
+
+                    /* If this block is still in the range of blocks to output for the dimension, break out of loop */
+                    if(tmp_count[temp_dim] < tdiminfo[temp_dim].count)
+                        break;
+                    else {
+                        offset[temp_dim] = (hsize_t)((hssize_t)tdiminfo[temp_dim].start + sel_off[temp_dim]);
+                        loc += wrap[temp_dim];
+                        tmp_count[temp_dim] = 0; /* reset back to the beginning of the line */
+                        tmp_block[temp_dim] = 0;
+                    } /* end else */
+                } /* end else */
+
+                /* Decrement dimension count */
+                temp_dim--;
+            } /* end while */
+        } /* end if */
+        else {
+            /* Update the offset in the fastest dimension */
+            offset[fast_dim] += (fast_dim_stride * act_blk_count);
+        } /* end else */
+    } /* end if */
+
+    /* Compute the number of entire rows to read in */
+    H5_CHECK_OVERFLOW(tot_blk_count / tdiminfo[fast_dim].count, hsize_t, size_t);
+    curr_rows = total_rows = (size_t)(tot_blk_count / tdiminfo[fast_dim].count);
+
+    /* Reset copy of number of blocks in fastest dimension */
+    H5_CHECKED_ASSIGN(fast_dim_count, size_t, tdiminfo[fast_dim].count, hsize_t);
+
+    /* Read in data until an entire sequence can't be written out any longer */
+    while(curr_rows > 0) {
+
+#define DUFF_GUTS                                                       \
+/* Store the sequence information */                                    \
+off[curr_seq] = loc;                                                    \
+len[curr_seq] = actual_bytes;                                           \
+                                                                        \
+/* Increment sequence count */                                          \
+curr_seq++;                                                             \
+                                                                        \
+/* Increment information to reflect block just processed */             \
+loc += fast_dim_buf_off;
+
+#ifdef NO_DUFFS_DEVICE
+        /* Loop over all the blocks in the fastest changing dimension */
+        while(fast_dim_count > 0) {
+            DUFF_GUTS
+
+            /* Decrement number of blocks */
+            fast_dim_count--;
+        } /* end while */
+#else /* NO_DUFFS_DEVICE */
+        {
+            size_t duffs_index; /* Counting index for Duff's device */
+
+            duffs_index = (fast_dim_count + 7) / 8;
+            switch (fast_dim_count % 8) {
+                default:
+                    HDassert(0 && "This Should never be executed!");
+                    break;
+                case 0:
+                    do
+                      {
+                        DUFF_GUTS
+                        H5_ATTR_FALLTHROUGH
+                case 7:
+                        DUFF_GUTS
+                        H5_ATTR_FALLTHROUGH
+                case 6:
+                        DUFF_GUTS
+                        H5_ATTR_FALLTHROUGH
+                case 5:
+                        DUFF_GUTS
+                        H5_ATTR_FALLTHROUGH
+                case 4:
+                        DUFF_GUTS
+                        H5_ATTR_FALLTHROUGH
+                case 3:
+                        DUFF_GUTS
+                        H5_ATTR_FALLTHROUGH
+                case 2:
+                        DUFF_GUTS
+                        H5_ATTR_FALLTHROUGH
+                case 1:
+                        DUFF_GUTS
+                  } while (--duffs_index > 0);
+            } /* end switch */
+        }
+#endif /* NO_DUFFS_DEVICE */
+#undef DUFF_GUTS
+
+        /* Increment offset in destination buffer */
+        loc += wrap[fast_dim];
+
+        /* Increment the offset and count for the other dimensions */
+        temp_dim = (int)fast_dim - 1;
+        while(temp_dim >= 0) {
+            /* Move to the next row in the curent dimension */
+            offset[temp_dim]++;
+            tmp_block[temp_dim]++;
+
+            /* If this block is still in the range of blocks to output for the dimension, break out of loop */
+            if(tmp_block[temp_dim] < tdiminfo[temp_dim].block)
+                break;
+            else {
+                /* Move to the next block in the current dimension */
+                offset[temp_dim] += (tdiminfo[temp_dim].stride - tdiminfo[temp_dim].block);
+                loc += skip[temp_dim];
+                tmp_block[temp_dim] = 0;
+                tmp_count[temp_dim]++;
+
+                /* If this block is still in the range of blocks to output for the dimension, break out of loop */
+                if(tmp_count[temp_dim] < tdiminfo[temp_dim].count)
+                    break;
+                else {
+                    offset[temp_dim] = (hsize_t)((hssize_t)tdiminfo[temp_dim].start + sel_off[temp_dim]);
+                    loc += wrap[temp_dim];
+                    tmp_count[temp_dim] = 0; /* reset back to the beginning of the line */
+                    tmp_block[temp_dim] = 0;
+                } /* end else */
+            } /* end else */
+
+            /* Decrement dimension count */
+            temp_dim--;
+        } /* end while */
+
+        /* Decrement the number of rows left */
+        curr_rows--;
+    } /* end while */
+
+    /* Adjust the number of blocks & elements left to transfer */
+
+    /* Decrement number of elements left */
+    H5_CHECK_OVERFLOW(actual_elem * (total_rows * tdiminfo[fast_dim].count), hsize_t, size_t);
+    io_left -= (size_t)(actual_elem * (total_rows * tdiminfo[fast_dim].count));
+
+    /* Decrement number of blocks left */
+    H5_CHECK_OVERFLOW((total_rows * tdiminfo[fast_dim].count), hsize_t, size_t);
+    tot_blk_count -= (size_t)(total_rows * tdiminfo[fast_dim].count);
+
+    /* Read in partial row of blocks */
+    if(io_left > 0 && curr_seq < maxseq) {
+        /* Get remaining number of blocks left to output */
+        fast_dim_count = tot_blk_count;
+
+        /* Loop over all the blocks in the fastest changing dimension */
+        while(fast_dim_count > 0) {
+            /* Store the sequence information */
+            off[curr_seq] = loc;
+            len[curr_seq] = actual_bytes;
+
+            /* Increment sequence count */
+            curr_seq++;
+
+            /* Increment information to reflect block just processed */
+            loc += fast_dim_buf_off;
+
+            /* Decrement number of blocks */
+            fast_dim_count--;
+        } /* end while */
+
+        /* Decrement number of elements left */
+        io_left -= actual_elem * tot_blk_count;
+
+        /* Increment information to reflect block just processed */
+        offset[fast_dim] += (fast_dim_stride * tot_blk_count);    /* move the offset in the fastest dimension */
+
+        /* Handle any leftover, partial blocks in this row */
+        if(io_left > 0 && curr_seq < maxseq) {
+            actual_elem = io_left;
+            actual_bytes = actual_elem * elem_size;
+
+            /* Store the sequence information */
+            off[curr_seq] = loc;
+            len[curr_seq] = actual_bytes;
+
+            /* Increment sequence count */
+            curr_seq++;
+
+            /* Decrement the number of elements left */
+            io_left -= actual_elem;
+
+            /* Increment buffer correctly */
+            offset[fast_dim] += actual_elem;
+        } /* end if */
+
+        /* don't bother checking slower dimensions */
+        HDassert(io_left == 0 || curr_seq == maxseq);
+    } /* end if */
+
+    /* Update the iterator */
+
+    /* Update the iterator with the location we stopped */
+    /* (Subtract out the selection offset) */
+    for(u = 0; u < ndims; u++)
+        iter->u.hyp.off[u] = (hsize_t)((hssize_t)offset[u] - sel_off[u]);
+
+    /* Decrement the number of elements left in selection */
+    iter->elmt_left -= (start_io_left - io_left);
+
+    /* Increment the number of sequences generated */
+    *nseq += curr_seq;
+
+    /* Increment the number of elements used */
+    *nelem += start_io_left - io_left;
+
+    FUNC_LEAVE_NOAPI(SUCCEED)
+} /* end H5S__hyper_iter_get_seq_list_opt() */
 
 
 /*--------------------------------------------------------------------------
  NAME
-    H5S__hyper_span_precompute_helper
+    H5S__hyper_iter_get_seq_list_single
  PURPOSE
-    Helper routine to precompute the nelem and pstrides in bytes.
+    Create a list of offsets & lengths for a selection
  USAGE
-    void H5S__hyper_span_precompute_helper(span_info, elmt_size)
-        H5S_hyper_span_info_t *span_info;      IN/OUT: Span tree to work on
-        size_t elmt_size;                      IN: element size to work with
+    herr_t H5S__hyper_iter_get_seq_list_single(flags, iter, maxseq, maxelem, nseq, nelem, off, len)
+        unsigned flags;         IN: Flags for extra information about operation
+        H5S_sel_iter_t *iter;   IN/OUT: Selection iterator describing last
+                                    position of interest in selection.
+        size_t maxseq;          IN: Maximum number of sequences to generate
+        size_t maxelem;         IN: Maximum number of elements to include in the
+                                    generated sequences
+        size_t *nseq;           OUT: Actual number of sequences generated
+        size_t *nelem;          OUT: Actual number of elements in sequences generated
+        hsize_t *off;           OUT: Array of offsets
+        size_t *len;            OUT: Array of lengths
  RETURNS
-    None
+    Non-negative on success/Negative on failure.
  DESCRIPTION
-    Change the nelem and pstride values in the span tree from elements to
-    bytes using the elmt_size parameter.
+    Use the selection in the dataspace to generate a list of byte offsets and
+    lengths for the region(s) selected.  Start/Restart from the position in the
+    ITER parameter.  The number of sequences generated is limited by the MAXSEQ
+    parameter and the number of sequences actually generated is stored in the
+    NSEQ parameter.
  GLOBAL VARIABLES
  COMMENTS, BUGS, ASSUMPTIONS
  EXAMPLES
  REVISION LOG
 --------------------------------------------------------------------------*/
-static void
-H5S__hyper_span_precompute_helper(H5S_hyper_span_info_t *spans, size_t elmt_size)
+static herr_t
+H5S__hyper_iter_get_seq_list_single(H5S_sel_iter_t *iter, size_t maxseq, size_t maxelem,
+    size_t *nseq, size_t *nelem, hsize_t *off, size_t *len)
 {
+    const H5S_hyper_dim_t *tdiminfo;    /* Temporary pointer to diminfo information */
+    const hssize_t *sel_off;    /* Selection offset in dataspace */
+    hsize_t *mem_size;          /* Size of the source buffer */
+    hsize_t base_offset[H5S_MAX_RANK];  /* Base coordinate offset in dataspace */
+    hsize_t offset[H5S_MAX_RANK];       /* Coordinate offset in dataspace */
+    hsize_t *slab;              /* Hyperslab size */
+    hsize_t fast_dim_block;     /* Local copies of fastest changing dimension info */
+    hsize_t loc;                /* Coordinate offset */
+    size_t tot_blk_count;       /* Total number of blocks left to output */
+    size_t elem_size;           /* Size of each element iterating over */
+    size_t io_left;             /* The number of elements left in I/O operation */
+    size_t actual_elem;         /* The actual number of elements to count */
+    unsigned ndims;             /* Number of dimensions of dataset */
+    unsigned fast_dim;          /* Rank of the fastest changing dimension for the dataspace */
+    unsigned skip_dim;          /* Rank of the dimension to skip along */
+    unsigned u;                 /* Local index variable */
+
     FUNC_ENTER_STATIC_NOERR
 
-    /* Sanity checks */
-    HDassert(spans);
-    HDassert(spans->scratch == (H5S_hyper_span_info_t *)~((size_t)NULL) ||
-        spans->scratch == NULL);
+    /* Check args */
+    HDassert(iter);
+    HDassert(maxseq > 0);
+    HDassert(maxelem > 0);
+    HDassert(nseq);
+    HDassert(nelem);
+    HDassert(off);
+    HDassert(len);
 
-    /* Check if we've already set this down span tree */
-    if(spans->scratch != (H5S_hyper_span_info_t *)~((size_t)NULL)) {
-        H5S_hyper_span_t *span;             /* Hyperslab span */
+    /* Set a local copy of the diminfo pointer */
+    tdiminfo = iter->u.hyp.diminfo;
 
-        /* Set the tree's scratch pointer */
-        spans->scratch = (H5S_hyper_span_info_t *)~((size_t)NULL);
+    /* Check if this is a "flattened" regular hyperslab selection */
+    if(iter->u.hyp.iter_rank != 0 && iter->u.hyp.iter_rank < iter->rank) {
+        /* Set the aliases for a few important dimension ranks */
+        ndims = iter->u.hyp.iter_rank;
 
-        /* Set the scratch pointers in all the nodes */
-        span = spans->head;
+        /* Set the local copy of the selection offset */
+        sel_off = iter->u.hyp.sel_off;
 
-        /* Loop over all the spans for this down span tree */
-        while(span != NULL) {
-            /* If there are down spans, precompute their values also */
-            if(span->down != NULL)
-                H5S__hyper_span_precompute_helper(span->down, elmt_size);
+        /* Set up the pointer to the size of the memory dataspace */
+        mem_size = iter->u.hyp.size;
+    } /* end if */
+    else {
+        /* Set the aliases for a few important dimension ranks */
+        ndims = iter->rank;
 
-            /* Change the nelem & pstride values into bytes */
-            span->nelem *= elmt_size;
-            span->pstride *= elmt_size;
+        /* Set the local copy of the selection offset */
+        sel_off = iter->sel_off;
 
-            /* Advance to next span */
-            span = span->next;
-        } /* end while */
+        /* Set up the pointer to the size of the memory dataspace */
+        mem_size = iter->dims;
+    } /* end else */
+
+    /* Set up some local variables */
+    fast_dim = ndims - 1;
+    elem_size = iter->elmt_size;
+    slab = iter->u.hyp.slab;
+
+    /* Copy the base location of the block */
+    /* (Add in the selection offset) */
+    for(u = 0; u < ndims; u++)
+        base_offset[u] = (hsize_t)((hssize_t)tdiminfo[u].start + sel_off[u]);
+
+    /* Copy the location of the point to get */
+    /* (Add in the selection offset) */
+    for(u = 0; u < ndims; u++)
+        offset[u] = (hsize_t)((hssize_t)iter->u.hyp.off[u] + sel_off[u]);
+
+    /* Compute the initial buffer offset */
+    for(u = 0, loc = 0; u < ndims; u++)
+        loc += offset[u] * slab[u];
+
+    /* Set local copies of information for the fastest changing dimension */
+    fast_dim_block = tdiminfo[fast_dim].block;
+
+    /* Calculate the number of elements to sequence through */
+    H5_CHECK_OVERFLOW(iter->elmt_left, hsize_t, size_t);
+    io_left = MIN((size_t)iter->elmt_left, maxelem);
+
+    /* Compute the number of blocks which would fit into the buffer */
+    H5_CHECK_OVERFLOW(io_left / fast_dim_block, hsize_t, size_t);
+    tot_blk_count = (size_t)(io_left / fast_dim_block);
+
+    /* Don't go over the maximum number of sequences allowed */
+    tot_blk_count = MIN(tot_blk_count, maxseq);
+
+    /* Set the number of elements to write each time */
+    H5_CHECKED_ASSIGN(actual_elem, size_t, fast_dim_block, hsize_t);
+
+    /* Check for blocks to operate on */
+    if(tot_blk_count > 0) {
+        size_t actual_bytes;        /* The actual number of bytes to copy */
+
+        /* Set the number of actual bytes */
+        actual_bytes = actual_elem * elem_size;
+
+        /* Check for 1-dim selection */
+        if(0 == fast_dim) {
+            /* Sanity checks */
+            HDassert(1 == tot_blk_count);
+            HDassert(io_left == actual_elem);
+
+            /* Store the sequence information */
+            *off++ = loc;
+            *len++ = actual_bytes;
+        } /* end if */
+        else {
+            hsize_t skip_slab;          /* Temporary copy of slab[fast_dim - 1] */
+            size_t blk_count;           /* Total number of blocks left to output */
+            int i;                      /* Local index variable */
+
+            /* Find first dimension w/block >1 */
+            skip_dim = fast_dim;
+            for(i = (int)(fast_dim - 1); i >= 0; i--)
+                if(tdiminfo[i].block > 1) {
+                    skip_dim = (unsigned)i;
+                    break;
+                } /* end if */
+            skip_slab = slab[skip_dim];
+
+            /* Check for being able to use fast algorithm for 1-D */
+            if(0 == skip_dim) {
+                /* Create sequences until an entire row can't be used */
+                blk_count = tot_blk_count;
+                while(blk_count > 0) {
+                    /* Store the sequence information */
+                    *off++ = loc;
+                    *len++ = actual_bytes;
+
+                    /* Increment offset in destination buffer */
+                    loc += skip_slab;
+
+                    /* Decrement block count */
+                    blk_count--;
+                } /* end while */
+
+                /* Move to the next location */
+                offset[skip_dim] += tot_blk_count;
+            } /* end if */
+            else {
+                hsize_t tmp_block[H5S_MAX_RANK];    /* Temporary block offset */
+                hsize_t skip[H5S_MAX_RANK]; /* Bytes to skip between blocks */
+                int temp_dim;               /* Temporary rank holder */
+
+                /* Set the starting block location */
+                for(u = 0; u < ndims; u++)
+                    tmp_block[u] = iter->u.hyp.off[u] - tdiminfo[u].start;
+
+                /* Compute the amount to skip between sequences */
+                for(u = 0; u < ndims; u++)
+                    skip[u] = (mem_size[u] - tdiminfo[u].block) * slab[u];
+
+                /* Create sequences until an entire row can't be used */
+                blk_count = tot_blk_count;
+                while(blk_count > 0) {
+                    /* Store the sequence information */
+                    *off++ = loc;
+                    *len++ = actual_bytes;
+
+                    /* Set temporary dimension for advancing offsets */
+                    temp_dim = (int)skip_dim;
+
+                    /* Increment offset in destination buffer */
+                    loc += skip_slab;
+
+                    /* Increment the offset and count for the other dimensions */
+                    while(temp_dim >= 0) {
+                        /* Move to the next row in the curent dimension */
+                        offset[temp_dim]++;
+                        tmp_block[temp_dim]++;
+
+                        /* If this block is still in the range of blocks to output for the dimension, break out of loop */
+                        if(tmp_block[temp_dim] < tdiminfo[temp_dim].block)
+                            break;
+                        else {
+                            offset[temp_dim] = base_offset[temp_dim];
+                            loc += skip[temp_dim];
+                            tmp_block[temp_dim] = 0;
+                        } /* end else */
+
+                        /* Decrement dimension count */
+                        temp_dim--;
+                    } /* end while */
+
+                    /* Decrement block count */
+                    blk_count--;
+                } /* end while */
+            } /* end else */
+        } /* end else */
+
+        /* Update the iterator, if there were any blocks used */
+
+        /* Decrement the number of elements left in selection */
+        iter->elmt_left -= tot_blk_count * actual_elem;
+
+        /* Check if there are elements left in iterator */
+        if(iter->elmt_left > 0) {
+            /* Update the iterator with the location we stopped */
+            /* (Subtract out the selection offset) */
+            for(u = 0; u < ndims; u++)
+                iter->u.hyp.off[u] = (hsize_t)((hssize_t)offset[u] - sel_off[u]);
+        } /* end if */
+
+        /* Increment the number of sequences generated */
+        *nseq += tot_blk_count;
+
+        /* Increment the number of elements used */
+        *nelem += tot_blk_count * actual_elem;
     } /* end if */
 
-    FUNC_LEAVE_NOAPI_VOID
-} /* end H5S__hyper_span_precompute_helper() */
+    /* Check for partial block, with room for another sequence */
+    if(io_left > (tot_blk_count * actual_elem) && tot_blk_count < maxseq) {
+        size_t elmt_remainder;  /* Elements remaining */
+
+        /* Compute elements left */
+        elmt_remainder = io_left - (tot_blk_count * actual_elem);
+        HDassert(elmt_remainder < fast_dim_block);
+        HDassert(elmt_remainder > 0);
+
+        /* Store the sequence information */
+        *off++ = loc;
+        *len++ = elmt_remainder * elem_size;
+
+        /* Update the iterator with the location we stopped */
+        iter->u.hyp.off[fast_dim] += (hsize_t)elmt_remainder;
+
+        /* Decrement the number of elements left in selection */
+        iter->elmt_left -= elmt_remainder;
+
+        /* Increment the number of sequences generated */
+        (*nseq)++;
+
+        /* Increment the number of elements used */
+        *nelem += elmt_remainder;
+    } /* end if */
+
+    /* Sanity check */
+    HDassert(*nseq > 0);
+    HDassert(*nelem > 0);
+
+    FUNC_LEAVE_NOAPI(SUCCEED)
+} /* end H5S__hyper_iter_get_seq_list_single() */
 
 
 /*--------------------------------------------------------------------------
  NAME
-    H5S__hyper_span_precompute
+    H5S__hyper_iter_get_seq_list
  PURPOSE
-    Precompute the nelem and pstrides in bytes.
+    Create a list of offsets & lengths for a selection
  USAGE
-    herr_t H5S__hyper_span_precompute(span_info, elmt_size)
-        H5S_hyper_span_info_t *span_info;      IN/OUT: Span tree to work on
-        size_t elmt_size;                      IN: element size to work with
+    herr_t H5S__hyper_iter_get_seq_list(iter,maxseq,maxelem,nseq,nelem,off,len)
+        H5S_t *space;           IN: Dataspace containing selection to use.
+        H5S_sel_iter_t *iter;   IN/OUT: Selection iterator describing last
+                                    position of interest in selection.
+        size_t maxseq;          IN: Maximum number of sequences to generate
+        size_t maxelem;         IN: Maximum number of elements to include in the
+                                    generated sequences
+        size_t *nseq;           OUT: Actual number of sequences generated
+        size_t *nelem;          OUT: Actual number of elements in sequences generated
+        hsize_t *off;           OUT: Array of offsets (in bytes)
+        size_t *len;            OUT: Array of lengths (in bytes)
  RETURNS
-    Non-negative on success, negative on failure
+    Non-negative on success/Negative on failure.
  DESCRIPTION
-    Change the nelem and pstride values in the span tree from elements to
-    bytes using the elmt_size parameter.
+    Use the selection in the dataspace to generate a list of byte offsets and
+    lengths for the region(s) selected.  Start/Restart from the position in the
+    ITER parameter.  The number of sequences generated is limited by the MAXSEQ
+    parameter and the number of sequences actually generated is stored in the
+    NSEQ parameter.
  GLOBAL VARIABLES
  COMMENTS, BUGS, ASSUMPTIONS
  EXAMPLES
  REVISION LOG
 --------------------------------------------------------------------------*/
 static herr_t
-H5S__hyper_span_precompute(H5S_hyper_span_info_t *spans, size_t elmt_size)
+H5S__hyper_iter_get_seq_list(H5S_sel_iter_t *iter, size_t maxseq,
+    size_t maxelem, size_t *nseq, size_t *nelem, hsize_t *off, size_t *len)
 {
+    herr_t ret_value = FAIL;    /* return value */
+
     FUNC_ENTER_STATIC_NOERR
 
-    HDassert(spans);
+    /* Check args */
+    HDassert(iter);
+    HDassert(iter->elmt_left > 0);
+    HDassert(maxseq > 0);
+    HDassert(maxelem > 0);
+    HDassert(nseq);
+    HDassert(nelem);
+    HDassert(off);
+    HDassert(len);
 
-    /* Call the helper routine to actually do the work */
-    H5S__hyper_span_precompute_helper(spans, elmt_size);
+    /* Check for the special case of just one H5Sselect_hyperslab call made */
+    if(iter->u.hyp.diminfo_valid) {
+        const H5S_hyper_dim_t *tdiminfo;    /* Temporary pointer to diminfo information */
+        const hssize_t *sel_off;    /* Selection offset in dataspace */
+        unsigned ndims;         /* Number of dimensions of dataset */
+        unsigned fast_dim;      /* Rank of the fastest changing dimension for the dataspace */
+        hbool_t single_block;   /* Whether the selection is a single block */
+        unsigned u;             /* Local index variable */
 
-    /* Reset the scratch pointers for the next routine which needs them */
-    H5S__hyper_span_scratch(spans);
+        /* Set a local copy of the diminfo pointer */
+        tdiminfo = iter->u.hyp.diminfo;
 
-    FUNC_LEAVE_NOAPI(SUCCEED)
-} /* end H5S__hyper_span_precompute() */
+        /* Check if this is a "flattened" regular hyperslab selection */
+        if(iter->u.hyp.iter_rank != 0 && iter->u.hyp.iter_rank < iter->rank) {
+            /* Set the aliases for a few important dimension ranks */
+            ndims = iter->u.hyp.iter_rank;
+
+            /* Set the local copy of the selection offset */
+            sel_off = iter->u.hyp.sel_off;
+        } /* end if */
+        else {
+            /* Set the aliases for a few important dimension ranks */
+            ndims = iter->rank;
+
+            /* Set the local copy of the selection offset */
+            sel_off = iter->sel_off;
+        } /* end else */
+        fast_dim = ndims - 1;
+
+        /* Check if we stopped in the middle of a sequence of elements */
+        if((iter->u.hyp.off[fast_dim] - tdiminfo[fast_dim].start) % tdiminfo[fast_dim].stride != 0 ||
+                ((iter->u.hyp.off[fast_dim] != tdiminfo[fast_dim].start) && tdiminfo[fast_dim].count == 1)) {
+            hsize_t *slab;              /* Hyperslab size */
+            hsize_t loc;                /* Coordinate offset */
+            size_t leftover;            /* The number of elements left over from the last sequence */
+            size_t actual_elem;         /* The actual number of elements to count */
+            size_t elem_size;           /* Size of each element iterating over */
+
+            /* Calculate the number of elements left in the sequence */
+            if(tdiminfo[fast_dim].count == 1) {
+                H5_CHECKED_ASSIGN(leftover, size_t, tdiminfo[fast_dim].block - (iter->u.hyp.off[fast_dim] - tdiminfo[fast_dim].start), hsize_t);
+            } /* end if */
+            else {
+                H5_CHECKED_ASSIGN(leftover, size_t, tdiminfo[fast_dim].block - ((iter->u.hyp.off[fast_dim] - tdiminfo[fast_dim].start) % tdiminfo[fast_dim].stride), hsize_t);
+            } /* end else */
+
+            /* Make certain that we don't write too many */
+            actual_elem = MIN3(leftover, (size_t)iter->elmt_left, maxelem);
+
+            /* Set up some local variables */
+            elem_size = iter->elmt_size;
+            slab = iter->u.hyp.slab;
+
+            /* Compute the initial buffer offset */
+            for(u = 0, loc = 0; u < ndims; u++)
+                loc += ((hsize_t)((hssize_t)iter->u.hyp.off[u] + sel_off[u])) * slab[u];
+
+            /* Add a new sequence */
+            off[0] = loc;
+            H5_CHECKED_ASSIGN(len[0], size_t, actual_elem * elem_size, hsize_t);
+
+            /* Increment sequence array locations */
+            off++;
+            len++;
+
+            /* Advance the hyperslab iterator */
+            H5S__hyper_iter_next(iter, actual_elem);
+
+            /* Decrement the number of elements left in selection */
+            iter->elmt_left -= actual_elem;
+
+            /* Decrement element/sequence limits */
+            maxelem -= actual_elem;
+            maxseq--;
+
+            /* Set the number of sequences generated and elements used */
+            *nseq = 1;
+            *nelem = actual_elem;
+
+            /* Check for using up all the sequences/elements */
+            if(0 == iter->elmt_left || 0 == maxelem || 0 == maxseq)
+                return(SUCCEED);
+        } /* end if */
+        else {
+            /* Reset the number of sequences generated and elements used */
+            *nseq = 0;
+            *nelem = 0;
+        } /* end else */
+
+        /* Check for a single block selected */
+        single_block = TRUE;
+        for(u = 0; u < ndims; u++)
+            if(1 != tdiminfo[u].count) {
+                single_block = FALSE;
+                break;
+            } /* end if */
+
+        /* Check for single block selection */
+        if(single_block)
+            /* Use single-block optimized call to generate sequence list */
+            ret_value = H5S__hyper_iter_get_seq_list_single(iter, maxseq, maxelem, nseq, nelem, off, len);
+        else
+            /* Use optimized call to generate sequence list */
+            ret_value = H5S__hyper_iter_get_seq_list_opt(iter, maxseq, maxelem, nseq, nelem, off, len);
+    } /* end if */
+    else
+        /* Call the general sequence generator routine */
+        ret_value = H5S__hyper_iter_get_seq_list_gen(iter, maxseq, maxelem, nseq, nelem, off, len);
+
+    FUNC_LEAVE_NOAPI(ret_value)
+} /* end H5S__hyper_iter_get_seq_list() */
 
 
 /*--------------------------------------------------------------------------
  NAME
-    H5S__hyper_span_scratch
+    H5S__hyper_iter_release
  PURPOSE
-    Reset the scratch pointers on hyperslab span trees
+    Release hyperslab selection iterator information for a dataspace
  USAGE
-    void H5S__hyper_span_scratch(span_info)
-        H5S_hyper_span_info_t *span_info;      IN: Span tree to reset
+    herr_t H5S__hyper_iter_release(iter)
+        H5S_sel_iter_t *iter;       IN: Pointer to selection iterator
  RETURNS
-    <none>
+    Non-negative on success/Negative on failure
  DESCRIPTION
-    Reset the scratch pointers on a hyperslab span tree to NULL.
+    Releases all information for a dataspace hyperslab selection iterator
  GLOBAL VARIABLES
  COMMENTS, BUGS, ASSUMPTIONS
  EXAMPLES
  REVISION LOG
 --------------------------------------------------------------------------*/
-static void
-H5S__hyper_span_scratch(H5S_hyper_span_info_t *spans)
+static herr_t
+H5S__hyper_iter_release(H5S_sel_iter_t *iter)
 {
     FUNC_ENTER_STATIC_NOERR
 
-    HDassert(spans);
+    /* Check args */
+    HDassert(iter);
 
-    /* Check if we've already set this down span tree */
-    if(spans->scratch != NULL) {
-        H5S_hyper_span_t *span;             /* Hyperslab span */
+    /* Free the copy of the hyperslab selection span tree */
+    if(iter->u.hyp.spans != NULL)
+        H5S__hyper_free_span_info(iter->u.hyp.spans);
 
-        /* Reset the tree's scratch pointer */
-        spans->scratch = NULL;
+    FUNC_LEAVE_NOAPI(SUCCEED)
+} /* end H5S__hyper_iter_release() */
 
-        /* Set the scratch pointers in all the nodes */
-        span = spans->head;
-        while(span != NULL) {
-            /* If there are down spans, set their scratch value also */
-            if(span->down != NULL)
-                H5S__hyper_span_scratch(span->down);
+
+/*--------------------------------------------------------------------------
+ NAME
+    H5S__hyper_new_span
+ PURPOSE
+    Make a new hyperslab span node
+ USAGE
+    H5S_hyper_span_t *H5S__hyper_new_span(low, high, down, next)
+        hsize_t low, high;         IN: Low and high bounds for new span node
+        H5S_hyper_span_info_t *down;     IN: Down span tree for new node
+        H5S_hyper_span_t *next;     IN: Next span for new node
+ RETURNS
+    Pointer to new span node on success, NULL on failure
+ DESCRIPTION
+    Allocate and initialize a new hyperslab span node, filling in the low &
+    high bounds, the down span and next span pointers also.  Increment the
+    reference count of the 'down span' if applicable.
+ GLOBAL VARIABLES
+ COMMENTS, BUGS, ASSUMPTIONS
+ EXAMPLES
+ REVISION LOG
+--------------------------------------------------------------------------*/
+static H5S_hyper_span_t *
+H5S__hyper_new_span(hsize_t low, hsize_t high, H5S_hyper_span_info_t *down,
+    H5S_hyper_span_t *next)
+{
+    H5S_hyper_span_t *ret_value = NULL;         /* Return value */
 
-            /* Advance to next span */
-            span = span->next;
-        } /* end while */
-    } /* end if */
+    FUNC_ENTER_STATIC
 
-    FUNC_LEAVE_NOAPI_VOID
-} /* end H5S__hyper_span_scratch() */
+    /* Allocate a new span node */
+    if(NULL == (ret_value = H5FL_MALLOC(H5S_hyper_span_t)))
+        HGOTO_ERROR(H5E_DATASPACE, H5E_CANTALLOC, NULL, "can't allocate hyperslab span")
+
+    /* Copy the span's basic information */
+    ret_value->low = low;
+    ret_value->high = high;
+    ret_value->down = down;
+    ret_value->next = next;
+
+    /* Increment the reference count of the 'down span' if there is one */
+    if(ret_value->down)
+        ret_value->down->count++;
+
+done:
+    FUNC_LEAVE_NOAPI(ret_value)
+} /* end H5S__hyper_new_span() */
+
+
+/*--------------------------------------------------------------------------
+ NAME
+    H5S__hyper_new_span_info
+ PURPOSE
+    Make a new hyperslab span info node
+ USAGE
+    H5S_hyper_span_info_t *H5S__hyper_new_span_info(rank)
+        unsigned rank;          IN: Rank of span info, in selection
+ RETURNS
+    Pointer to new span node info on success, NULL on failure
+ DESCRIPTION
+    Allocate and initialize a new hyperslab span info node of a given rank,
+    setting up the low & high bound array pointers.
+ GLOBAL VARIABLES
+ COMMENTS, BUGS, ASSUMPTIONS
+    Note that this uses the C99 "flexible array member" feature.
+ EXAMPLES
+ REVISION LOG
+--------------------------------------------------------------------------*/
+static H5S_hyper_span_info_t *
+H5S__hyper_new_span_info(unsigned rank)
+{
+    H5S_hyper_span_info_t *ret_value = NULL;         /* Return value */
+
+    FUNC_ENTER_STATIC
+
+    /* Sanity check */
+    HDassert(rank > 0);
+    HDassert(rank <= H5S_MAX_RANK);
+
+    /* Allocate a new span info node */
+    if(NULL == (ret_value = (H5S_hyper_span_info_t *)H5FL_ARR_CALLOC(hbounds_t, rank * 2)))
+        HGOTO_ERROR(H5E_DATASPACE, H5E_CANTALLOC, NULL, "can't allocate hyperslab span info")
+
+    /* Set low & high bound pointers into the 'bounds' array */
+    ret_value->low_bounds = ret_value->bounds;
+    ret_value->high_bounds = &ret_value->bounds[rank];
+
+done:
+    FUNC_LEAVE_NOAPI(ret_value)
+} /* end H5S__hyper_new_span_info() */
 
 
 /*--------------------------------------------------------------------------
@@ -1305,8 +2855,11 @@ H5S__hyper_span_scratch(H5S_hyper_span_info_t *spans)
  PURPOSE
     Helper routine to copy a hyperslab span tree
  USAGE
-    H5S_hyper_span_info_t * H5S__hyper_copy_span_helper(spans)
+    H5S_hyper_span_info_t * H5S__hyper_copy_span_helper(spans, rank, op_info_i, op_gen)
         H5S_hyper_span_info_t *spans;   IN: Span tree to copy
+        unsigned rank;                  IN: Rank of span tree
+        unsigned op_info_i;             IN: Index of op info to use
+        uint64_t op_gen;                IN: Operation generation
  RETURNS
     Pointer to the copied span tree on success, NULL on failure
  DESCRIPTION
@@ -1317,7 +2870,8 @@ H5S__hyper_span_scratch(H5S_hyper_span_info_t *spans)
  REVISION LOG
 --------------------------------------------------------------------------*/
 static H5S_hyper_span_info_t *
-H5S__hyper_copy_span_helper(H5S_hyper_span_info_t *spans)
+H5S__hyper_copy_span_helper(H5S_hyper_span_info_t *spans, unsigned rank,
+    unsigned op_info_i, uint64_t op_gen)
 {
     H5S_hyper_span_t *span;         /* Hyperslab span */
     H5S_hyper_span_t *new_span;     /* Temporary hyperslab span */
@@ -1329,26 +2883,30 @@ H5S__hyper_copy_span_helper(H5S_hyper_span_info_t *spans)
 
     /* Sanity checks */
     HDassert(spans);
-    HDassert(spans->scratch != (H5S_hyper_span_info_t *)~((size_t)NULL));
 
     /* Check if the span tree was already copied */
-    if(spans->scratch != NULL) {
+    if(spans->op_info[op_info_i].op_gen == op_gen) {
         /* Just return the value of the already copied span tree */
-        ret_value = spans->scratch;
+        ret_value = spans->op_info[op_info_i].u.copied;
 
         /* Increment the reference count of the span tree */
         ret_value->count++;
     } /* end if */
     else {
         /* Allocate a new span_info node */
-        if(NULL == (ret_value = H5FL_CALLOC(H5S_hyper_span_info_t)))
+        if(NULL == (ret_value = H5S__hyper_new_span_info(rank)))
             HGOTO_ERROR(H5E_DATASPACE, H5E_CANTALLOC, NULL, "can't allocate hyperslab span info")
 
-        /* Copy the span_info information */
+        /* Set the non-zero span_info information */
+        H5MM_memcpy(ret_value->low_bounds, spans->low_bounds, rank * sizeof(hsize_t));
+        H5MM_memcpy(ret_value->high_bounds, spans->high_bounds, rank * sizeof(hsize_t));
         ret_value->count = 1;
 
-        /* Set the scratch pointer in the node being copied to the newly allocated node */
-        spans->scratch = ret_value;
+        /* Set the operation generation for the span info, to avoid future copies */
+        spans->op_info[op_info_i].op_gen = op_gen;
+
+        /* Set the 'copied' pointer in the node being copied to the newly allocated node */
+        spans->op_info[op_info_i].u.copied = ret_value;
 
         /* Copy over the nodes in the span list */
         span = spans->head;
@@ -1364,12 +2922,9 @@ H5S__hyper_copy_span_helper(H5S_hyper_span_info_t *spans)
             else
                 prev_span->next = new_span;
 
-            /* Copy the pstride */
-            new_span->pstride = span->pstride;
-
             /* Recurse to copy the 'down' spans, if there are any */
             if(span->down != NULL) {
-                if(NULL == (new_down = H5S__hyper_copy_span_helper(span->down)))
+                if(NULL == (new_down = H5S__hyper_copy_span_helper(span->down, rank - 1, op_info_i, op_gen)))
                     HGOTO_ERROR(H5E_DATASPACE, H5E_CANTCOPY, NULL, "can't copy hyperslab spans")
                 new_span->down = new_down;
             } /* end if */
@@ -1380,6 +2935,9 @@ H5S__hyper_copy_span_helper(H5S_hyper_span_info_t *spans)
             /* Advance to next span */
             span = span->next;
         } /* end while */
+
+        /* Retain a pointer to the last span */
+        ret_value->tail = prev_span;
     } /* end else */
 
 done:
@@ -1393,8 +2951,9 @@ done:
  PURPOSE
     Copy a hyperslab span tree
  USAGE
-    H5S_hyper_span_info_t * H5S__hyper_copy_span(span_info)
+    H5S_hyper_span_info_t * H5S__hyper_copy_span(span_info, rank)
         H5S_hyper_span_info_t *span_info;       IN: Span tree to copy
+        unsigned rank;                          IN: Rank of span tree
  RETURNS
     Pointer to the copied span tree on success, NULL on failure
  DESCRIPTION
@@ -1407,21 +2966,25 @@ done:
  REVISION LOG
 --------------------------------------------------------------------------*/
 static H5S_hyper_span_info_t *
-H5S__hyper_copy_span(H5S_hyper_span_info_t *spans)
+H5S__hyper_copy_span(H5S_hyper_span_info_t *spans, unsigned rank)
 {
+    uint64_t op_gen;            /* Operation generation value */
     H5S_hyper_span_info_t *ret_value = NULL;    /* Return value */
 
     FUNC_ENTER_STATIC
 
+    /* Sanity check */
     HDassert(spans);
 
+    /* Acquire an operation generation value for this operation */
+    op_gen = H5S__hyper_get_op_gen();
+
     /* Copy the hyperslab span tree */
-    if(NULL == (ret_value = H5S__hyper_copy_span_helper(spans)))
+    /* Always use op_info[0] since we own this op_info, so there can be no
+     * simultaneous operations */
+    if(NULL == (ret_value = H5S__hyper_copy_span_helper(spans, rank, 0, op_gen)))
         HGOTO_ERROR(H5E_DATASPACE, H5E_CANTCOPY, NULL, "can't copy hyperslab span tree")
 
-    /* Reset the scratch pointers for the next routine which needs them */
-    H5S__hyper_span_scratch(spans);
-
 done:
     FUNC_LEAVE_NOAPI(ret_value)
 } /* end H5S__hyper_copy_span() */
@@ -1449,25 +3012,28 @@ done:
 static H5_ATTR_PURE hbool_t
 H5S__hyper_cmp_spans(const H5S_hyper_span_info_t *span_info1, const H5S_hyper_span_info_t *span_info2)
 {
-    hbool_t ret_value = FALSE;    /* Return value */
+    hbool_t ret_value = TRUE;   /* Return value */
 
     FUNC_ENTER_STATIC_NOERR
 
-    /* Check for redundant comparison */
-    if(span_info1 == span_info2)
-        ret_value = TRUE;
-    else {
-        const H5S_hyper_span_t *span1;
-        const H5S_hyper_span_t *span2;
-
-        /* Check for both spans being NULL */
-        if(span_info1 == NULL && span_info2 == NULL)
-            ret_value = TRUE;
+    /* Check for redundant comparison (or both spans being NULL) */
+    if(span_info1 != span_info2) {
+        /* Check for one span being NULL */
+        if(span_info1 == NULL || span_info2 == NULL)
+            HGOTO_DONE(FALSE)
         else {
-            /* Check for one span being NULL */
-            if(span_info1 == NULL || span_info2 == NULL)
-                ret_value = FALSE;
+            /* Compare low & high bounds for this span list */
+            /* (Could compare lower dimensions also, but not certain if
+             *      that's worth it. - QAK, 2019/01/23)
+             */
+            if(span_info1->low_bounds[0] != span_info2->low_bounds[0])
+                HGOTO_DONE(FALSE)
+            else if(span_info1->high_bounds[0] != span_info2->high_bounds[0])
+                HGOTO_DONE(FALSE)
             else {
+                const H5S_hyper_span_t *span1;
+                const H5S_hyper_span_t *span2;
+
                 /* Get the pointers to the actual lists of spans */
                 span1 = span_info1->head;
                 span2 = span_info2->head;
@@ -1479,28 +3045,20 @@ H5S__hyper_cmp_spans(const H5S_hyper_span_info_t *span_info1, const H5S_hyper_sp
                 /* infinite loop which must be broken out of */
                 while(1) {
                     /* Check for both spans being NULL */
-                    if(span1 == NULL && span2 == NULL) {
-                        ret_value = TRUE;
-                        break;
-                    } /* end if */
+                    if(span1 == NULL && span2 == NULL)
+                        HGOTO_DONE(TRUE)
                     else {
                         /* Check for one span being NULL */
-                        if(span1 == NULL || span2 == NULL) {
-                            ret_value = FALSE;
-                            break;
-                        } /* end if */
+                        if(span1 == NULL || span2 == NULL)
+                            HGOTO_DONE(FALSE)
                         else {
                             /* Check if the actual low & high span information is the same */
-                            if(span1->low != span2->low || span1->high != span2->high) {
-                                ret_value = FALSE;
-                                break;
-                            } /* end if */
+                            if(span1->low != span2->low || span1->high != span2->high)
+                                HGOTO_DONE(FALSE)
                             else {
-                                if(span1->down != NULL || span2 != NULL) {
-                                    if(!H5S__hyper_cmp_spans(span1->down, span2->down)) {
-                                        ret_value = FALSE;
-                                        break;
-                                    } /* end if */
+                                if(span1->down != NULL || span2->down != NULL) {
+                                    if(!H5S__hyper_cmp_spans(span1->down, span2->down))
+                                        HGOTO_DONE(FALSE)
                                     else {
                                         /* Keep going... */
                                     } /* end else */
@@ -1518,8 +3076,11 @@ H5S__hyper_cmp_spans(const H5S_hyper_span_info_t *span_info1, const H5S_hyper_sp
                 } /* end while */
             } /* end else */
         } /* end else */
-    } /* end else */
+    } /* end if */
 
+    /* Fall through, with default return value of 'TRUE' if spans were already visited */
+
+done:
     FUNC_LEAVE_NOAPI(ret_value)
 } /* end H5S__hyper_cmp_spans() */
 
@@ -1530,10 +3091,10 @@ H5S__hyper_cmp_spans(const H5S_hyper_span_info_t *span_info1, const H5S_hyper_sp
  PURPOSE
     Free a hyperslab span info node
  USAGE
-    herr_t H5S__hyper_free_span_info(span_info)
+    void H5S__hyper_free_span_info(span_info)
         H5S_hyper_span_info_t *span_info;      IN: Span info node to free
  RETURNS
-    Non-negative on success, negative on failure
+    None
  DESCRIPTION
     Free a hyperslab span info node, along with all the span nodes and the
     'down spans' from the nodes, if reducing their reference count to zero
@@ -1543,13 +3104,10 @@ H5S__hyper_cmp_spans(const H5S_hyper_span_info_t *span_info1, const H5S_hyper_sp
  EXAMPLES
  REVISION LOG
 --------------------------------------------------------------------------*/
-static herr_t
+static void
 H5S__hyper_free_span_info(H5S_hyper_span_info_t *span_info)
 {
-    H5S_hyper_span_t *span, *next_span;
-    herr_t      ret_value = SUCCEED;    /* Return value */
-
-    FUNC_ENTER_STATIC
+    FUNC_ENTER_STATIC_NOERR
 
     /* Sanity check */
     HDassert(span_info);
@@ -1559,22 +3117,28 @@ H5S__hyper_free_span_info(H5S_hyper_span_info_t *span_info)
 
     /* Free the span tree if the reference count drops to zero */
     if(span_info->count == 0) {
+        H5S_hyper_span_t *span;     /* Pointer to spans to iterate over */
 
         /* Work through the list of spans pointed to by this 'info' node */
         span = span_info->head;
         while(span != NULL) {
+            H5S_hyper_span_t *next_span;     /* Pointer to next span to iterate over */
+
+            /* Keep a pointer to the next span */
             next_span = span->next;
-            if(H5S__hyper_free_span(span) < 0)
-                HGOTO_ERROR(H5E_INTERNAL, H5E_CANTFREE, FAIL, "failed to release hyperslab span")
+
+            /* Free the current span */
+            H5S__hyper_free_span(span);
+
+            /* Advance to next span */
             span = next_span;
         } /* end while */
 
         /* Free this span info */
-        span_info = H5FL_FREE(H5S_hyper_span_info_t, span_info);
+        span_info = (H5S_hyper_span_info_t *)H5FL_ARR_FREE(hbounds_t, span_info);
     } /* end if */
 
-done:
-    FUNC_LEAVE_NOAPI(ret_value)
+    FUNC_LEAVE_NOAPI_VOID
 } /* end H5S__hyper_free_span_info() */
 
 
@@ -1584,10 +3148,10 @@ done:
  PURPOSE
     Free a hyperslab span node
  USAGE
-    herr_t H5S__hyper_free_span(span)
+    void H5S__hyper_free_span(span)
         H5S_hyper_span_t *span;      IN: Span node to free
  RETURNS
-    Non-negative on success, negative on failure
+    None
  DESCRIPTION
     Free a hyperslab span node, along with the 'down spans' from the node,
     if reducing their reference count to zero indicates it is appropriate to
@@ -1597,26 +3161,22 @@ done:
  EXAMPLES
  REVISION LOG
 --------------------------------------------------------------------------*/
-static herr_t
+static void
 H5S__hyper_free_span(H5S_hyper_span_t *span)
 {
-    herr_t ret_value = SUCCEED;
-
-    FUNC_ENTER_STATIC
+    FUNC_ENTER_STATIC_NOERR
 
     /* Sanity check */
     HDassert(span);
 
     /* Decrement the reference count of the 'down spans', freeing them if appropriate */
     if(span->down != NULL)
-        if(H5S__hyper_free_span_info(span->down) < 0)
-            HGOTO_ERROR(H5E_INTERNAL, H5E_CANTFREE, FAIL, "failed to release hyperslab span tree")
+        H5S__hyper_free_span_info(span->down);
 
     /* Free this span */
     span = H5FL_FREE(H5S_hyper_span_t, span);
 
-done:
-    FUNC_LEAVE_NOAPI(ret_value)
+    FUNC_LEAVE_NOAPI_VOID
 } /* end H5S__hyper_free_span() */
 
 
@@ -1668,15 +3228,8 @@ H5S__hyper_copy(H5S_t *dst, const H5S_t *src, hbool_t share_selection)
 
     /* Copy the hyperslab information */
     dst_hslab->diminfo_valid = src_hslab->diminfo_valid;
-    if(src_hslab->diminfo_valid == H5S_DIMINFO_VALID_YES) {
-        size_t u;       /* Local index variable */
-
-        for(u=0; u<src->extent.rank; u++) {
-            dst_hslab->diminfo.opt[u]=src_hslab->diminfo.opt[u];
-            dst_hslab->diminfo.app[u]=src_hslab->diminfo.app[u];
-        } /* end for */
-    } /* end if */
-    dst->select.sel_info.hslab->span_lst = src->select.sel_info.hslab->span_lst;
+    if(src_hslab->diminfo_valid == H5S_DIMINFO_VALID_YES)
+        H5MM_memcpy(&dst_hslab->diminfo, &src_hslab->diminfo, sizeof(H5S_hyper_diminfo_t));
 
     /* Check if there is hyperslab span information to copy */
     /* (Regular hyperslab information is copied with the selection structure) */
@@ -1688,7 +3241,7 @@ H5S__hyper_copy(H5S_t *dst, const H5S_t *src, hbool_t share_selection)
         } /* end if */
         else
             /* Copy the hyperslab span information */
-            dst->select.sel_info.hslab->span_lst = H5S__hyper_copy_span(src->select.sel_info.hslab->span_lst);
+            dst->select.sel_info.hslab->span_lst = H5S__hyper_copy_span(src->select.sel_info.hslab->span_lst, src->extent.rank);
     } /* end if */
     else
         dst->select.sel_info.hslab->span_lst = NULL;
@@ -1704,18 +3257,16 @@ done:
 
 /*--------------------------------------------------------------------------
  NAME
-    H5S__hyper_is_valid_helper
+    H5S__hyper_is_valid
  PURPOSE
     Check whether the selection fits within the extent, with the current
     offset defined.
  USAGE
-    hbool_t H5S__hyper_is_valid_helper(spans, offset, rank);
-        const H5S_hyper_span_info_t *spans; IN: Pointer to current hyperslab span tree
-        const hssize_t *offset;             IN: Pointer to offset array
-        const hsize_t *size;                IN: Pointer to size array
-        hsize_t rank;                       IN: Current rank looking at
+    htri_t H5S__hyper_is_valid(space);
+        H5S_t *space;             IN: Dataspace pointer to query
  RETURNS
-    TRUE if the selection fits within the extent, FALSE if it does not
+    TRUE if the selection fits within the extent, FALSE if it does not and
+        Negative on an error.
  DESCRIPTION
     Determines if the current selection at the current offset fits within the
     extent for the dataspace.
@@ -1724,109 +3275,111 @@ done:
  EXAMPLES
  REVISION LOG
 --------------------------------------------------------------------------*/
-static hbool_t
-H5S__hyper_is_valid_helper(const H5S_hyper_span_info_t *spans, const hssize_t *offset,
-    const hsize_t *size)
+static htri_t
+H5S__hyper_is_valid(const H5S_t *space)
 {
-    H5S_hyper_span_t *curr;     /* Hyperslab information nodes */
-    hbool_t ret_value = TRUE;   /* Return value */
+    const hsize_t *low_bounds, *high_bounds;    /* Pointers to the correct pair of low & high bounds */
+    unsigned u;                    /* Counter */
+    htri_t ret_value = TRUE;      /* return value */
 
     FUNC_ENTER_STATIC_NOERR
 
-    HDassert(spans);
-    HDassert(offset);
-    HDassert(size);
+    HDassert(space);
 
-    /* Check each point to determine whether selection + offset is within extent */
-    curr = spans->head;
-    while(curr != NULL) {
-        /* Check if an offset has been defined */
-        /* Bounds check the selected point + offset against the extent */
-        if((((hssize_t)curr->low + *offset) >= (hssize_t)*size)
-                || (((hssize_t)curr->low + *offset) < 0)
-                || (((hssize_t)curr->high + *offset) >= (hssize_t)*size)
-                || (((hssize_t)curr->high + *offset) < 0))
-            HGOTO_DONE(FALSE)
+    /* Check for unlimited selection */
+    if(space->select.sel_info.hslab->unlim_dim >= 0)
+        HGOTO_DONE(FALSE)
 
-        /* Recurse if this node has down spans */
-        if(curr->down != NULL)
-            if(!H5S__hyper_is_valid_helper(curr->down, offset + 1, size + 1))
-                HGOTO_DONE(FALSE)
+    /* Check which set of low & high bounds we should be using */
+    if(space->select.sel_info.hslab->diminfo_valid == H5S_DIMINFO_VALID_YES) {
+        low_bounds = space->select.sel_info.hslab->diminfo.low_bounds;
+        high_bounds = space->select.sel_info.hslab->diminfo.high_bounds;
+    } /* end if */
+    else {
+        low_bounds = space->select.sel_info.hslab->span_lst->low_bounds;
+        high_bounds = space->select.sel_info.hslab->span_lst->high_bounds;
+    } /* end else */
 
-        /* Advance to next node */
-        curr = curr->next;
-    } /* end while */
+    /* Check each dimension */
+    for(u = 0; u < space->extent.rank; u++) {
+        /* Bounds check the selected point + offset against the extent */
+        if(((hssize_t)low_bounds[u] + space->select.offset[u]) < 0)
+            HGOTO_DONE(FALSE)
+        if((high_bounds[u] + (hsize_t)space->select.offset[u]) >= space->extent.size[u])
+            HGOTO_DONE(FALSE)
+    } /* end for */
 
 done:
     FUNC_LEAVE_NOAPI(ret_value)
-} /* end H5S__hyper_is_valid_helper() */
+} /* end H5S__hyper_is_valid() */
 
 
 /*--------------------------------------------------------------------------
  NAME
-    H5S__hyper_is_valid
+    H5S__hyper_span_nblocks_helper
  PURPOSE
-    Check whether the selection fits within the extent, with the current
-    offset defined.
+    Helper routine to count the number of blocks in a span tree
  USAGE
-    htri_t H5S__hyper_is_valid(space);
-        H5S_t *space;             IN: Dataspace pointer to query
+    hsize_t H5S__hyper_span_nblocks_helper(spans, op_info_i, op_gen)
+        H5S_hyper_span_info_t *spans; IN: Hyperslab span tree to count blocks of
+        unsigned op_info_i; IN: Index of op info to use
+        uint64_t op_gen;   IN: Operation generation
  RETURNS
-    TRUE if the selection fits within the extent, FALSE if it does not and
-        Negative on an error.
+    Number of blocks in span tree on success; negative on failure
  DESCRIPTION
-    Determines if the current selection at the current offset fits within the
-    extent for the dataspace.
+    Counts the number of blocks described by the spans in a span tree.
  GLOBAL VARIABLES
  COMMENTS, BUGS, ASSUMPTIONS
  EXAMPLES
  REVISION LOG
 --------------------------------------------------------------------------*/
-static htri_t
-H5S__hyper_is_valid(const H5S_t *space)
+static hsize_t
+H5S__hyper_span_nblocks_helper(H5S_hyper_span_info_t *spans, unsigned op_info_i,
+    uint64_t op_gen)
 {
-    htri_t ret_value = TRUE;      /* return value */
+    hsize_t ret_value = 0;      /* Return value */
 
     FUNC_ENTER_STATIC_NOERR
 
-    HDassert(space);
+    /* Sanity check */
+    HDassert(spans);
 
-    /* Check for unlimited selection */
-    if(space->select.sel_info.hslab->unlim_dim >= 0)
-        HGOTO_DONE(FALSE)
+    /* Check if the span tree was already counted */
+    if(spans->op_info[op_info_i].op_gen == op_gen)
+        /* Just return the # of blocks in the already counted span tree */
+        ret_value = spans->op_info[op_info_i].u.nblocks;
+    else {      /* Count the number of elements in the span tree */
+        H5S_hyper_span_t *span;     /* Hyperslab span */
 
-    /* Check for a "regular" hyperslab selection */
-    if(H5S_DIMINFO_VALID_YES == space->select.sel_info.hslab->diminfo_valid) {
-        const H5S_hyper_dim_t *diminfo = space->select.sel_info.hslab->diminfo.opt; /* local alias for diminfo */
-        hssize_t end;      /* The high bound of a region in a dimension */
-        unsigned u;        /* Counter */
+        span = spans->head;
+        if(span->down) {
+            while(span) {
+                /* If there are down spans, add the total down span blocks */
+                ret_value += H5S__hyper_span_nblocks_helper(span->down, op_info_i, op_gen);
 
-        /* Check each dimension */
-        for(u = 0; u < space->extent.rank; u++) {
-            /* if block or count is zero, then can skip the test since */
-            /* no data point is chosen */
-            if(diminfo[u].count && diminfo[u].block) {
-                /* Bounds check the start point in this dimension */
-                if(((hssize_t)diminfo[u].start + space->select.offset[u]) < 0 ||
-                        ((hssize_t)diminfo[u].start + space->select.offset[u]) >= (hssize_t)space->extent.size[u])
-                    HGOTO_DONE(FALSE)
+                /* Advance to next span */
+                span = span->next;
+            } /* end while */
+        } /* end if */
+        else {
+            while(span) {
+                /* If there are no down spans, just count the block in this span */
+                ret_value++;
+
+                /* Advance to next span */
+                span = span->next;
+            } /* end while */
+        } /* end else */
 
-                /* Compute the largest location in this dimension */
-                end = (hssize_t)(diminfo[u].start + diminfo[u].stride * (diminfo[u].count - 1) + (diminfo[u].block - 1)) + space->select.offset[u];
+        /* Set the operation generation for this span tree, to avoid re-computing */
+        spans->op_info[op_info_i].op_gen = op_gen;
 
-                /* Bounds check the end point in this dimension */
-                if(end < 0 || end >= (hssize_t)space->extent.size[u])
-                    HGOTO_DONE(FALSE)
-            } /* end if */
-        } /* end for */
-    } /* end if */
-    else
-        /* Call the recursive routine to validate the span tree */
-        ret_value = H5S__hyper_is_valid_helper(space->select.sel_info.hslab->span_lst, space->select.offset, space->extent.size);
+        /* Hold a copy of the # of blocks */
+        spans->op_info[op_info_i].u.nblocks = ret_value;
+    } /* end else */
 
-done:
     FUNC_LEAVE_NOAPI(ret_value)
-} /* end H5S__hyper_is_valid() */
+} /* end H5S__hyper_span_nblocks_helper() */
 
 
 /*--------------------------------------------------------------------------
@@ -1836,7 +3389,7 @@ done:
     Count the number of blocks in a span tree
  USAGE
     hsize_t H5S__hyper_span_nblocks(spans)
-        const H5S_hyper_span_info_t *spans; IN: Hyperslab span tree to count elements of
+        H5S_hyper_span_info_t *spans; IN: Hyperslab span tree to count blocks of
  RETURNS
     Number of blocks in span tree on success; negative on failure
  DESCRIPTION
@@ -1847,7 +3400,7 @@ done:
  REVISION LOG
 --------------------------------------------------------------------------*/
 static hsize_t
-H5S__hyper_span_nblocks(const H5S_hyper_span_info_t *spans)
+H5S__hyper_span_nblocks(H5S_hyper_span_info_t *spans)
 {
     hsize_t ret_value = 0;      /* Return value */
 
@@ -1855,21 +3408,16 @@ H5S__hyper_span_nblocks(const H5S_hyper_span_info_t *spans)
 
     /* Count the number of elements in the span tree */
     if(spans != NULL) {
-        H5S_hyper_span_t *span;     /* Hyperslab span */
+        uint64_t op_gen;            /* Operation generation value */
 
-        span = spans->head;
-        while(span != NULL) {
-            /* If there are down spans, add the total down span blocks */
-            if(span->down != NULL)
-                ret_value += H5S__hyper_span_nblocks(span->down);
-            /* If there are no down spans, just count the block in this span */
-            else
-                ret_value++;
+        /* Acquire an operation generation value for this operation */
+        op_gen = H5S__hyper_get_op_gen();
 
-            /* Advance to next span */
-            span = span->next;
-        } /* end while */
-    } /* end else */
+        /* Count the blocks */
+        /* Always use op_info[0] since we own this op_info, so there can be no
+         * simultaneous operations */
+        ret_value = H5S__hyper_span_nblocks_helper(spans, 0, op_gen);
+    } /* end if */
 
     FUNC_LEAVE_NOAPI(ret_value)
 } /* end H5S__hyper_span_nblocks() */
@@ -1904,6 +3452,7 @@ H5S__get_select_hyper_nblocks(const H5S_t *space, hbool_t app_ref)
     HDassert(space->select.sel_info.hslab->unlim_dim < 0);
 
     /* Check for a "regular" hyperslab selection */
+    /* (No need to rebuild the dimension info yet -QAK) */
     if(space->select.sel_info.hslab->diminfo_valid == H5S_DIMINFO_VALID_YES) {
         unsigned u;                 /* Local index variable */
 
@@ -1962,10 +3511,43 @@ done:
 
 /*--------------------------------------------------------------------------
  NAME
+    H5S__hyper_get_enc_size_real
+ PURPOSE
+    Determine the size to encode the hyperslab selection info
+ USAGE
+    hssize_t H5S__hyper_get_enc_size_real(max_size, enc_size)
+        hsize_t max_size:       IN: The maximum size of the hyperslab selection info
+        unint8_t *enc_size:     OUT:The encoding size
+ RETURNS
+    The size to encode hyperslab selection info
+ DESCRIPTION
+    Determine the size by comparing "max_size" with (2^32 - 1) and (2^16 - 1).
+ GLOBAL VARIABLES
+ COMMENTS, BUGS, ASSUMPTIONS
+ EXAMPLES
+ REVISION LOG
+--------------------------------------------------------------------------*/
+static uint8_t
+H5S__hyper_get_enc_size_real(hsize_t max_size)
+{
+    uint8_t ret_value;
+
+    FUNC_ENTER_STATIC_NOERR
+
+    if(max_size > H5S_UINT32_MAX)
+        ret_value = H5S_SELECT_INFO_ENC_SIZE_8;
+    else
+        ret_value = H5S_SELECT_INFO_ENC_SIZE_4;
+
+    FUNC_LEAVE_NOAPI(ret_value)
+} /* H5S__hyper_get_enc_size_real() */
+
+
+/*--------------------------------------------------------------------------
+ NAME
     H5S__hyper_get_version_enc_size
  PURPOSE
     Determine the version and encoded size to use for encoding hyperslab selection info
-    See tables 2 & 3 in the RFC: H5Sencode/H5Sdecode Format Change
  USAGE
     hssize_t H5S__hyper_get_version_enc_size(space, block_count, version, enc_size)
         const H5S_t *space:             IN: The dataspace
@@ -1977,8 +3559,10 @@ done:
     The version and the size to encode hyperslab selection info
  DESCRIPTION
     Determine the version to use for encoding hyperslab selection info based
-    on whether the number of blocks or the selection high bounds exceeds (2^32 - 1).
-    Then determine the encoded size based on version.
+    on the following:
+    (1) the file format setting in fapl
+    (2) whether the number of blocks or selection high bounds exceeds H5S_UINT32_MAX or not
+
  GLOBAL VARIABLES
  COMMENTS, BUGS, ASSUMPTIONS
  EXAMPLES
@@ -2144,12 +3728,13 @@ done:
  PURPOSE
     Serialize the current selection into a user-provided buffer.
  USAGE
-    void H5S__hyper_serialize_helper(spans, start, end, rank, buf)
+    void H5S__hyper_serialize_helper(spans, start, end, rank, enc_size, buf)
         H5S_hyper_span_info_t *spans;   IN: Hyperslab span tree to serialize
         hssize_t start[];       IN/OUT: Accumulated start points
         hssize_t end[];         IN/OUT: Accumulated end points
         hsize_t rank;           IN: Current rank looking at
-        uint8 *buf;             OUT: Buffer to put serialized selection into
+        uint8_t enc_size        IN: Encoded size of hyperslab selection info
+        uint8_t *buf;           OUT: Buffer to put serialized selection into
  RETURNS
     None
  DESCRIPTION
@@ -2162,7 +3747,7 @@ done:
 --------------------------------------------------------------------------*/
 static void
 H5S__hyper_serialize_helper(const H5S_hyper_span_info_t *spans,
-        hsize_t *start, hsize_t *end, hsize_t rank, uint8_t **p)
+        hsize_t *start, hsize_t *end, hsize_t rank, uint8_t enc_size, uint8_t **p)
 {
     H5S_hyper_span_t *curr;     /* Pointer to current hyperslab span */
     uint8_t *pp = (*p);         /* Local pointer for decoding */
@@ -2186,26 +3771,49 @@ H5S__hyper_serialize_helper(const H5S_hyper_span_info_t *spans,
             end[rank] = curr->high;
 
             /* Recurse down to the next dimension */
-            H5S__hyper_serialize_helper(curr->down, start, end, rank + 1, &pp);
+            H5S__hyper_serialize_helper(curr->down, start, end, rank + 1, enc_size, &pp);
         } /* end if */
         else {
             hsize_t u;                  /* Index variable */
 
             /* Encode all the previous dimensions starting & ending points */
+            switch(enc_size) {
+                case H5S_SELECT_INFO_ENC_SIZE_4:
+                    /* Encode previous starting points */
+                    for(u=0; u<rank; u++)
+                        UINT32ENCODE(pp, (uint32_t)start[u]);
 
-            /* Encode previous starting points */
-            for(u = 0; u < rank; u++)
-                UINT32ENCODE(pp, (uint32_t)start[u]);
+                    /* Encode starting point for this span */
+                    UINT32ENCODE(pp, (uint32_t)curr->low);
 
-            /* Encode starting point for this span */
-            UINT32ENCODE(pp, (uint32_t)curr->low);
+                     /* Encode previous ending points */
+                    for(u=0; u<rank; u++)
+                        UINT32ENCODE(pp, (uint32_t)end[u]);
 
-            /* Encode previous ending points */
-            for(u = 0; u < rank; u++)
-                UINT32ENCODE(pp, (uint32_t)end[u]);
+                    /* Encode starting point for this span */
+                    UINT32ENCODE(pp, (uint32_t)curr->high);
+                    break;
+
+                case H5S_SELECT_INFO_ENC_SIZE_8:
+                    /* Encode previous starting points */
+                    for(u=0; u<rank; u++)
+                        UINT64ENCODE(pp, (uint64_t)start[u]);
 
-            /* Encode starting point for this span */
-            UINT32ENCODE(pp, (uint32_t)curr->high);
+                    /* Encode starting point for this span */
+                    UINT64ENCODE(pp, (uint64_t)curr->low);
+
+                    /* Encode previous ending points */
+                    for(u=0; u<rank; u++)
+                        UINT64ENCODE(pp, (uint64_t)end[u]);
+
+                    /* Encode starting point for this span */
+                    UINT64ENCODE(pp, (uint64_t)curr->high);
+                    break;
+
+                default:
+                    HDassert(0 && "Unknown enc size?!?");
+
+            } /* end switch */
         } /* end else */
 
         /* Advance to next node */
@@ -2256,8 +3864,8 @@ H5S__hyper_serialize(const H5S_t *space, uint8_t **p)
     hsize_t block_count = 0;    /* block counter for regular hyperslabs */
     unsigned fast_dim;      /* Rank of the fastest changing dimension for the dataspace */
     unsigned ndims;         /* Rank of the dataspace */
-    unsigned i, u;          /* Local counting variable */
-    int done;               /* Whether we are done with the iteration */
+    unsigned u;             /* Local counting variable */
+    hbool_t complete = FALSE;   /* Whether we are done with the iteration */
     hbool_t is_regular;     /* Whether selection is regular */
     uint8_t enc_size;       /* Encoded size */
     herr_t ret_value = SUCCEED; /* return value */
@@ -2302,27 +3910,37 @@ H5S__hyper_serialize(const H5S_t *space, uint8_t **p)
     /* Encode number of dimensions */
     UINT32ENCODE(pp, (uint32_t)ndims);
 
-    /* Check for a "regular" hyperslab selection */
     if(is_regular) {
-
-        /* If flags indicates a regular hyperslab or unlimited dimension, encode diminfo.opt */
         if(version ==  H5S_HYPER_VERSION_2) {
-
             HDassert(H5S_UNLIMITED == HSIZE_UNDEF);
-            HDassert(enc_size == H5S_SELECT_INFO_ENC_SIZE_8);
 
             /* Iterate over dimensions */
             /* Encode start/stride/block/count */
-            for(i = 0; i < space->extent.rank; i++) {
-                UINT64ENCODE(pp, diminfo[i].start);
-                UINT64ENCODE(pp, diminfo[i].stride);
-                UINT64ENCODE(pp, diminfo[i].count);
-                UINT64ENCODE(pp, diminfo[i].block);
-            } /* end for */
-            len += (4 * space->extent.rank * 8);
-        } else {
+            switch(enc_size) {
+                case H5S_SELECT_INFO_ENC_SIZE_8:
+                    HDassert(version == H5S_HYPER_VERSION_2);
+                    for(u = 0; u < space->extent.rank; u++) {
+                        UINT64ENCODE(pp, diminfo[u].start);
+                        UINT64ENCODE(pp, diminfo[u].stride);
+                        if(diminfo[u].count == H5S_UNLIMITED)
+                            UINT64ENCODE(pp, H5S_UINT64_MAX)
+                        else
+                            UINT64ENCODE(pp, diminfo[u].count)
+                        if(diminfo[u].block == H5S_UNLIMITED)
+                            UINT64ENCODE(pp, H5S_UINT64_MAX)
+                        else
+                            UINT64ENCODE(pp, diminfo[u].block)
+                    } /* end for */
+                    if(version == H5S_HYPER_VERSION_2)
+                        len += (4 * space->extent.rank * 8);
+                    break;
+                default:
+                    HGOTO_ERROR(H5E_DATASPACE, H5E_UNSUPPORTED, FAIL, "unknown offset info size for hyperslab")
+                    break;
+            } /* end switch */
+        } /* end if */
+        else {
             HDassert(version == H5S_HYPER_VERSION_1);
-            HDassert(enc_size == H5S_SELECT_INFO_ENC_SIZE_4);
 
             /* Set some convienence values */
             fast_dim = ndims - 1;
@@ -2340,11 +3958,8 @@ H5S__hyper_serialize(const H5S_t *space, uint8_t **p)
                 offset[u] = diminfo[u].start;
             } /* end for */
 
-            /* We're not done with the iteration */
-            done = FALSE;
-
             /* Go iterate over the hyperslabs */
-            while(done == FALSE) {
+            while(complete == FALSE) {
                 /* Iterate over the blocks in the fastest dimension */
                 while(tmp_count[fast_dim] > 0) {
                     /* Add 8 bytes times the rank for each hyperslab selected */
@@ -2374,7 +3989,7 @@ H5S__hyper_serialize(const H5S_t *space, uint8_t **p)
 
                     /* Bubble up the decrement to the slower changing dimensions */
                     temp_dim = (int)fast_dim - 1;
-                    while(temp_dim >= 0 && done == FALSE) {
+                    while(temp_dim >= 0 && complete == FALSE) {
                         /* Decrement the block count */
                         tmp_count[temp_dim]--;
 
@@ -2384,7 +3999,7 @@ H5S__hyper_serialize(const H5S_t *space, uint8_t **p)
 
                         /* Check for getting out of iterator */
                         if(temp_dim == 0)
-                            done = TRUE;
+                            complete = TRUE;
 
                         /* Reset the block count in this dimension */
                         tmp_count[temp_dim] = diminfo[temp_dim].count;
@@ -2400,24 +4015,31 @@ H5S__hyper_serialize(const H5S_t *space, uint8_t **p)
                 for(u = 0; u < ndims; u++)
                     offset[u] = diminfo[u].start + diminfo[u].stride * (diminfo[u].count - tmp_count[u]);
             } /* end while */
-        } /* end if */
-    }
+        } /* end else */
+    } /* end if */
     else { /* irregular */
-        HDassert(version == H5S_HYPER_VERSION_1);
-        HDassert(enc_size == H5S_SELECT_INFO_ENC_SIZE_4);
-
         /* Encode number of hyperslabs */
-        H5_CHECK_OVERFLOW(block_count, hsize_t, uint32_t);
-        UINT32ENCODE(pp, (uint32_t)block_count);
+        switch(enc_size) {
+            case H5S_SELECT_INFO_ENC_SIZE_4:
+                HDassert(version == H5S_HYPER_VERSION_1);
+                H5_CHECK_OVERFLOW(block_count, hsize_t, uint32_t);
+                UINT32ENCODE(pp, (uint32_t)block_count);
+                break;
 
-        len+=4; /* block_count */
+            default:
+                HGOTO_ERROR(H5E_DATASPACE, H5E_UNSUPPORTED, FAIL, "unknown offset info size for hyperslab")
+                break;
+        } /* end switch */
 
-        /* Add 8 bytes times the rank for each hyperslab selected */
-        H5_CHECK_OVERFLOW((8 * ndims * block_count), hsize_t, size_t);
-        len += (uint32_t)(8 * ndims * block_count);
+        if(version == H5S_HYPER_VERSION_1) {
+            len += 4; /* block_count */
 
-        /* Encode each hyperslab in selection */
-        H5S__hyper_serialize_helper(space->select.sel_info.hslab->span_lst, start, end, (hsize_t)0, &pp);
+            /* Add 8 bytes times the rank for each hyperslab selected */
+            H5_CHECK_OVERFLOW((8 * ndims * block_count), hsize_t, size_t);
+            len += (uint32_t)(8 * ndims * block_count);
+        } /* end if */
+
+        H5S__hyper_serialize_helper(space->select.sel_info.hslab->span_lst, start, end, (hsize_t)0, enc_size, &pp);
     } /* end else */
 
     /* Encode length */
@@ -2459,14 +4081,15 @@ H5S__hyper_deserialize(H5S_t **space, const uint8_t **p)
     H5S_t *tmp_space = NULL;        /* Pointer to actual dataspace to use,
                                        either *space or a newly allocated one */
     hsize_t dims[H5S_MAX_RANK];     /* Dimenion sizes */
-    hsize_t start[H5S_MAX_RANK];    /* Hyperslab start information */
-    hsize_t block[H5S_MAX_RANK];    /* Hyperslab block information */
-    uint32_t version;               /* Version number */        /* Encoded size */
+    hsize_t start[H5S_MAX_RANK];    /* hyperslab start information */
+    hsize_t block[H5S_MAX_RANK];    /* hyperslab block information */
+    uint32_t version;               /* Version number */
     uint8_t flags = 0;              /* Flags */
-    unsigned rank;                  /* Rank of points */
+    uint8_t enc_size = 0;           /* Encoded size of selection info */
+    unsigned rank;                  /* rank of points */
     const uint8_t *pp;              /* Local pointer for decoding */
     unsigned u;                     /* Local counting variable */
-    herr_t ret_value = FAIL;        /* Return value */
+    herr_t ret_value=FAIL;          /* return value */
 
     FUNC_ENTER_STATIC
 
@@ -2499,10 +4122,21 @@ H5S__hyper_deserialize(H5S_t **space, const uint8_t **p)
 
         /* Skip over the remainder of the header */
         pp += 4;
+        enc_size = H5S_SELECT_INFO_ENC_SIZE_8;
+
+         /* Check for unknown flags */
+        if(flags & ~H5S_SELECT_FLAG_BITS)
+            HGOTO_ERROR(H5E_DATASPACE, H5E_CANTLOAD, FAIL, "unknown flag for selection")
     }
-    else
+    else {
         /* Skip over the remainder of the header */
         pp += 8;
+        enc_size = H5S_SELECT_INFO_ENC_SIZE_4;
+     } /* end else */
+
+     /* Check encoded */
+     if(enc_size & ~H5S_SELECT_INFO_ENC_SIZE_BITS)
+        HGOTO_ERROR(H5E_DATASPACE, H5E_CANTLOAD, FAIL, "unknown size of point/offset info for selection")
 
     /* Decode the rank of the point selection */
     UINT32DECODE(pp,rank);
@@ -2526,14 +4160,42 @@ H5S__hyper_deserialize(H5S_t **space, const uint8_t **p)
         HDassert(H5S_UNLIMITED == HSIZE_UNDEF);
         HDassert(version >= H5S_HYPER_VERSION_2);
 
-        /* Iterate over dimensions */
-        for(u = 0; u < rank; u++) {
-            /* Decode start/stride/block/count */
-            UINT64DECODE(pp, start[u]);
-            UINT64DECODE(pp, stride[u]);
-            UINT64DECODE(pp, count[u]);
-            UINT64DECODE(pp, block[u]);
-        } /* end for */
+         /* Decode start/stride/block/count */
+        switch(enc_size) {
+            case H5S_SELECT_INFO_ENC_SIZE_4:
+                for(u = 0; u < tmp_space->extent.rank; u++) {
+                    UINT32DECODE(pp, start[u]);
+                    UINT32DECODE(pp, stride[u]);
+
+                    UINT32DECODE(pp, count[u]);
+                    if((uint32_t)count[u] == H5S_UINT32_MAX)
+                        count[u] = H5S_UNLIMITED;
+
+                    UINT32DECODE(pp, block[u]);
+                    if((uint32_t)block[u] == H5S_UINT32_MAX)
+                        block[u] = H5S_UNLIMITED;
+                } /* end for */
+                break;
+
+            case H5S_SELECT_INFO_ENC_SIZE_8:
+                for(u = 0; u < tmp_space->extent.rank; u++) {
+                    UINT64DECODE(pp, start[u]);
+                    UINT64DECODE(pp, stride[u]);
+
+                    UINT64DECODE(pp, count[u]);
+                    if((uint64_t)count[u] == H5S_UINT64_MAX)
+                        count[u] = H5S_UNLIMITED;
+
+                    UINT64DECODE(pp, block[u]);
+                    if((uint64_t)block[u] == H5S_UINT64_MAX)
+                        block[u] = H5S_UNLIMITED;
+                } /* end for */
+                break;
+
+            default:
+                HGOTO_ERROR(H5E_DATASPACE, H5E_UNSUPPORTED, FAIL, "unknown offset info size for hyperslab")
+                break;
+        } /* end switch */
 
         /* Select the hyperslab to the current selection */
         if((ret_value = H5S_select_hyperslab(tmp_space, H5S_SELECT_SET, start, stride, count, block)) < 0)
@@ -2549,21 +4211,46 @@ H5S__hyper_deserialize(H5S_t **space, const uint8_t **p)
         size_t num_elem;        /* Number of elements in selection */
         unsigned v;             /* Local counting variable */
 
-        /* Decode the number of points */
-        UINT32DECODE(pp, num_elem);
+        /* Decode the number of blocks */
+        switch(enc_size) {
+            case H5S_SELECT_INFO_ENC_SIZE_4:
+                UINT32DECODE(pp, num_elem);
+                break;
+
+            case H5S_SELECT_INFO_ENC_SIZE_8:
+                UINT64DECODE(pp, num_elem);
+                break;
+
+            default:
+                HGOTO_ERROR(H5E_DATASPACE, H5E_UNSUPPORTED, FAIL, "unknown offset info size for hyperslab")
+                break;
+        } /* end switch */
 
         /* Set the count & stride for all blocks */
         stride = count = H5S_hyper_ones_g;
 
         /* Retrieve the coordinates from the buffer */
         for(u = 0; u < num_elem; u++) {
-            /* Decode the starting points */
-            for(tstart = start, v = 0; v < rank; v++, tstart++)
-                UINT32DECODE(pp, *tstart);
+            /* Decode the starting and ending points */
+            switch(enc_size) {
+                case H5S_SELECT_INFO_ENC_SIZE_4:
+                    for(tstart = start,v = 0; v < rank; v++, tstart++)
+                        UINT32DECODE(pp, *tstart);
+                    for(tend = end, v = 0; v < rank; v++, tend++)
+                        UINT32DECODE(pp, *tend);
+                    break;
 
-            /* Decode the ending points */
-            for(tend = end, v = 0; v < rank; v++, tend++)
-                UINT32DECODE(pp, *tend);
+                case H5S_SELECT_INFO_ENC_SIZE_8:
+                    for(tstart = start, v = 0; v < rank; v++, tstart++)
+                        UINT64DECODE(pp, *tstart);
+                    for(tend = end, v = 0; v < rank; v++, tend++)
+                        UINT64DECODE(pp, *tend);
+                    break;
+
+                default:
+                    HGOTO_ERROR(H5E_DATASPACE, H5E_UNSUPPORTED, FAIL, "unknown offset info size for hyperslab")
+                    break;
+            } /* end switch */
 
             /* Change the ending points into blocks */
             for(tblock = block, tstart = start, tend = end, v = 0; v < rank; v++, tstart++, tend++, tblock++)
@@ -2631,7 +4318,6 @@ H5S__hyper_span_blocklist(const H5S_hyper_span_info_t *spans, hsize_t start[],
     hsize_t **buf)
 {
     const H5S_hyper_span_t *curr;     /* Pointer to current hyperslab span */
-    hsize_t u;                  /* Index variable */
     herr_t ret_value = SUCCEED; /* return value */
 
     FUNC_ENTER_STATIC
@@ -2669,19 +4355,19 @@ H5S__hyper_span_blocklist(const H5S_hyper_span_info_t *spans, hsize_t start[],
                 /* Encode all the previous dimensions starting & ending points */
 
                 /* Copy previous starting points */
-                for(u = 0; u < rank; u++, (*buf)++)
-                    H5MM_memcpy(*buf, &start[u], sizeof(hsize_t));
+                H5MM_memcpy(*buf, start, rank * sizeof(hsize_t));
+                (*buf) += rank;
 
                 /* Copy starting point for this span */
-                H5MM_memcpy(*buf, &curr->low, sizeof(hsize_t));
+                **buf = curr->low;
                 (*buf)++;
 
                 /* Copy previous ending points */
-                for(u = 0; u < rank; u++, (*buf)++)
-                    H5MM_memcpy(*buf, &end[u], sizeof(hsize_t));
+                H5MM_memcpy(*buf, end, rank * sizeof(hsize_t));
+                (*buf) += rank;
 
-                /* Copy starting point for this span */
-                H5MM_memcpy(*buf, &curr->high, sizeof(hsize_t));
+                /* Copy ending point for this span */
+                **buf = curr->high;
                 (*buf)++;
 
                 /* Decrement the number of blocks processed */
@@ -2729,7 +4415,8 @@ done:
  REVISION LOG
 --------------------------------------------------------------------------*/
 static herr_t
-H5S__get_select_hyper_blocklist(H5S_t *space, hbool_t internal, hsize_t startblock, hsize_t numblocks, hsize_t *buf)
+H5S__get_select_hyper_blocklist(H5S_t *space, hsize_t startblock,
+    hsize_t numblocks, hsize_t *buf)
 {
     herr_t ret_value = SUCCEED; /* Return value */
 
@@ -2739,11 +4426,18 @@ H5S__get_select_hyper_blocklist(H5S_t *space, hbool_t internal, hsize_t startblo
     HDassert(buf);
     HDassert(space->select.sel_info.hslab->unlim_dim < 0);
 
+    /* Attempt to rebuild diminfo if it is invalid and has not been confirmed
+     * to be impossible.
+     */
+    if(space->select.sel_info.hslab->diminfo_valid == H5S_DIMINFO_VALID_NO)
+        H5S__hyper_rebuild(space);
+
     /* Check for a "regular" hyperslab selection */
     if(space->select.sel_info.hslab->diminfo_valid == H5S_DIMINFO_VALID_YES) {
         const H5S_hyper_dim_t *diminfo; /* Alias for dataspace's diminfo information */
         hsize_t tmp_count[H5S_MAX_RANK]; /* Temporary hyperslab counts */
         hsize_t offset[H5S_MAX_RANK];   /* Offset of element in dataspace */
+        hsize_t end[H5S_MAX_RANK];  /* End of elements in dataspace */
         unsigned fast_dim;          /* Rank of the fastest changing dimension for the dataspace */
         unsigned ndims;             /* Rank of the dataspace */
         hbool_t done;               /* Whether we are done with the iteration */
@@ -2754,31 +4448,25 @@ H5S__get_select_hyper_blocklist(H5S_t *space, hbool_t internal, hsize_t startblo
         fast_dim = ndims - 1;
 
         /* Check which set of dimension information to use */
-        if(internal)
+        if(space->select.sel_info.hslab->unlim_dim >= 0)
             /*
-             * Use the "optimized dimension information" to pass back information
-             * on the blocks set, not the "application information".
+             * There is an unlimited dimension so we must use diminfo.opt as
+             * it has been "clipped" to the current extent.
              */
             diminfo = space->select.sel_info.hslab->diminfo.opt;
         else
-            if(space->select.sel_info.hslab->unlim_dim >= 0)
-                /*
-                 * There is an unlimited dimension so we must use diminfo.opt as
-                 * it has been "clipped" to the current extent.
-                 */
-                diminfo = space->select.sel_info.hslab->diminfo.opt;
-            else
-                /*
-                 * Use the "application dimension information" to pass back to
-                 * the user the blocks they set, not the optimized, internal
-                 * information.
-                 */
-                diminfo = space->select.sel_info.hslab->diminfo.app;
+            /*
+             * Use the "application dimension information" to pass back to
+             * the user the blocks they set, not the optimized, internal
+             * information.
+             */
+            diminfo = space->select.sel_info.hslab->diminfo.app;
 
         /* Build the tables of count sizes as well as the initial offset */
         for(u = 0; u < ndims; u++) {
             tmp_count[u] = diminfo[u].count;
             offset[u] = diminfo[u].start;
+            end[u] = diminfo[u].start + (diminfo[u].block - 1);
         } /* end for */
 
         /* We're not done with the iteration */
@@ -2786,31 +4474,45 @@ H5S__get_select_hyper_blocklist(H5S_t *space, hbool_t internal, hsize_t startblo
 
         /* Go iterate over the hyperslabs */
         while(!done && numblocks > 0) {
-            hsize_t temp_off;           /* Offset in a given dimension */
+            /* Skip over initial blocks */
+            if(startblock > 0) {
+                /* Skip all blocks in row */
+                if(startblock >= tmp_count[fast_dim]) {
+                    startblock -= tmp_count[fast_dim];
+                    tmp_count[fast_dim] = 0;
+                } /* end if */
+                else {
+                    /* Move the offset to the next sequence to start */
+                    offset[fast_dim] += diminfo[fast_dim].stride * startblock;
+                    end[fast_dim] += diminfo[fast_dim].stride * startblock;
+
+                    /* Decrement the block count */
+                    tmp_count[fast_dim] -= startblock;
+
+                    /* Done with starting blocks */
+                    startblock = 0;
+                } /* end else */
+            } /* end if */
 
             /* Iterate over the blocks in the fastest dimension */
             while(tmp_count[fast_dim] > 0 && numblocks > 0) {
+                /* Sanity check */
+                HDassert(startblock == 0);
 
-                /* Check if we should copy this block information */
-                if(startblock == 0) {
-                    /* Copy the starting location */
-                    H5MM_memcpy(buf, offset, sizeof(hsize_t) * ndims);
-                    buf += ndims;
+                /* Copy the starting location */
+                H5MM_memcpy(buf, offset, sizeof(hsize_t) * ndims);
+                buf += ndims;
 
-                    /* Compute the ending location */
-                    H5MM_memcpy(buf, offset, sizeof(hsize_t) * ndims);
-                    for(u = 0; u < ndims; u++)
-                        buf[u] += (diminfo[u].block - 1);
-                    buf += ndims;
+                /* Compute the ending location */
+                H5MM_memcpy(buf, end, sizeof(hsize_t) * ndims);
+                buf += ndims;
 
-                    /* Decrement the number of blocks to retrieve */
-                    numblocks--;
-                } /* end if */
-                else
-                    startblock--;
+                /* Decrement the number of blocks to retrieve */
+                numblocks--;
 
                 /* Move the offset to the next sequence to start */
                 offset[fast_dim] += diminfo[fast_dim].stride;
+                end[fast_dim] += diminfo[fast_dim].stride;
 
                 /* Decrement the block count */
                 tmp_count[fast_dim]--;
@@ -2833,23 +4535,24 @@ H5S__get_select_hyper_blocklist(H5S_t *space, hbool_t internal, hsize_t startblo
                     if(tmp_count[temp_dim] > 0)
                         break;
 
+                    /* Reset the block count in this dimension */
+                    tmp_count[temp_dim] = diminfo[temp_dim].count;
+
                     /* Check for getting out of iterator */
                     if(temp_dim == 0)
                         done = TRUE;
 
-                    /* Reset the block count in this dimension */
-                    tmp_count[temp_dim] = diminfo[temp_dim].count;
-
                     /* Wrapped a dimension, go up to next dimension */
                     temp_dim--;
                 } /* end while */
             } /* end if */
 
-            /* Re-compute offset array */
-            for(u = 0; u < ndims; u++) {
-                temp_off = diminfo[u].start + diminfo[u].stride * (diminfo[u].count - tmp_count[u]);
-                offset[u] = temp_off;
-            } /* end for */
+            /* Re-compute offset & end arrays */
+            if(!done)
+                for(u = 0; u < ndims; u++) {
+                    offset[u] = diminfo[u].start + diminfo[u].stride * (diminfo[u].count - tmp_count[u]);
+                    end[u] = offset[u] + (diminfo[u].block - 1);
+                } /* end for */
         } /* end while */
     } /* end if */
     else {
@@ -2915,7 +4618,7 @@ H5Sget_select_hyper_blocklist(hid_t spaceid, hsize_t startblock,
 
     /* Go get the correct number of blocks */
     if(numblocks > 0)
-        ret_value = H5S__get_select_hyper_blocklist(space, 0, startblock, numblocks, buf);
+        ret_value = H5S__get_select_hyper_blocklist(space, startblock, numblocks, buf);
     else
         ret_value = SUCCEED;      /* Successfully got 0 blocks... */
 
@@ -2926,76 +4629,6 @@ done:
 
 /*--------------------------------------------------------------------------
  NAME
-    H5S_hyper_bounds_helper
- PURPOSE
-    Gets the bounding box containing the selection.
- USAGE
-    htri_t H5S_hyper_bounds_helper(spans, offset, rank);
-        const H5S_hyper_span_info_t *spans; IN: Pointer to current hyperslab span tree
-        const hssize_t *offset;         IN: Pointer to offset array
-        hsize_t rank;                   IN: Current rank looking at
-        hsize_t *start;                 OUT: Start array bounds
-        hsize_t *end;                   OUT: End array bounds
- RETURNS
-    Non-negative on success, negative on failure
- DESCRIPTION
-    Retrieves the bounding box containing the current selection and places
-    it into the user's buffers.  The start and end buffers must be large
-    enough to hold the dataspace rank number of coordinates.  The bounding box
-    exactly contains the selection, ie. if a 2-D element selection is currently
-    defined with the following points: (4,5), (6,8) (10,7), the bounding box
-    with be (4, 5), (10, 8).
-        The bounding box calculations _does_ include the current offset of the
-    selection within the dataspace extent.
- GLOBAL VARIABLES
- COMMENTS, BUGS, ASSUMPTIONS
- EXAMPLES
- REVISION LOG
---------------------------------------------------------------------------*/
-static herr_t
-H5S_hyper_bounds_helper(const H5S_hyper_span_info_t *spans, const hssize_t *offset, hsize_t rank, hsize_t *start, hsize_t *end)
-{
-    H5S_hyper_span_t *curr;             /* Hyperslab information nodes */
-    herr_t      ret_value = SUCCEED;    /* Return value */
-
-    FUNC_ENTER_NOAPI_NOINIT
-
-    HDassert(spans);
-    HDassert(offset);
-    HDassert(rank < H5S_MAX_RANK);
-    HDassert(start);
-    HDassert(end);
-
-    /* Check each point to determine whether selection+offset is within extent */
-    curr=spans->head;
-    while(curr!=NULL) {
-        /* Check for offset moving selection negative */
-        if(((hssize_t)curr->low + offset[rank]) < 0)
-            HGOTO_ERROR(H5E_DATASPACE, H5E_BADRANGE, FAIL, "offset moves selection out of bounds")
-
-        /* Check if the current span extends the bounding box */
-        if((curr->low + (hsize_t)offset[rank]) < start[rank])
-            start[rank] = curr->low + (hsize_t)offset[rank];
-        if((curr->high + (hsize_t)offset[rank]) > end[rank])
-            end[rank] = curr->high + (hsize_t)offset[rank];
-
-        /* Recurse if this node has down spans */
-        if(curr->down != NULL) {
-            if(H5S_hyper_bounds_helper(curr->down, offset, (rank + 1), start, end) < 0)
-                HGOTO_ERROR(H5E_DATASPACE, H5E_BADSELECT, FAIL, "failure in lower dimension")
-        } /* end if */
-
-        /* Advance to next node */
-        curr = curr->next;
-    } /* end while */
-
-done:
-    FUNC_LEAVE_NOAPI(ret_value)
-} /* end H5S_hyper_bounds_helper() */
-
-
-/*--------------------------------------------------------------------------
- NAME
     H5S__hyper_bounds
  PURPOSE
     Gets the bounding box containing the selection.
@@ -3023,8 +4656,7 @@ done:
 static herr_t
 H5S__hyper_bounds(const H5S_t *space, hsize_t *start, hsize_t *end)
 {
-    unsigned rank;              /* Dataspace rank */
-    unsigned i;                 /* index variable */
+    const hsize_t *low_bounds, *high_bounds;    /* Pointers to the correct pair of low & high bounds */
     herr_t ret_value = SUCCEED; /* Return value */
 
     FUNC_ENTER_STATIC
@@ -3034,37 +4666,42 @@ H5S__hyper_bounds(const H5S_t *space, hsize_t *start, hsize_t *end)
     HDassert(start);
     HDassert(end);
 
-    /* Set the start and end arrays up */
-    rank = space->extent.rank;
-    for(i = 0; i < rank; i++) {
-        start[i] = HSIZET_MAX;
-        end[i] = 0;
-    } /* end for */
-
-    /* Check for a "regular" hyperslab selection */
+    /* Check which set of low & high bounds we should be using */
     if(space->select.sel_info.hslab->diminfo_valid == H5S_DIMINFO_VALID_YES) {
-        const H5S_hyper_dim_t *diminfo = space->select.sel_info.hslab->diminfo.opt; /* local alias for diminfo */
+        low_bounds = space->select.sel_info.hslab->diminfo.low_bounds;
+        high_bounds = space->select.sel_info.hslab->diminfo.high_bounds;
+    } /* end if */
+    else {
+        low_bounds = space->select.sel_info.hslab->span_lst->low_bounds;
+        high_bounds = space->select.sel_info.hslab->span_lst->high_bounds;
+    } /* end else */
+
+    /* Check for offset set */
+    if(space->select.offset_changed) {
+        unsigned u;                 /* Local index variable */
+
+        /* Loop over dimensions */
+        for(u = 0; u < space->extent.rank; u++) {
+            /* Sanity check */
+            HDassert(low_bounds[u] <= high_bounds[u]);
 
-        /* Check each dimension */
-        for(i = 0; i < rank; i++) {
             /* Check for offset moving selection negative */
-            if((space->select.offset[i] + (hssize_t)diminfo[i].start) < 0)
+            if(((hssize_t)low_bounds[u] + space->select.offset[u]) < 0)
                 HGOTO_ERROR(H5E_DATASPACE, H5E_BADRANGE, FAIL, "offset moves selection out of bounds")
 
-            /* Compute the smallest location in this dimension */
-            start[i] = diminfo[i].start + (hsize_t)space->select.offset[i];
-
-            /* Compute the largest location in this dimension */
-            if((int)i == space->select.sel_info.hslab->unlim_dim)
-                end[i] = H5S_UNLIMITED;
+            /* Set the low & high bounds in this dimension */
+            start[u] = (hsize_t)((hssize_t)low_bounds[u] + space->select.offset[u]);
+            if((int)u == space->select.sel_info.hslab->unlim_dim)
+                end[u] = H5S_UNLIMITED;
             else
-                end[i] = diminfo[i].start + diminfo[i].stride * (diminfo[i].count - 1) + (diminfo[i].block - 1) + (hsize_t)space->select.offset[i];
+                end[u] = (hsize_t)((hssize_t)high_bounds[u] + space->select.offset[u]);
         } /* end for */
     } /* end if */
     else {
-        /* Call the recursive routine to get the bounds for the span tree */
-        ret_value = H5S_hyper_bounds_helper(space->select.sel_info.hslab->span_lst, space->select.offset, (hsize_t)0, start, end);
-    } /* end if */
+        /* Offset vector is still zeros, just copy low & high bounds */
+        H5MM_memcpy(start, low_bounds, sizeof(hsize_t) * space->extent.rank);
+        H5MM_memcpy(end, high_bounds, sizeof(hsize_t) * space->extent.rank);
+    } /* end else */
 
 done:
     FUNC_LEAVE_NOAPI(ret_value)
@@ -3115,6 +4752,7 @@ H5S__hyper_offset(const H5S_t *space, hsize_t *offset)
     dim_size = space->extent.size;
 
     /* Check for a "regular" hyperslab selection */
+    /* (No need to rebuild the dimension info yet -QAK) */
     if(space->select.sel_info.hslab->diminfo_valid == H5S_DIMINFO_VALID_YES) {
         const H5S_hyper_dim_t *diminfo = space->select.sel_info.hslab->diminfo.opt; /* Local alias for diminfo */
 
@@ -3279,6 +4917,7 @@ H5S__hyper_is_contiguous(const H5S_t *space)
     HDassert(space);
 
     /* Check for a "regular" hyperslab selection */
+    /* (No need to rebuild the dimension info yet -QAK) */
     if(space->select.sel_info.hslab->diminfo_valid == H5S_DIMINFO_VALID_YES) {
         const H5S_hyper_dim_t *diminfo=space->select.sel_info.hslab->diminfo.opt; /* local alias for diminfo */
 
@@ -3297,7 +4936,7 @@ H5S__hyper_is_contiguous(const H5S_t *space)
 
         /* Initialize flags */
         large_contiguous = TRUE;    /* assume true and reset if the dimensions don't match */
-        small_contiguous = FALSE;   /* assume false initially */
+        small_contiguous = FALSE;    /* assume false initially */
 
         /* Check for a "large contigous" block */
         for(u = 0; u < space->extent.rank; u++) {
@@ -3343,7 +4982,7 @@ H5S__hyper_is_contiguous(const H5S_t *space)
          */
         /* Initialize flags */
         large_contiguous = TRUE;    /* assume true and reset if the dimensions don't match */
-        small_contiguous = FALSE;   /* assume false initially */
+        small_contiguous = FALSE;    /* assume false initially */
 
         /* Get information for slowest changing information */
         spans = space->select.sel_info.hslab->span_lst;
@@ -3461,6 +5100,9 @@ H5S__hyper_is_single(const H5S_t *space)
     HDassert(space);
 
     /* Check for a "single" hyperslab selection */
+    /* (No need to rebuild the dimension info yet, since the span-tree
+     *  algorithm is fast -QAK)
+     */
     if(space->select.sel_info.hslab->diminfo_valid == H5S_DIMINFO_VALID_YES) {
         unsigned u;                     /* index variable */
 
@@ -3519,7 +5161,6 @@ done:
     This is primarily used for reading the entire selection in one swoop.
  GLOBAL VARIABLES
  COMMENTS, BUGS, ASSUMPTIONS
-    Doesn't check for "regular" hyperslab selections composed of spans
  EXAMPLES
  REVISION LOG
 --------------------------------------------------------------------------*/
@@ -3533,6 +5174,12 @@ H5S__hyper_is_regular(const H5S_t *space)
     /* Check args */
     HDassert(space);
 
+    /* Attempt to rebuild diminfo if it is invalid and has not been confirmed
+     * to be impossible.
+     */
+    if(space->select.sel_info.hslab->diminfo_valid == H5S_DIMINFO_VALID_NO)
+        H5S__hyper_rebuild((H5S_t *)space);     /* Casting away const OK -NAF */
+
     /* Only simple check for regular hyperslabs for now... */
     if(space->select.sel_info.hslab->diminfo_valid == H5S_DIMINFO_VALID_YES)
         ret_value = TRUE;
@@ -3545,88 +5192,395 @@ H5S__hyper_is_regular(const H5S_t *space)
 
 /*--------------------------------------------------------------------------
  NAME
-    H5S__hyper_release
+    H5S__hyper_spans_shape_same_helper
  PURPOSE
-    Release hyperslab selection information for a dataspace
+    Helper routine to check if two hyperslab span trees are the same shape
  USAGE
-    herr_t H5S__hyper_release(space)
-        H5S_t *space;       IN: Pointer to dataspace
+    hbool_t H5S__hyper_spans_shape_same_helper(span1, span2, offset, rest_zeros)
+        H5S_hyper_span_info_t *span_info1;      IN: First span tree to compare
+        H5S_hyper_span_info_t *span_info2;      IN: Second span tree to compare
+        hssize_t offset[];                      IN: Offset between the span trees
+        hbool_t rest_zeros[];                   IN: Array of flags which indicate
+                                                    the rest of the offset[] array
+                                                    is zero values.
  RETURNS
-    Non-negative on success/Negative on failure
+    TRUE (1) or FALSE (0) on success, can't fail
  DESCRIPTION
-    Releases all hyperslab selection information for a dataspace
+    Compare two hyperslab span trees to determine if they refer to a selection
+    with the same shape, with a possible (constant) offset between their
+    elements.  Very similar to H5S__hyper_cmp_spans, except the selected
+    elements can be offset by a vector.
  GLOBAL VARIABLES
  COMMENTS, BUGS, ASSUMPTIONS
  EXAMPLES
  REVISION LOG
 --------------------------------------------------------------------------*/
-static herr_t
-H5S__hyper_release(H5S_t *space)
+static H5_ATTR_PURE hbool_t
+H5S__hyper_spans_shape_same_helper(const H5S_hyper_span_info_t *span_info1,
+    const H5S_hyper_span_info_t *span_info2, hssize_t offset[],
+    hbool_t rest_zeros[])
 {
-    herr_t ret_value = SUCCEED;
+    hbool_t ret_value = TRUE;   /* Return value */
+
+    FUNC_ENTER_PACKAGE_NOERR
+
+    /* Sanity checks */
+    HDassert(span_info1);
+    HDassert(span_info2);
+    HDassert(offset);
+    HDassert(rest_zeros);
+
+    /* Compare low & high bounds for this span list */
+    /* (Could compare lower dimensions also, but not certain if
+     *      that's worth it. - QAK, 2019/01/23)
+     */
+    if((hsize_t)((hssize_t)span_info1->low_bounds[0] + offset[0]) != span_info2->low_bounds[0])
+        HGOTO_DONE(FALSE)
+    else if((hsize_t)((hssize_t)span_info1->high_bounds[0] + offset[0]) != span_info2->high_bounds[0])
+        HGOTO_DONE(FALSE)
+    else {
+        const H5S_hyper_span_t *span1;
+        const H5S_hyper_span_t *span2;
+
+        /* Get the pointers to the actual lists of spans */
+        span1 = span_info1->head;
+        span2 = span_info2->head;
+
+        /* Sanity checking */
+        HDassert(span1);
+        HDassert(span2);
+
+        /* infinite loop which must be broken out of */
+        while(1) {
+            /* Check for both spans being NULL */
+            if(span1 == NULL && span2 == NULL)
+                HGOTO_DONE(TRUE)
+
+            /* Check for one span being NULL */
+            if(span1 == NULL || span2 == NULL)
+                HGOTO_DONE(FALSE)
+
+            /* Check if the actual low & high span information is the same */
+            if((hsize_t)((hssize_t)span1->low + offset[0]) != span2->low || (hsize_t)((hssize_t)span1->high + offset[0]) != span2->high)
+                HGOTO_DONE(FALSE)
+
+            /* Check for down tree for this span */
+            if(span1->down != NULL || span2->down != NULL) {
+                /* If the rest of the span trees have a zero offset, use the faster comparison routine */
+                if(rest_zeros[0]) {
+                    if(!H5S__hyper_cmp_spans(span1->down, span2->down))
+                        HGOTO_DONE(FALSE)
+                    else {
+                        /* Keep going... */
+                    } /* end else */
+                } /* end if */
+                else {
+                    if(!H5S__hyper_spans_shape_same_helper(span1->down, span2->down, &offset[1], &rest_zeros[1]))
+                        HGOTO_DONE(FALSE)
+                    else {
+                        /* Keep going... */
+                    } /* end else */
+                } /* end else */
+            } /* end if */
+            else {
+                /* Keep going... */
+            } /* end else */
+
+            /* Advance to the next nodes in the span list */
+            span1 = span1->next;
+            span2 = span2->next;
+        } /* end while */
+    } /* end else */
+
+    /* Fall through, with default return value of 'TRUE' if spans were already visited */
+
+done:
+    FUNC_LEAVE_NOAPI(ret_value)
+} /* end H5S__hyper_spans_shape_same_helper() */
+
+
+/*--------------------------------------------------------------------------
+ NAME
+    H5S__hyper_spans_shape_same
+ PURPOSE
+    Check if two hyperslab span trees are the same shape
+ USAGE
+    hbool_t H5S__hyper_spans_shape_same(span1, span2)
+        H5S_hyper_span_info_t *span_info1;      IN: First span tree to compare
+        H5S_hyper_span_info_t *span_info2;      IN: Second span tree to compare
+ RETURNS
+    TRUE (1) or FALSE (0) on success, can't fail
+ DESCRIPTION
+    Compare two hyperslab span trees to determine if they refer to a selection
+    with the same shape.  Very similar to H5S__hyper_cmp_spans, except the
+    selected elements can be offset by a vector.
+ GLOBAL VARIABLES
+ COMMENTS, BUGS, ASSUMPTIONS
+ EXAMPLES
+ REVISION LOG
+--------------------------------------------------------------------------*/
+static H5_ATTR_PURE hbool_t
+H5S__hyper_spans_shape_same(const H5S_hyper_span_info_t *span_info1,
+    const H5S_hyper_span_info_t *span_info2, unsigned ndims)
+{
+    const H5S_hyper_span_t *span1;  /* Pointer to spans in first span tree */
+    const H5S_hyper_span_t *span2;  /* Pointer to spans in second span tree */
+    hssize_t offset[H5S_MAX_RANK];  /* Offset vector for selections */
+    hbool_t rest_zeros[H5S_MAX_RANK]; /* Vector of flags to indicate when remaining offset is all zero */
+    hbool_t zero_offset;            /* Whether the two selections have a non-zero offset */
+    unsigned u;                     /* Local index variable */
+    hbool_t ret_value = TRUE;       /* Return value */
+
+    FUNC_ENTER_STATIC_NOERR
+
+    /* Sanity check */
+    HDassert(span_info1);
+    HDassert(span_info2);
+    HDassert(ndims > 0);
+
+    /* Initialize arrays */
+    HDmemset(offset, 0, sizeof(offset));
+    HDmemset(rest_zeros, 0, sizeof(rest_zeros));
+
+    /* Check for an offset between the two selections */
+    span1 = span_info1->head;
+    span2 = span_info2->head;
+    zero_offset = TRUE;
+    for(u = 0; u < ndims; u++) {
+        /* Check for offset in this dimension */
+        if(span1->low != span2->low) {
+            offset[u] = (hssize_t)span2->low - (hssize_t)span1->low;
+
+            /* Indicate that the offset vector is not all zeros */
+            if(zero_offset)
+                zero_offset = FALSE;
+        } /* end if */
+
+        /* Sanity check */
+        /* (Both span trees must have the same depth) */
+        HDassert((span1->down && span2->down) || (NULL == span1->down && NULL == span2->down));
+
+        /* Advance to next dimension */
+        if(span1->down) {
+            span1 = span1->down->head;
+            span2 = span2->down->head;
+        } /* end if */
+    } /* end for */
+
+    /* Check if there's a "tail" of all zeros in a non-zero offset vector */
+    if(!zero_offset) {
+        int i;          /* Local index variable */
+
+        /* Find first non-zero offset, from the fastest dimension up */
+        for(i = (int)(ndims - 1); i >= 0; i--)
+            if(offset[i]) {
+                rest_zeros[i] = TRUE;
+                break;
+            } /* end if */
+
+        /* Sanity check */
+        /* (Must eventually have found a non-zero offset) */
+        HDassert(i >= 0);
+    } /* end if */
+
+    /* If the offset vector is all zero, we can use the faster span tree
+     *  comparison routine.  Otherwise, use a generalized version of that
+     *  routine.
+     */
+    if(zero_offset)
+        ret_value = H5S__hyper_cmp_spans(span_info1, span_info2);
+    else
+        ret_value = H5S__hyper_spans_shape_same_helper(span_info1, span_info2, offset, rest_zeros);
+
+    FUNC_LEAVE_NOAPI(ret_value)
+} /* end H5S__hyper_spans_shape_same() */
+
+
+/*--------------------------------------------------------------------------
+ NAME
+    H5S__hyper_shape_same
+ PURPOSE
+    Check if a two hyperslab selections are the same shape
+ USAGE
+    htri_t H5S__hyper_shape_same(space1, space2)
+        const H5S_t *space1;     IN: First dataspace to check
+        const H5S_t *space2;     IN: Second dataspace to check
+ RETURNS
+    TRUE / FALSE / FAIL
+ DESCRIPTION
+    Checks to see if the current selection in each dataspace are the same
+    shape.
+ GLOBAL VARIABLES
+ COMMENTS, BUGS, ASSUMPTIONS
+    Handles when both are regular in an efficient way, otherwise converts
+    both to span tree form (if necessary) and compares efficiently them in
+    that form.
+
+    Rank of space1 must always be >= to rank of space2.
+ EXAMPLES
+ REVISION LOG
+--------------------------------------------------------------------------*/
+static htri_t
+H5S__hyper_shape_same(const H5S_t *space1, const H5S_t *space2)
+{
+    unsigned space1_rank;       /* Number of dimensions of first dataspace */
+    unsigned space2_rank;       /* Number of dimensions of second dataspace */
+    htri_t ret_value = TRUE;    /* Return value */
 
     FUNC_ENTER_STATIC
 
     /* Check args */
-    HDassert(space && H5S_SEL_HYPERSLABS == H5S_GET_SELECT_TYPE(space));
+    HDassert(space1);
+    HDassert(space2);
 
-    /* Reset the number of points selected */
-    space->select.num_elem = 0;
+    /* Get dataspace ranks */
+    space1_rank = space1->extent.rank;
+    space2_rank = space2->extent.rank;
 
-    /* Release irregular hyperslab information */
-    if(space->select.sel_info.hslab) {
-        if(space->select.sel_info.hslab->span_lst != NULL)
-            if(H5S__hyper_free_span_info(space->select.sel_info.hslab->span_lst) < 0)
-                HGOTO_ERROR(H5E_INTERNAL, H5E_CANTFREE, FAIL, "failed to release hyperslab spans")
+    /* Sanity check */
+    HDassert(space1_rank >= space2_rank);
+    HDassert(space2_rank > 0);
+
+    /* Rebuild diminfo if it is invalid and has not been confirmed to be
+     * impossible */
+    if(space1->select.sel_info.hslab->diminfo_valid == H5S_DIMINFO_VALID_NO)
+        H5S__hyper_rebuild((H5S_t *)space1);    /* Casting away const OK -QAK */
+    if(space2->select.sel_info.hslab->diminfo_valid == H5S_DIMINFO_VALID_NO)
+        H5S__hyper_rebuild((H5S_t *)space2);    /* Casting away const OK -QAK */
+
+    /* If both are regular hyperslabs, compare their diminfo values */
+    if(space1->select.sel_info.hslab->diminfo_valid == H5S_DIMINFO_VALID_YES
+            && space2->select.sel_info.hslab->diminfo_valid == H5S_DIMINFO_VALID_YES) {
+        int space1_dim;         /* Current dimension in first dataspace */
+        int space2_dim;         /* Current dimension in second dataspace */
+
+        /* Initialize dimensions */
+        space1_dim = (int)space1_rank - 1;
+        space2_dim = (int)space2_rank - 1;
+
+        /* Check that the shapes are the same in the common dimensions, and that
+         * block == 1 in all dimensions that appear only in space1.
+         */
+        while(space2_dim >= 0) {
+            if(space1->select.sel_info.hslab->diminfo.opt[space1_dim].stride !=
+                    space2->select.sel_info.hslab->diminfo.opt[space2_dim].stride)
+                HGOTO_DONE(FALSE)
 
-        /* Release space for the hyperslab selection information */
-        space->select.sel_info.hslab = H5FL_FREE(H5S_hyper_sel_t, space->select.sel_info.hslab);
+            if(space1->select.sel_info.hslab->diminfo.opt[space1_dim].count !=
+                    space2->select.sel_info.hslab->diminfo.opt[space2_dim].count)
+                HGOTO_DONE(FALSE)
+
+            if(space1->select.sel_info.hslab->diminfo.opt[space1_dim].block !=
+                    space2->select.sel_info.hslab->diminfo.opt[space2_dim].block)
+                HGOTO_DONE(FALSE)
+
+            space1_dim--;
+            space2_dim--;
+        } /* end while */
+
+        while(space1_dim >= 0) {
+            if(space1->select.sel_info.hslab->diminfo.opt[space1_dim].block != 1)
+                HGOTO_DONE(FALSE)
+
+            space1_dim--;
+        } /* end while */
     } /* end if */
+    /* If both aren't regular, use fast irregular comparison */
+    else {
+        H5S_hyper_span_info_t *spans1;     /* Hyperslab spans for first dataspace */
+
+        /* Make certain that both selections have span trees */
+        if(NULL == space1->select.sel_info.hslab->span_lst)
+            if(H5S__hyper_generate_spans((H5S_t *)space1) < 0)  /* Casting away const OK -QAK */
+                HGOTO_ERROR(H5E_DATASPACE, H5E_UNINITIALIZED, FAIL, "can't construct span tree for hyperslab selection")
+        if(NULL == space2->select.sel_info.hslab->span_lst)
+            if(H5S__hyper_generate_spans((H5S_t *)space2) < 0)  /* Casting away const OK -QAK */
+                HGOTO_ERROR(H5E_DATASPACE, H5E_UNINITIALIZED, FAIL, "can't construct span tree for hyperslab selection")
+
+        /* If rank of space A is different (guaranteed greater) than
+         *      rank of space B, walk down the span tree, verifying
+         *      that the block size is 1 on the way down.
+         */
+        if(space1_rank > space2_rank) {
+            unsigned diff_rank = space1_rank - space2_rank;   /* Difference in ranks */
+
+            /* Walk down the dimensions */
+            spans1 = space1->select.sel_info.hslab->span_lst;
+            while(diff_rank > 0) {
+                H5S_hyper_span_t *span;         /* Span for this dimension */
+
+                /* Get pointer to first span in tree */
+                span = spans1->head;
+
+                /* Check for more spans in this dimension */
+                if(span->next)
+                    HGOTO_DONE(FALSE)
+
+                /* Check for span size > 1 element */
+                if(span->low != span->high)
+                    HGOTO_DONE(FALSE)
+
+                /* Walk down to the next dimension */
+                spans1 = span->down;
+                diff_rank--;
+            } /* end while */
+
+            /* Sanity check */
+            HDassert(spans1);
+        } /* end if */
+        else
+            spans1 = space1->select.sel_info.hslab->span_lst;
+
+        /* Compare the span trees */
+        ret_value = H5S__hyper_spans_shape_same(spans1, space2->select.sel_info.hslab->span_lst, space2_rank);
+    } /* end else */
+
+    /* Fall through with 'TRUE' value, if not set earlier */
 
 done:
     FUNC_LEAVE_NOAPI(ret_value)
-} /* end H5S__hyper_release() */
+} /* end H5S__hyper_shape_same() */
 
 
 /*--------------------------------------------------------------------------
  NAME
-    H5S__hyper_recover_span
+    H5S__hyper_release
  PURPOSE
-    Recover a generated span, if appropriate
+    Release hyperslab selection information for a dataspace
  USAGE
-    herr_t H5S__hyper_recover_span(recover, curr_span, next_span)
-        unsigned *recover;                 IN/OUT: Pointer recover flag
-        H5S_hyper_span_t **curr_span;   IN/OUT: Pointer to current span in list
-        H5S_hyper_span_t *next_span;    IN: Pointer to next span
+    herr_t H5S__hyper_release(space)
+        H5S_t *space;       IN: Pointer to dataspace
  RETURNS
-    Non-negative on success, negative on failure
+    Non-negative on success/Negative on failure
  DESCRIPTION
-    Check if the current span needs to be recovered and free it if so.
-    Set the current span to the next span in any case.
+    Releases all hyperslab selection information for a dataspace
  GLOBAL VARIABLES
  COMMENTS, BUGS, ASSUMPTIONS
  EXAMPLES
  REVISION LOG
 --------------------------------------------------------------------------*/
 static herr_t
-H5S__hyper_recover_span(hbool_t *recover, H5S_hyper_span_t **curr_span, H5S_hyper_span_t *next_span)
+H5S__hyper_release(H5S_t *space)
 {
     FUNC_ENTER_STATIC_NOERR
 
-    HDassert(recover);
-    HDassert(curr_span);
+    /* Check args */
+    HDassert(space && H5S_SEL_HYPERSLABS == H5S_GET_SELECT_TYPE(space));
 
-    /* Check if the span should be recovered */
-    if(*recover) {
-        H5S__hyper_free_span(*curr_span);
-        *recover = FALSE;
-    } /* end if */
+    /* Reset the number of points selected */
+    space->select.num_elem = 0;
+
+    /* Release irregular hyperslab information */
+    if(space->select.sel_info.hslab) {
+        if(space->select.sel_info.hslab->span_lst != NULL)
+            H5S__hyper_free_span_info(space->select.sel_info.hslab->span_lst);
 
-    /* Set the current span to next span */
-    *curr_span = next_span;
+        /* Release space for the hyperslab selection information */
+        space->select.sel_info.hslab = H5FL_FREE(H5S_hyper_sel_t, space->select.sel_info.hslab);
+    } /* end if */
 
     FUNC_LEAVE_NOAPI(SUCCEED)
-} /* end H5S__hyper_recover_span() */
+} /* end H5S__hyper_release() */
 
 
 /*--------------------------------------------------------------------------
@@ -3639,7 +5593,7 @@ H5S__hyper_recover_span(hbool_t *recover, H5S_hyper_span_t **curr_span, H5S_hype
         unsigned rank;                  IN: Number of dimensions of coordinate
         hsize_t *coords;               IN: Location of element
  RETURNS
-    Non-negative on success, negative on failure
+    Non-NULL pointer to new span tree on success, NULL on failure
  DESCRIPTION
     Create a span tree for a single element
  GLOBAL VARIABLES
@@ -3661,14 +5615,20 @@ H5S__hyper_coord_to_span(unsigned rank, const hsize_t *coords)
 
     /* Search for location to insert new element in tree */
     if(rank > 1) {
-        /* Allocate a span info node */
-        if(NULL == (down = H5FL_CALLOC(H5S_hyper_span_info_t)))
+        /* Allocate a span info node for coordinates below this one */
+        if(NULL == (down = H5S__hyper_new_span_info(rank - 1)))
             HGOTO_ERROR(H5E_DATASPACE, H5E_CANTALLOC, NULL, "can't allocate hyperslab span")
 
+        /* Set the low & high bounds for this span info node */
+        H5MM_memcpy(down->low_bounds, &coords[1], (rank - 1) * sizeof(hsize_t));
+        H5MM_memcpy(down->high_bounds, &coords[1], (rank - 1) * sizeof(hsize_t));
 
         /* Build span tree for coordinates below this one */
         if(NULL == (down->head = H5S__hyper_coord_to_span(rank - 1, &coords[1])))
             HGOTO_ERROR(H5E_DATASPACE, H5E_CANTALLOC, NULL, "can't allocate hyperslab span")
+
+       /* Update the tail pointer of the down dimension, and it's a single span element */
+       down->tail = down->head;
     } /* end if */
 
     /* Build span for this coordinate */
@@ -3690,12 +5650,13 @@ done:
  NAME
     H5S__hyper_add_span_element_helper
  PURPOSE
-    Add a single element to a span tree
+    Helper routine to add a single element to a span tree
  USAGE
-    herr_t H5S_hyper_add_span_element_helper(prev_span, span_tree, rank, coords)
+    herr_t H5S__hyper_add_span_element_helper(span_tree, rank, coords, first_dim_modified)
         H5S_hyper_span_info_t *span_tree;  IN/OUT: Pointer to span tree to append to
         unsigned rank;                  IN: Number of dimensions of coordinates
-        hsize_t *coords;               IN: Location of element to add to span tree
+        hsize_t *coords;                IN: Location of element to add to span tree
+        int *first_dim_modified;        IN: Index of the first dimension modified
  RETURNS
     Non-negative on success, negative on failure
  DESCRIPTION
@@ -3708,13 +5669,9 @@ done:
 --------------------------------------------------------------------------*/
 static herr_t
 H5S__hyper_add_span_element_helper(H5S_hyper_span_info_t *span_tree,
-    unsigned rank, const hsize_t *coords)
+    unsigned rank, const hsize_t *coords, int *first_dim_modified)
 {
-    H5S_hyper_span_info_t *tspan_info;  /* Temporary pointer to span info */
-    H5S_hyper_span_info_t *prev_span_info;  /* Pointer to span info for level above current position */
-    H5S_hyper_span_t *tmp_span;         /* Temporary pointer to a span */
-    H5S_hyper_span_t *tmp2_span;        /* Another temporary pointer to a span */
-    H5S_hyper_span_t *new_span;         /* New span created for element */
+    H5S_hyper_span_t *tail_span;        /* Pointer to the tail span of one dimension */
     herr_t ret_value = SUCCEED;         /* Return value */
 
     FUNC_ENTER_STATIC
@@ -3723,166 +5680,196 @@ H5S__hyper_add_span_element_helper(H5S_hyper_span_info_t *span_tree,
     HDassert(span_tree);
     HDassert(rank > 0);
     HDassert(coords);
+    HDassert(first_dim_modified);
 
     /* Get pointer to last span in span tree */
-    tspan_info=span_tree;
-    if(span_tree->scratch)
-        tmp_span=(H5S_hyper_span_t *)span_tree->scratch;
-    else {
-        tmp_span=span_tree->head;
-        HDassert(tmp_span);
-        span_tree->scratch=(H5S_hyper_span_info_t *)tmp_span;
-    } /* end else */
-
-    /* Find last span tree which includes a portion of the coordinate */
-    prev_span_info=NULL;
-    while(coords[0]>=tmp_span->low && coords[0]<=tmp_span->high) {
-        /* Move rank & coordinate offset down a dimension */
-        rank--;
-        coords++;
-
-        /* Remember the span tree we are descending into */
-        prev_span_info=tspan_info;
-        tspan_info=tmp_span->down;
+    tail_span = span_tree->tail;
+
+    /* Determine if tail span includes a portion of the coordinate */
+    /* (Should never happen with the lowest level in the span tree) */
+    if(coords[0] >= tail_span->low && coords[0] <= tail_span->high) {
+        H5S_hyper_span_t *prev_down_tail_span;  /* Pointer to previous down spans' tail pointer */
+        hsize_t prev_down_tail_span_high;       /* Value of previous down spans' tail's high value */
+
+        /* Retain into about down spans' tail */
+        prev_down_tail_span = tail_span->down->tail;
+        prev_down_tail_span_high = tail_span->down->tail->high;
+
+        /* Drop down a dimension */
+        HDassert(rank > 1);
+        if(H5S__hyper_add_span_element_helper(tail_span->down, rank - 1, &coords[1], first_dim_modified) < 0)
+            HGOTO_ERROR(H5E_DATASET, H5E_CANTINSERT, FAIL, "can't insert coordinate into span tree")
+
+        /* Check & update high bounds for lower dimensions */
+        if(*first_dim_modified >= 0) {
+            unsigned first_dim; /* First dimension modified, relative to this span tree */
+            hbool_t first_dim_set = FALSE;      /* Whether first dimension modified is set */
+            unsigned u;         /* Local index variable */
 
-        /* Get the last span in this span's 'down' tree */
-        if(tspan_info->scratch)
-            tmp_span=(H5S_hyper_span_t *)tspan_info->scratch;
-        else {
-            tmp_span=tspan_info->head;
-            HDassert(tmp_span);
-            tspan_info->scratch=(H5S_hyper_span_info_t *)tmp_span;
-        } /* end else */
-    } /* end while */
+            /* Adjust first dimension modified to be relative to this span tree */
+            first_dim = (unsigned)(*first_dim_modified + 1);
 
-    /* Check if we made it all the way to the bottom span in the tree */
-    if(rank>1) {
-        /* Before we create another span at this level in the tree, check if
-         * the last span's "down tree" was equal to any other spans in this
-         * list of spans in the span tree.
-         *
-         * If so, release last span information and make last span merge into
-         * previous span (if possible), or at least share their "down tree"
-         * information.
-         */
-        tmp2_span=tspan_info->head;
-        while(tmp2_span!=tmp_span) {
-            if(H5S__hyper_cmp_spans(tmp2_span->down,tmp_span->down)==TRUE) {
-                /* Check for merging into previous span */
-                if(tmp2_span->high+1==tmp_span->low) {
-                    /* Release last span created */
-                    H5S__hyper_free_span(tmp_span);
+            /* Reset modified dimension, in case no bounds in this span tree change */
+            *first_dim_modified = -1;
 
-                    /* Increase size of previous span */
-                    tmp2_span->high++;
-                    tmp2_span->nelem++;
+            /* Iterate through coordinates */
+            for(u = first_dim; u < rank; u++) {
+                /* Check if coordinate is outside the bounds for this span tree */
+                if(coords[u] > span_tree->high_bounds[u]) {
+                    /* Update high bounds for this tree */
+                    span_tree->high_bounds[u] = coords[u];
 
-                    /* Reset the 'tmp_span' for the rest of this block's algorithm */
-                    tmp_span=tmp2_span;
+                    /* Need to signal to higher dimensions if high bounds changed */
+                    if(!first_dim_set) {
+                        *first_dim_modified = (int)u;
+                        first_dim_set = TRUE;
+                    } /* end if */
                 } /* end if */
-                /* Span is disjoint, but has the same "down tree" selection */
-                else {
-                    /* Release "down tree" information */
-                    H5S__hyper_free_span_info(tmp_span->down);
+            } /* end for */
+        } /* end if */
 
-                    /* Point at earlier span's "down tree" */
-                    tmp_span->down=tmp2_span->down;
+        /* Check if previous tail span in down spans is different than current
+         * tail span, or if its high value changed, in which case we should
+         * check if the updated node can share down spans with other nodes.
+         */
+        if(tail_span->down->tail != prev_down_tail_span ||
+                prev_down_tail_span_high != tail_span->down->tail->high) {
+            H5S_hyper_span_t *stop_span; /* Pointer to span to stop at */
+            H5S_hyper_span_t *tmp_span; /* Temporary pointer to a span */
+            uint64_t op_gen;            /* Operation generation value */
+
+            /* Determine which span to stop at */
+            if(tail_span->down->tail != prev_down_tail_span) {
+                /* Sanity check */
+                HDassert(prev_down_tail_span->next == tail_span->down->tail);
+
+                /* Set the span to stop at */
+                stop_span = prev_down_tail_span;
+            } /* end if */
+            else {
+                /* Sanity check */
+                HDassert(prev_down_tail_span_high != tail_span->down->tail->high);
 
-                    /* Increment reference count on shared "down tree" */
-                    tmp_span->down->count++;
-                } /* end else */
+                /* Set the span to stop at */
+                stop_span = tail_span->down->tail;
+            } /* end else */
 
-                /* Found span to merge into, break out now */
-                break;
-            } /* end if */
+            /* Acquire an operation generation value for this operation */
+            op_gen = H5S__hyper_get_op_gen();
 
-            /* Advance to next span to check */
-            tmp2_span=tmp2_span->next;
-        } /* end while */
+            /* Check if the 'stop' span in the "down tree" is equal to any other
+             * spans in the list of spans in the span tree.
+             *
+             * If so, release last span information and make last span merge into
+             * previous span (if possible), or at least share their "down tree"
+             * information.
+             */
+            tmp_span = tail_span->down->head;
+            while(tmp_span != stop_span) {
+                hbool_t attempt_merge_spans = FALSE;    /* Whether to merge spans */
 
-        /* Make span tree for current coordinates */
-        if(NULL == (new_span = H5S__hyper_coord_to_span(rank, coords)))
-            HGOTO_ERROR(H5E_RESOURCE, H5E_NOSPACE, FAIL, "can't allocate hyperslab span")
+                /* Different tests for when to run the 'merge' algorithm,
+                 * depending whether there's "down trees" or not.
+                 */
+                if(NULL == tmp_span->down) {
+                    /* Spin through spans until we find the one before the 'stop' span */
+                    if(tmp_span->next == stop_span)
+                        attempt_merge_spans = TRUE;
+                } /* end if */
+                else {
+                    /* Check if we've compared the 'stop' span's "down tree" to
+                     *      this span's "down tree" already.
+                     */
+                    if(tmp_span->down->op_info[0].op_gen != op_gen) {
+                        if(H5S__hyper_cmp_spans(tmp_span->down, stop_span->down))
+                            attempt_merge_spans = TRUE;
+
+                        /* Remember that we visited this span's "down tree" already */
+                        /* (Because it wasn't the same as the 'stop' span's down tree
+                         *      and we don't need to compare it again)
+                         */
+                        tmp_span->down->op_info[0].op_gen = op_gen;
+                    } /* end if */
+                } /* end else */
 
-        /* Add new span tree as span */
-        HDassert(tmp_span);
-        tmp_span->next=new_span;
+                /* Check for merging into previous span */
+                if(attempt_merge_spans) {
+                    if(tmp_span->high + 1 == stop_span->low) {
+                        /* Increase size of previous span */
+                        tmp_span->high++;
 
-        /* Make scratch pointer point to last span in list */
-        HDassert(tspan_info);
-        tspan_info->scratch=(H5S_hyper_span_info_t *)new_span;
+                        /* Update pointers appropriately */
+                        if(stop_span == prev_down_tail_span) {
+                            /* Sanity check */
+                            HDassert(stop_span->next == tail_span->down->tail);
 
-        /* Set the proper 'pstride' for new span */
-        new_span->pstride=new_span->low-tmp_span->low;
-    } /* end if */
-    else {
-        /* Does new node adjoin existing node? */
-        if(tmp_span->high+1==coords[0]) {
-            tmp_span->high++;
-            tmp_span->nelem++;
-
-            /* Check if this span tree should now be merged with a level higher in the tree */
-            if(prev_span_info!=NULL) {
-                /* Before we create another span at this level in the tree, check if
-                 * the last span's "down tree" was equal to any other spans in this
-                 * list of spans in the span tree.
-                 *
-                 * If so, release last span information and make last span merge into
-                 * previous span (if possible), or at least share their "down tree"
-                 * information.
-                 */
-                tmp2_span=prev_span_info->head;
-                tmp_span=(H5S_hyper_span_t *)prev_span_info->scratch;
-                while(tmp2_span!=tmp_span) {
-                    if(H5S__hyper_cmp_spans(tmp2_span->down,tmp_span->down)==TRUE) {
-                        /* Check for merging into previous span */
-                        if(tmp2_span->high+1==tmp_span->low) {
-                            /* Release last span created */
-                            H5S__hyper_free_span(tmp_span);
-
-                            /* Increase size of previous span */
-                            tmp2_span->high++;
-                            tmp2_span->nelem++;
-
-                            /* Update pointers */
-                            tmp2_span->next=NULL;
-                            prev_span_info->scratch=(H5S_hyper_span_info_t *)tmp2_span;
+                            tmp_span->next = stop_span->next;
                         } /* end if */
-                        /* Span is disjoint, but has the same "down tree" selection */
                         else {
-                            /* Release "down tree" information */
-                            H5S__hyper_free_span_info(tmp_span->down);
+                            /* Sanity check */
+                            HDassert(tmp_span->next == tail_span->down->tail);
 
-                            /* Point at earlier span's "down tree" */
-                            tmp_span->down=tmp2_span->down;
-
-                            /* Increment reference count on shared "down tree" */
-                            tmp_span->down->count++;
+                            tmp_span->next = NULL;
+                            tail_span->down->tail = tmp_span;
                         } /* end else */
 
-                        /* Found span to merge into, break out now */
-                        break;
+                        /* Release last span created */
+                        H5S__hyper_free_span(stop_span);
                     } /* end if */
+                    /* Span is disjoint, but has the same "down tree" selection */
+                    /* (If it has a "down tree") */
+                    else if(stop_span->down) {
+                        /* Release "down tree" information */
+                        H5S__hyper_free_span_info(stop_span->down);
 
-                    /* Advance to next span to check */
-                    tmp2_span=tmp2_span->next;
-                } /* end while */
-            } /* end if */
+                        /* Point at earlier span's "down tree" */
+                        stop_span->down = tmp_span->down;
+
+                        /* Increment reference count on shared "down tree" */
+                        stop_span->down->count++;
+                    } /* end else */
+
+                    /* Found span to merge into, break out now */
+                    break;
+                } /* end if */
+
+                /* Advance to next span to check */
+                tmp_span = tmp_span->next;
+            } /* end while */
         } /* end if */
-        else {
-            if(NULL == (new_span = H5S__hyper_new_span(coords[0], coords[0], NULL, NULL)))
-                HGOTO_ERROR(H5E_RESOURCE, H5E_NOSPACE, FAIL, "can't allocate hyperslab span")
+    } /* end if */
+    else {
+        unsigned u;                     /* Local index variable */
 
-            /* Add new span tree as span */
-            HDassert(tmp_span);
-            tmp_span->next=new_span;
+        /* Check if we made it all the way to the bottom span list in the tree
+         *      and the new coordinate adjoins the current tail span.
+         */
+        if(rank == 1 && (tail_span->high + 1) == coords[0])
+            /* Append element to current tail span */
+            tail_span->high++;
+        else {
+            H5S_hyper_span_t *new_span;     /* New span created for element */
 
-            /* Make scratch pointer point to last span in list */
-            tspan_info->scratch=(H5S_hyper_span_info_t *)new_span;
+            /* Make span tree for current coordinate(s) */
+            if(NULL == (new_span = H5S__hyper_coord_to_span(rank, coords)))
+                HGOTO_ERROR(H5E_DATASPACE, H5E_CANTALLOC, FAIL, "can't allocate hyperslab spans for coordinate")
 
-            /* Set the proper 'pstride' for new span */
-            new_span->pstride = new_span->low - tmp_span->low;
+            /* Add new span to span tree list */
+            tail_span->next = new_span;
+            span_tree->tail = new_span;
         } /* end else */
+
+        /* Update high bound for current span tree */
+        HDassert(coords[0] > span_tree->high_bounds[0]);
+        span_tree->high_bounds[0] = coords[0];
+
+        /* Update high bounds for dimensions below this one */
+        for(u = 1; u < rank; u++)
+            if(coords[u] > span_tree->high_bounds[u])
+                span_tree->high_bounds[u] = coords[u];
+
+        /* Need to signal to higher dimensions that high bounds changed */
+        *first_dim_modified = 0;
     } /* end else */
 
 done:
@@ -3907,6 +5894,24 @@ done:
  GLOBAL VARIABLES
  COMMENTS, BUGS, ASSUMPTIONS
     Assumes that the element is not already in the dataspace's selection
+
+    NOTE: There's also an assumption about the context of this function call -
+        This function is only called is only being called from H5D_chunk_mem_cb
+        in src/H5Dchunk.c, when the library is iterating over a memory
+        selection, so the coordinates passed to H5S_hyper_add_span_element will
+        always be in increasing order (according to a row-major (i.e. C, not
+        FORTRAN) scan) over the dataset. Therefore, for every input of
+        coordinates, only the last span element (i.e., the tail pointer) in
+        one dimension is checked against the input.
+
+    NOTE: This algorithm is definitely "correct" and tries to conserve memory
+        as much as possible, but it's doing a _lot_ of work that might be
+        better spent running a similar algorithm to "condense" the span tree
+        (possibly even back into a regular selection) just before the selection
+        is used for I/O on the chunk.  I'm not going to spend the time on this
+        currently, but it does sound like a good direction to explore.
+        QAK, 2019/01/24
+
  EXAMPLES
  REVISION LOG
 --------------------------------------------------------------------------*/
@@ -3926,9 +5931,13 @@ H5S_hyper_add_span_element(H5S_t *space, unsigned rank, const hsize_t *coords)
     /* Check if this is the first element in the selection */
     if(NULL == space->select.sel_info.hslab) {
         /* Allocate a span info node */
-        if(NULL == (head = H5FL_CALLOC(H5S_hyper_span_info_t)))
+        if(NULL == (head = H5S__hyper_new_span_info(rank)))
             HGOTO_ERROR(H5E_DATASPACE, H5E_CANTALLOC, FAIL, "can't allocate hyperslab span info")
 
+        /* Set the low & high bounds for this span info node */
+        H5MM_memcpy(head->low_bounds, coords, rank * sizeof(hsize_t));
+        H5MM_memcpy(head->high_bounds, coords, rank * sizeof(hsize_t));
+
         /* Set the reference count */
         head->count = 1;
 
@@ -3936,6 +5945,9 @@ H5S_hyper_add_span_element(H5S_t *space, unsigned rank, const hsize_t *coords)
         if(NULL == (head->head = H5S__hyper_coord_to_span(rank, coords)))
             HGOTO_ERROR(H5E_DATASPACE, H5E_CANTALLOC, FAIL, "can't allocate hyperslab spans for coordinate")
 
+        /* Update the tail pointer of this newly created span in dimension "rank" */
+        head->tail = head->head;
+
         /* Allocate selection info */
         if(NULL == (space->select.sel_info.hslab = H5FL_MALLOC(H5S_hyper_sel_t)))
             HGOTO_ERROR(H5E_DATASPACE, H5E_CANTALLOC, FAIL, "can't allocate hyperslab selection")
@@ -3956,7 +5968,10 @@ H5S_hyper_add_span_element(H5S_t *space, unsigned rank, const hsize_t *coords)
         space->select.num_elem = 1;
     } /* end if */
     else {
-        if(H5S__hyper_add_span_element_helper(space->select.sel_info.hslab->span_lst, rank, coords) < 0)
+        int first_dim_modified = -1;            /* Index of first dimension modified */
+
+        /* Add the element to the current set of spans */
+        if(H5S__hyper_add_span_element_helper(space->select.sel_info.hslab->span_lst, rank, coords, &first_dim_modified) < 0)
             HGOTO_ERROR(H5E_DATASPACE, H5E_CANTINSERT, FAIL, "can't insert coordinate into span tree")
 
         /* Increment # of elements in selection */
@@ -3974,120 +5989,19 @@ done:
 
 /*--------------------------------------------------------------------------
  NAME
-    H5S_hyper_reset_scratch
- PURPOSE
-    Reset the scratch information for span tree
- USAGE
-    herr_t H5S_hyper_reset_scratch(space)
-        H5S_t *space;           IN/OUT: Pointer to dataspace to reset scratch pointers
- RETURNS
-    Non-negative on success, negative on failure
- DESCRIPTION
-    Resets the "scratch" pointers used for various tasks in computing hyperslab
-    spans.
- GLOBAL VARIABLES
- COMMENTS, BUGS, ASSUMPTIONS
- EXAMPLES
- REVISION LOG
---------------------------------------------------------------------------*/
-herr_t
-H5S_hyper_reset_scratch(H5S_t *space)
-{
-    herr_t      ret_value = SUCCEED;       /* Return value */
-
-    FUNC_ENTER_NOAPI(FAIL)
-
-    HDassert(space);
-
-    /* Check if there are spans in the span tree */
-    if(space->select.sel_info.hslab->span_lst != NULL)
-        /* Reset the scratch pointers for the next routine which needs them */
-        H5S__hyper_span_scratch(space->select.sel_info.hslab->span_lst);
-
-done:
-    FUNC_LEAVE_NOAPI(ret_value)
-} /* end H5S_hyper_reset_scratch() */
-
-
-/*--------------------------------------------------------------------------
- NAME
-    H5S_hyper_convert
- PURPOSE
-    Convert a compatible selection to span tree form
- USAGE
-    herr_t H5S_hyper_convert(space)
-        H5S_t *space;           IN/OUT: Pointer to dataspace to convert
- RETURNS
-    Non-negative on success, negative on failure
- DESCRIPTION
-    Converts a compatible selection (currently only "all" selections) to the
-    span-tree form of a hyperslab selection. (Point and "none" selection aren't
-    currently supported and hyperslab selection always have the span-tree form
-    available).
- GLOBAL VARIABLES
- COMMENTS, BUGS, ASSUMPTIONS
- EXAMPLES
- REVISION LOG
---------------------------------------------------------------------------*/
-herr_t
-H5S_hyper_convert(H5S_t *space)
-{
-    herr_t      ret_value = SUCCEED;       /* Return value */
-
-    FUNC_ENTER_NOAPI(FAIL)
-
-    HDassert(space);
-
-    /* Check the type of selection */
-    switch(H5S_GET_SELECT_TYPE(space)) {
-        case H5S_SEL_ALL:    /* All elements selected in dataspace */
-            /* Convert current "all" selection to "real" hyperslab selection */
-            {
-                const hsize_t *tmp_start;       /* Temporary start information */
-                const hsize_t *tmp_stride;      /* Temporary stride information */
-                const hsize_t *tmp_count;       /* Temporary count information */
-                const hsize_t *tmp_block;       /* Temporary block information */
-
-                /* Set up temporary information for the dimensions */
-                tmp_start = H5S_hyper_zeros_g;
-                tmp_stride = tmp_count = H5S_hyper_ones_g;
-                tmp_block = space->extent.size;
-
-                /* Convert to hyperslab selection */
-                if(H5S_select_hyperslab(space,H5S_SELECT_SET,tmp_start,tmp_stride,tmp_count,tmp_block)<0)
-                    HGOTO_ERROR(H5E_DATASPACE, H5E_CANTSET, FAIL, "can't convert selection")
-            } /* end case */
-            break;
-
-        case H5S_SEL_HYPERSLABS:        /* Hyperslab selection */
-            break;
-
-        case H5S_SEL_NONE:   /* No elements selected in dataspace */
-        case H5S_SEL_POINTS: /* Point selection */
-        case H5S_SEL_ERROR:  /* Selection error */
-        case H5S_SEL_N:      /* Selection count */
-        default:
-            HGOTO_ERROR(H5E_ARGS, H5E_UNSUPPORTED, FAIL, "can't convert to span tree selection")
-    } /* end switch */
-
-done:
-    FUNC_LEAVE_NOAPI(ret_value)
-} /* end H5S_hyper_convert() */
-
-
-/*--------------------------------------------------------------------------
- NAME
     H5S__hyper_intersect_block_helper
  PURPOSE
     Helper routine to detect intersections in span trees
  USAGE
-    htri_t H5S_hyper_intersect_block_helper(spans, start, end)
+    hbool_t H5S__hyper_intersect_block_helper(spans, rank, start, end, op_info_i, op_gen)
         H5S_hyper_span_info_t *spans;     IN: First span tree to operate with
-        hssize_t *offset;   IN: Selection offset coordinate
+        unsigned rank;     IN: Number of dimensions for span tree
         hsize_t *start;    IN: Starting coordinate for block
         hsize_t *end;      IN: Ending coordinate for block
+        unsigned op_info_i;             IN: Index of op info to use
+        uint64_t op_gen;   IN: Operation generation
  RETURN
-    Non-negative on success, negative on failure
+    Non-negative (TRUE/FALSE) on success, can't fail
  DESCRIPTION
     Quickly detect intersections between span tree and block
  GLOBAL VARIABLES
@@ -4096,10 +6010,10 @@ done:
  REVISION LOG
 --------------------------------------------------------------------------*/
 static hbool_t
-H5S__hyper_intersect_block_helper(const H5S_hyper_span_info_t *spans,
-    const hsize_t *start, const hsize_t *end)
+H5S__hyper_intersect_block_helper(H5S_hyper_span_info_t *spans,
+    unsigned rank, const hsize_t *start, const hsize_t *end, unsigned op_info_i,
+    uint64_t op_gen)
 {
-    H5S_hyper_span_t *curr;         /* Pointer to current span in 1st span tree */
     hbool_t ret_value = FALSE;      /* Return value */
 
     FUNC_ENTER_STATIC_NOERR
@@ -4109,37 +6023,52 @@ H5S__hyper_intersect_block_helper(const H5S_hyper_span_info_t *spans,
     HDassert(start);
     HDassert(end);
 
-    /* Get the span list for spans in this tree */
-    curr = spans->head;
-
-    /* Iterate over the spans in the tree */
-    while(curr != NULL) {
-        /* Check for span entirely before block */
-        if(curr->high < *start)
-            /* Advance to next span in this dimension */
-            curr = curr->next;
-        /* If this span is past the end of the block, then we're done in this dimension */
-        else if(curr->low > *end)
-            HGOTO_DONE(FALSE)
-        /* block & span overlap */
-        else {
-            if(curr->down == NULL)
-                HGOTO_DONE(TRUE)
-            else {
-                hbool_t status;         /* Status from recursive call */
+    /* Check if we've already visited this span tree */
+    if(spans->op_info[op_info_i].op_gen != op_gen) {
+        H5S_hyper_span_t *curr;         /* Pointer to current span in 1st span tree */
+        unsigned u;                     /* Local index variable */
 
-                /* Recursively check spans in next dimension down */
-                status = H5S__hyper_intersect_block_helper(curr->down, start + 1, end + 1);
+        /* Verify that there is a possibility of an overlap by checking the block
+         *  against the low & high bounds for the span tree.
+         */
+        for(u = 0; u < rank; u++)
+            if(start[u] > spans->high_bounds[u] || end[u] < spans->low_bounds[u])
+                HGOTO_DONE(FALSE)
 
-                /* If there is a span intersection in the down dimensions, the span trees overlap */
-                if(status == TRUE)
-                    HGOTO_DONE(TRUE);
+        /* Get the span list for spans in this tree */
+        curr = spans->head;
 
-                /* No intersection in down dimensions, advance to next span */
+        /* Iterate over the spans in the tree */
+        while(curr != NULL) {
+            /* Check for span entirely before block */
+            if(curr->high < *start)
+                /* Advance to next span in this dimension */
                 curr = curr->next;
+            /* If this span is past the end of the block, then we're done in this dimension */
+            else if(curr->low > *end)
+                HGOTO_DONE(FALSE)
+            /* block & span overlap */
+            else {
+                /* If this is the bottom dimension, then the span tree overlaps the block */
+                if(curr->down == NULL)
+                    HGOTO_DONE(TRUE)
+                /* Recursively check spans in next dimension down */
+                else {
+                    /* If there is an intersection in the "down" dimensions,
+                     * the span trees overlap.
+                     */
+                    if(H5S__hyper_intersect_block_helper(curr->down, rank - 1, start + 1, end + 1, op_info_i, op_gen))
+                        HGOTO_DONE(TRUE)
+
+                    /* No intersection in down dimensions, advance to next span */
+                    curr = curr->next;
+                } /* end else */
             } /* end else */
-        } /* end else */
-    } /* end while */
+        } /* end while */
+
+        /* Set the tree's operation generation */
+        spans->op_info[op_info_i].op_gen = op_gen;
+    } /* end if */
 
     /* Fall through with 'FALSE' return value */
 
@@ -4150,51 +6079,134 @@ done:
 
 /*--------------------------------------------------------------------------
  NAME
-    H5S_hyper_intersect_block
+    H5S__hyper_intersect_block
  PURPOSE
-    Detect intersections in span trees
+    Detect intersections of selection with block
  USAGE
-    htri_t H5S_hyper_intersect_block(space, start, end)
-        H5S_t *space;       IN: First dataspace to operate on span tree
-        hssize_t *start;    IN: Starting coordinate for block
-        hssize_t *end;      IN: Ending coordinate for block
+    htri_t H5S__hyper_intersect_block(space, start, end)
+        const H5S_t *space;     IN: Dataspace with selection to use
+        const hsize_t *start;   IN: Starting coordinate for block
+        const hsize_t *end;     IN: Ending coordinate for block
  RETURNS
-    Non-negative on success, negative on failure
+    Non-negative TRUE / FALSE on success, negative on failure
  DESCRIPTION
-    Quickly detect intersections between span tree and block
+    Quickly detect intersections between both regular hyperslabs and span trees
+    with a block
  GLOBAL VARIABLES
  COMMENTS, BUGS, ASSUMPTIONS
+    Does not use selection offset.
  EXAMPLES
  REVISION LOG
 --------------------------------------------------------------------------*/
-htri_t
-H5S_hyper_intersect_block(H5S_t *space, const hsize_t *start, const hsize_t *end)
+static htri_t
+H5S__hyper_intersect_block(const H5S_t *space, const hsize_t *start, const hsize_t *end)
 {
     htri_t ret_value = FAIL;    /* Return value */
 
-    FUNC_ENTER_NOAPI(FAIL)
+    FUNC_ENTER_STATIC_NOERR
 
     /* Sanity check */
     HDassert(space);
+    HDassert(H5S_SEL_HYPERSLABS == H5S_GET_SELECT_TYPE(space));
     HDassert(start);
     HDassert(end);
 
-    /* Check for 'all' selection, instead of a hyperslab selection */
-    /* (Technically, this shouldn't be in the "hyperslab" routines...) */
-    if(H5S_GET_SELECT_TYPE(space) == H5S_SEL_ALL)
-        HGOTO_DONE(TRUE);
+    /* Attempt to rebuild diminfo if it is invalid and has not been confirmed
+     * to be impossible.
+     */
+    if(space->select.sel_info.hslab->diminfo_valid == H5S_DIMINFO_VALID_NO)
+        H5S__hyper_rebuild((H5S_t *)space);     /* Casting away const OK -QAK */
 
-    /* Check that the space selection has a span tree */
-    if(NULL == space->select.sel_info.hslab->span_lst)
-        if(H5S__hyper_generate_spans(space) < 0)
-            HGOTO_ERROR(H5E_DATASPACE, H5E_UNINITIALIZED, FAIL, "dataspace does not have span tree")
+    /* Check for regular hyperslab intersection */
+    if(space->select.sel_info.hslab->diminfo_valid == H5S_DIMINFO_VALID_YES) {
+        hbool_t single_block;   /* Whether the regular selection is a single block */
+        unsigned u;             /* Local index variable */
 
-    /* Perform the span-by-span intersection check */
-    ret_value = H5S__hyper_intersect_block_helper(space->select.sel_info.hslab->span_lst, start, end);
+        /* Check for a single block */
+        /* For a regular hyperslab to be single, it must have only one block
+         * (i.e. count == 1 in all dimensions).
+         */
+        single_block = TRUE;
+        for(u = 0; u < space->extent.rank; u++)
+            if(space->select.sel_info.hslab->diminfo.opt[u].count > 1)
+                single_block = FALSE;
+
+        /* Single blocks have already been "compared" above, in the low / high
+         * bound checking, so just return TRUE if we've reached here - they
+         * would have been rejected earlier, if they didn't intersect.
+         */
+        if(single_block)
+            HGOTO_DONE(TRUE)
+        else {
+            /* Loop over the dimensions, checking for an intersection */
+            for(u = 0; u < space->extent.rank; u++) {
+                /* If the block's start is <= the hyperslab start, they intersect */
+                /* (So, if the start is > the hyperslab start, check more conditions) */
+                if(start[u] > space->select.sel_info.hslab->diminfo.opt[u].start) {
+                    hsize_t adj_start;  /* Start coord, adjusted for hyperslab selection parameters */
+                    hsize_t nstride;    /* Number of strides into the selection */
+
+                    /* Adjust start coord for selection's 'start' offset */
+                    adj_start = start[u] - space->select.sel_info.hslab->diminfo.opt[u].start;
+
+                    /* Compute # of strides into the selection */
+                    if(space->select.sel_info.hslab->diminfo.opt[u].count > 1)
+                        nstride = adj_start / space->select.sel_info.hslab->diminfo.opt[u].stride;
+                    else
+                        nstride = 0;
+
+                    /* Sanity check */
+                    HDassert(nstride <= space->select.sel_info.hslab->diminfo.opt[u].count);
+
+                    /* "Rebase" the adjusted start coord into the same range
+                     *      range of values as the selections's first block.
+                     */
+                    adj_start -= nstride * space->select.sel_info.hslab->diminfo.opt[u].stride;
+
+                    /* If the adjusted start doesn't fall within the first hyperslab
+                     *  span, check for the block overlapping with the next one.
+                     */
+                    if(adj_start >= space->select.sel_info.hslab->diminfo.opt[u].block) {
+                        hsize_t adj_end;    /* End coord, adjusted for hyperslab selection parameters */
+
+                        /* Adjust end coord for selection's 'start' offset */
+                        adj_end = end[u] - space->select.sel_info.hslab->diminfo.opt[u].start;
+
+                        /* "Rebase" the adjusted end coord into the same range
+                         *      range of values as the selections's first block.
+                         */
+                        adj_end -= nstride * space->select.sel_info.hslab->diminfo.opt[u].stride;
+
+                        /* If block doesn't extend over beginning of next span,
+                         *  it doesn't intersect.
+                         */
+                        if(adj_end < space->select.sel_info.hslab->diminfo.opt[u].stride)
+                            HGOTO_DONE(FALSE)
+                    } /* end if */
+                } /* end if */
+            } /* end for */
+
+            /* If we've looped through all dimensions and none of them didn't
+             *  overlap, then all of them do, so we report TRUE.
+             */
+            HGOTO_DONE(TRUE)
+        } /* end else */
+    } /* end if */
+    else {
+        uint64_t op_gen;            /* Operation generation value */
+
+        /* Acquire an operation generation value for this operation */
+        op_gen = H5S__hyper_get_op_gen();
+
+        /* Perform the span-by-span intersection check */
+        /* Always use op_info[0] since we own this op_info, so there can be no
+         * simultaneous operations */
+        ret_value = H5S__hyper_intersect_block_helper(space->select.sel_info.hslab->span_lst, space->extent.rank, start, end, 0, op_gen);
+    } /* end else */
 
 done:
     FUNC_LEAVE_NOAPI(ret_value)
-} /* end H5S_hyper_intersect_block() */
+} /* end H5S__hyper_intersect_block() */
 
 
 /*--------------------------------------------------------------------------
@@ -4203,9 +6215,12 @@ done:
  PURPOSE
     Helper routine to adjust offsets in span trees
  USAGE
-    void H5S__hyper_adjust_u_helper(spans, offset)
+    void H5S__hyper_adjust_u_helper(spans, rank, offset, op_info_i, op_gen)
         H5S_hyper_span_info_t *spans;   IN: Span tree to operate with
+        unsigned rank;                  IN: Number of dimensions for span tree
         const hsize_t *offset;          IN: Offset to subtract
+        unsigned op_info_i;             IN: Index of op info to use
+        uint64_t op_gen;                IN: Operation generation
  RETURNS
     None
  DESCRIPTION
@@ -4216,23 +6231,26 @@ done:
  REVISION LOG
 --------------------------------------------------------------------------*/
 static void
-H5S__hyper_adjust_u_helper(H5S_hyper_span_info_t *spans,
-    const hsize_t *offset)
+H5S__hyper_adjust_u_helper(H5S_hyper_span_info_t *spans, unsigned rank,
+    const hsize_t *offset, unsigned op_info_i, uint64_t op_gen)
 {
     FUNC_ENTER_STATIC_NOERR
 
     /* Sanity checks */
     HDassert(spans);
-    HDassert(spans->scratch == (H5S_hyper_span_info_t *)~((size_t)NULL) ||
-        spans->scratch == NULL);
     HDassert(offset);
 
-    /* Check if we've already set this down span tree */
-    if(spans->scratch != (H5S_hyper_span_info_t *)~((size_t)NULL)) {
+    /* Check if we've already set this span tree */
+    if(spans->op_info[op_info_i].op_gen != op_gen) {
         H5S_hyper_span_t *span;     /* Pointer to current span in span tree */
+        unsigned u;                 /* Local index variable */
 
-        /* Set the tree's scratch pointer */
-        spans->scratch = (H5S_hyper_span_info_t *)~((size_t)NULL);
+        /* Adjust the span tree's low & high bounds */
+        for(u = 0; u < rank; u++) {
+            HDassert(spans->low_bounds[u] >= offset[u]);
+            spans->low_bounds[u] -= offset[u];
+            spans->high_bounds[u] -= offset[u];
+        } /* end for */
 
         /* Iterate over the spans in tree */
         span = spans->head;
@@ -4244,11 +6262,14 @@ H5S__hyper_adjust_u_helper(H5S_hyper_span_info_t *spans,
 
             /* Recursively adjust spans in next dimension down */
             if(span->down != NULL)
-                H5S__hyper_adjust_u_helper(span->down, offset + 1);
+                H5S__hyper_adjust_u_helper(span->down, rank - 1, offset + 1, op_info_i, op_gen);
 
             /* Advance to next span in this dimension */
             span = span->next;
         } /* end while */
+
+        /* Set the tree's operation generation */
+        spans->op_info[op_info_i].op_gen = op_gen;
     } /* end if */
 
     FUNC_LEAVE_NOAPI_VOID
@@ -4295,19 +6316,30 @@ H5S__hyper_adjust_u(H5S_t *space, const hsize_t *offset)
     /* Only perform operation if the offset is non-zero */
     if(non_zero_offset) {
         /* Subtract the offset from the "regular" coordinates, if they exist */
+        /* (No need to rebuild the dimension info yet -QAK) */
         if(space->select.sel_info.hslab->diminfo_valid == H5S_DIMINFO_VALID_YES) {
             for(u = 0; u < space->extent.rank; u++) {
                 HDassert(space->select.sel_info.hslab->diminfo.opt[u].start >= offset[u]);
                 space->select.sel_info.hslab->diminfo.opt[u].start -= offset[u];
+
+                /* Adjust the low & high bounds */
+                HDassert(space->select.sel_info.hslab->diminfo.low_bounds[u] >= offset[u]);
+                space->select.sel_info.hslab->diminfo.low_bounds[u] -= offset[u];
+                space->select.sel_info.hslab->diminfo.high_bounds[u] -= offset[u];
             } /* end for */
         } /* end if */
 
         /* Subtract the offset from the span tree coordinates, if they exist */
         if(space->select.sel_info.hslab->span_lst) {
-            H5S__hyper_adjust_u_helper(space->select.sel_info.hslab->span_lst, offset);
+            uint64_t op_gen;            /* Operation generation value */
 
-            /* Reset the scratch pointers for the next routine which needs them */
-            H5S__hyper_span_scratch(space->select.sel_info.hslab->span_lst);
+            /* Acquire an operation generation value for this operation */
+            op_gen = H5S__hyper_get_op_gen();
+
+            /* Perform adjustment */
+            /* Always use op_info[0] since we own this op_info, so there can be no
+             * simultaneous operations */
+            H5S__hyper_adjust_u_helper(space->select.sel_info.hslab->span_lst, space->extent.rank, offset, 0, op_gen);
         } /* end if */
     } /* end if */
 
@@ -4316,14 +6348,14 @@ H5S__hyper_adjust_u(H5S_t *space, const hsize_t *offset)
 
 
 /*-------------------------------------------------------------------------
- * Function:	H5S__hyper_project_scalar
+ * Function:    H5S__hyper_project_scalar
  *
- * Purpose:	Projects a single element hyperslab selection into a scalar
+ * Purpose:    Projects a single element hyperslab selection into a scalar
  *              dataspace
  *
- * Return:	non-negative on success, negative on failure.
+ * Return:    Non-negative on success, negative on failure.
  *
- * Programmer:	Quincey Koziol
+ * Programmer:    Quincey Koziol
  *              Sunday, July 18, 2010
  *
  *-------------------------------------------------------------------------
@@ -4340,12 +6372,20 @@ H5S__hyper_project_scalar(const H5S_t *space, hsize_t *offset)
     HDassert(offset);
 
     /* Check for a "regular" hyperslab selection */
+    /* (No need to rebuild the dimension info yet -QAK) */
     if(space->select.sel_info.hslab->diminfo_valid == H5S_DIMINFO_VALID_YES) {
         const H5S_hyper_dim_t *diminfo = space->select.sel_info.hslab->diminfo.opt; /* Alias for dataspace's diminfo information */
         unsigned u;                 /* Counter */
 
         /* Build the table of the initial offset */
         for(u = 0; u < space->extent.rank; u++) {
+            /* Sanity check diminfo */
+            HDassert(1 == diminfo[u].count);
+            HDassert(1 == diminfo[u].block);
+
+            /* Sanity check bounds, while we're here */
+            HDassert(diminfo[u].start == space->select.sel_info.hslab->diminfo.low_bounds[u]);
+
             /* Keep the offset for later */
             block[u] = diminfo[u].start;
         } /* end for */
@@ -4357,17 +6397,22 @@ H5S__hyper_project_scalar(const H5S_t *space, hsize_t *offset)
         /* Advance down selected spans */
         curr = space->select.sel_info.hslab->span_lst->head;
         curr_dim = 0;
-        while(curr) {
-            /* Sanity check for more than one span */
+        while(1) {
+            /* Sanity checks */
             HDassert(NULL == curr->next);
             HDassert(curr->low == curr->high);
+            HDassert(curr_dim < space->extent.rank);
 
             /* Save the location of the selection in current dimension */
             block[curr_dim] = curr->low;
 
             /* Advance down to next dimension */
-            curr = curr->down->head;
-            curr_dim++;
+            if(curr->down) {
+                curr = curr->down->head;
+                curr_dim++;
+            } /* end if */
+            else
+                break;
         } /* end while */
     } /* end else */
 
@@ -4379,14 +6424,14 @@ H5S__hyper_project_scalar(const H5S_t *space, hsize_t *offset)
 
 
 /*-------------------------------------------------------------------------
- * Function:	H5S__hyper_project_simple_lower
+ * Function:    H5S__hyper_project_simple_lower
  *
- * Purpose:	Projects a hyperslab selection onto/into a simple dataspace
+ * Purpose:    Projects a hyperslab selection onto/into a simple dataspace
  *              of a lower rank
  *
- * Return:	non-negative on success, negative on failure.
+ * Return:    Non-negative on success, negative on failure.
  *
- * Programmer:	Quincey Koziol
+ * Programmer:    Quincey Koziol
  *              Sunday, July 18, 2010
  *
  *-------------------------------------------------------------------------
@@ -4426,14 +6471,14 @@ H5S__hyper_project_simple_lower(const H5S_t *base_space, H5S_t *new_space)
 
 
 /*-------------------------------------------------------------------------
- * Function:	H5S__hyper_project_simple_higher
+ * Function:    H5S__hyper_project_simple_higher
  *
- * Purpose:	Projects a hyperslab selection onto/into a simple dataspace
+ * Purpose:    Projects a hyperslab selection onto/into a simple dataspace
  *              of a higher rank
  *
- * Return:	non-negative on success, negative on failure.
+ * Return:    Non-negative on success, negative on failure.
  *
- * Programmer:	Quincey Koziol
+ * Programmer:    Quincey Koziol
  *              Sunday, July 18, 2010
  *
  *-------------------------------------------------------------------------
@@ -4442,7 +6487,9 @@ static herr_t
 H5S__hyper_project_simple_higher(const H5S_t *base_space, H5S_t *new_space)
 {
     H5S_hyper_span_t *prev_span = NULL; /* Pointer to previous list of spans */
+    unsigned delta_rank;                /* Difference in dataspace ranks */
     unsigned curr_dim;                  /* Current dimension being operated on */
+    unsigned u;                         /* Local index variable */
     herr_t ret_value = SUCCEED;         /* Return value */
 
     FUNC_ENTER_STATIC
@@ -4455,15 +6502,15 @@ H5S__hyper_project_simple_higher(const H5S_t *base_space, H5S_t *new_space)
     /* Create nodes until reaching the correct # of dimensions */
     new_space->select.sel_info.hslab->span_lst = NULL;
     curr_dim = 0;
-    while(curr_dim < (new_space->extent.rank - base_space->extent.rank)) {
+    delta_rank = (new_space->extent.rank - base_space->extent.rank);
+    while(curr_dim < delta_rank) {
         H5S_hyper_span_info_t *new_span_info;  /* Pointer to list of spans */
         H5S_hyper_span_t *new_span;     /* Temporary hyperslab span */
 
         /* Allocate a new span_info node */
-        if(NULL == (new_span_info = H5FL_CALLOC(H5S_hyper_span_info_t))) {
+        if(NULL == (new_span_info = H5S__hyper_new_span_info(new_space->extent.rank))) {
             if(prev_span)
-                if(H5S__hyper_free_span(prev_span) < 0)
-                    HERROR(H5E_DATASPACE, H5E_CANTFREE, "can't free hyperslab span");
+                H5S__hyper_free_span(prev_span);
             HGOTO_ERROR(H5E_DATASPACE, H5E_CANTALLOC, FAIL, "can't allocate hyperslab span info")
         } /* end if */
 
@@ -4475,13 +6522,24 @@ H5S__hyper_project_simple_higher(const H5S_t *base_space, H5S_t *new_space)
         if(NULL == (new_span = H5S__hyper_new_span((hsize_t)0, (hsize_t)0, NULL, NULL))) {
             HDassert(new_span_info);
             if(!prev_span)
-                (void)H5FL_FREE(H5S_hyper_span_info_t, new_span_info);
+                (void)H5FL_ARR_FREE(hbounds_t, new_span_info);
             HGOTO_ERROR(H5E_DATASPACE, H5E_CANTALLOC, FAIL, "can't allocate hyperslab span")
         } /* end if */
 
         /* Set the span_info information */
         new_span_info->count = 1;
         new_span_info->head = new_span;
+        new_span_info->tail = new_span;
+
+        /* Set the bounding box */
+        for(u = 0; u < delta_rank; u++) {
+            new_span_info->low_bounds[u] = 0;
+            new_span_info->high_bounds[u] = 0;
+        } /* end for */
+        for(; u < new_space->extent.rank; u++) {
+            new_span_info->low_bounds[u] = base_space->select.sel_info.hslab->span_lst->low_bounds[u - delta_rank];
+            new_span_info->high_bounds[u] = base_space->select.sel_info.hslab->span_lst->high_bounds[u - delta_rank];
+        } /* end for */
 
         /* Attach to new space, if top span info */
         if(NULL == new_space->select.sel_info.hslab->span_lst)
@@ -4503,10 +6561,9 @@ H5S__hyper_project_simple_higher(const H5S_t *base_space, H5S_t *new_space)
 done:
     if(ret_value < 0 && new_space->select.sel_info.hslab->span_lst) {
         if(new_space->select.sel_info.hslab->span_lst->head)
-            if(H5S__hyper_free_span(new_space->select.sel_info.hslab->span_lst->head) < 0)
-                HDONE_ERROR(H5E_DATASPACE, H5E_CANTFREE, FAIL, "can't free hyperslab span")
+            H5S__hyper_free_span(new_space->select.sel_info.hslab->span_lst->head);
 
-        new_space->select.sel_info.hslab->span_lst = H5FL_FREE(H5S_hyper_span_info_t, new_space->select.sel_info.hslab->span_lst);
+        new_space->select.sel_info.hslab->span_lst = (H5S_hyper_span_info_t *)H5FL_ARR_FREE(hbounds_t, new_space->select.sel_info.hslab->span_lst);
     } /* end if */
 
     FUNC_LEAVE_NOAPI(ret_value)
@@ -4514,20 +6571,21 @@ done:
 
 
 /*-------------------------------------------------------------------------
- * Function:	H5S__hyper_project_simple
+ * Function:    H5S__hyper_project_simple
  *
- * Purpose:	Projects a hyperslab selection onto/into a simple dataspace
+ * Purpose:    Projects a hyperslab selection onto/into a simple dataspace
  *              of a different rank
  *
- * Return:	non-negative on success, negative on failure.
+ * Return:    Non-negative on success, negative on failure.
  *
- * Programmer:	Quincey Koziol
+ * Programmer:    Quincey Koziol
  *              Sunday, July 18, 2010
  *
  *-------------------------------------------------------------------------
  */
 static herr_t
-H5S__hyper_project_simple(const H5S_t *base_space, H5S_t *new_space, hsize_t *offset)
+H5S__hyper_project_simple(const H5S_t *base_space, H5S_t *new_space,
+    hsize_t *offset)
 {
     herr_t ret_value = SUCCEED;         /* Return value */
 
@@ -4550,15 +6608,16 @@ H5S__hyper_project_simple(const H5S_t *base_space, H5S_t *new_space, hsize_t *of
     new_space->select.sel_info.hslab->unlim_dim = -1;
 
     /* Check for a "regular" hyperslab selection */
+    /* (No need to rebuild the dimension info yet -QAK) */
     if(base_space->select.sel_info.hslab->diminfo_valid == H5S_DIMINFO_VALID_YES) {
         unsigned base_space_dim;    /* Current dimension in the base dataspace */
         unsigned new_space_dim;     /* Current dimension in the new dataspace */
+        unsigned u;                 /* Local index variable */
 
         /* Check if the new space's rank is < or > base space's rank */
         if(new_space->extent.rank < base_space->extent.rank) {
             const H5S_hyper_dim_t *opt_diminfo = base_space->select.sel_info.hslab->diminfo.opt; /* Alias for dataspace's diminfo information */
             hsize_t block[H5S_MAX_RANK];     /* Block selected in base dataspace */
-            unsigned u;         /* Local index variable */
 
             /* Compute the offset for the down-projection */
             HDmemset(block, 0, sizeof(block));
@@ -4618,6 +6677,12 @@ H5S__hyper_project_simple(const H5S_t *base_space, H5S_t *new_space, hsize_t *of
             new_space_dim++;
         } /* end for */
 
+        /* Update the bounding box */
+        for(u = 0; u < new_space->extent.rank; u++) {
+            new_space->select.sel_info.hslab->diminfo.low_bounds[u] = new_space->select.sel_info.hslab->diminfo.opt[u].start;
+            new_space->select.sel_info.hslab->diminfo.high_bounds[u] = new_space->select.sel_info.hslab->diminfo.low_bounds[u] + new_space->select.sel_info.hslab->diminfo.opt[u].stride * (new_space->select.sel_info.hslab->diminfo.opt[u].count - 1) + (new_space->select.sel_info.hslab->diminfo.opt[u].block - 1);
+        } /* end for */
+
         /* Indicate that the dimension information is valid */
         new_space->select.sel_info.hslab->diminfo_valid = H5S_DIMINFO_VALID_YES;
 
@@ -4664,8 +6729,8 @@ H5S__hyper_project_simple(const H5S_t *base_space, H5S_t *new_space, hsize_t *of
                 HGOTO_ERROR(H5E_DATASPACE, H5E_CANTSELECT, FAIL, "can't project hyperslab selection into less dimensions")
         } /* end else */
 
-        /* Indicate that the dimension information is not valid */
-        new_space->select.sel_info.hslab->diminfo_valid = H5S_DIMINFO_VALID_NO;
+        /* Copy the status of the dimension information */
+        new_space->select.sel_info.hslab->diminfo_valid = base_space->select.sel_info.hslab->diminfo_valid;
     } /* end else */
 
     /* Number of elements selected will be the same */
@@ -4685,9 +6750,12 @@ done:
  PURPOSE
     Helper routine to adjust offsets in span trees
  USAGE
-    void H5S__hyper_adjust_s_helper(spans, offset)
+    void H5S__hyper_adjust_s_helper(spans, rank, offset, op_info_i, op_gen)
         H5S_hyper_span_info_t *spans;   IN: Span tree to operate with
+        unsigned rank;                  IN: Number of dimensions for span tree
         const hssize_t *offset;         IN: Offset to subtract
+        unsigned op_info_i;             IN: Index of op info to use
+        uint64_t op_gen;                IN: Operation generation
  RETURNS
     None
  DESCRIPTION
@@ -4698,23 +6766,26 @@ done:
  REVISION LOG
 --------------------------------------------------------------------------*/
 static void
-H5S__hyper_adjust_s_helper(H5S_hyper_span_info_t *spans,
-    const hssize_t *offset)
+H5S__hyper_adjust_s_helper(H5S_hyper_span_info_t *spans, unsigned rank,
+    const hssize_t *offset, unsigned op_info_i, uint64_t op_gen)
 {
     FUNC_ENTER_STATIC_NOERR
 
     /* Sanity checks */
     HDassert(spans);
-    HDassert(spans->scratch == (H5S_hyper_span_info_t *)~((size_t)NULL) ||
-        spans->scratch == NULL);
     HDassert(offset);
 
-    /* Check if we've already set this down span tree */
-    if(spans->scratch != (H5S_hyper_span_info_t *)~((size_t)NULL)) {
+    /* Check if we've already set this span tree */
+    if(spans->op_info[op_info_i].op_gen != op_gen) {
         H5S_hyper_span_t *span;     /* Pointer to current span in span tree */
+        unsigned u;                 /* Local index variable */
 
-        /* Set the tree's scratch pointer */
-        spans->scratch = (H5S_hyper_span_info_t *)~((size_t)NULL);
+        /* Adjust the span tree's low & high bounds */
+        for(u = 0; u < rank; u++) {
+            HDassert((hssize_t)spans->low_bounds[u] >= offset[u]);
+            spans->low_bounds[u] = (hsize_t)((hssize_t)spans->low_bounds[u] - offset[u]);
+            spans->high_bounds[u] = (hsize_t)((hssize_t)spans->high_bounds[u] - offset[u]);
+        } /* end for */
 
         /* Iterate over the spans in tree */
         span = spans->head;
@@ -4726,11 +6797,14 @@ H5S__hyper_adjust_s_helper(H5S_hyper_span_info_t *spans,
 
             /* Recursively adjust spans in next dimension down */
             if(span->down != NULL)
-                H5S__hyper_adjust_s_helper(span->down, offset + 1);
+                H5S__hyper_adjust_s_helper(span->down, rank - 1, offset + 1, op_info_i, op_gen);
 
             /* Advance to next span in this dimension */
             span = span->next;
         } /* end while */
+
+        /* Set the tree's operation generation */
+        spans->op_info[op_info_i].op_gen = op_gen;
     } /* end if */
 
     FUNC_LEAVE_NOAPI_VOID
@@ -4739,11 +6813,11 @@ H5S__hyper_adjust_s_helper(H5S_hyper_span_info_t *spans,
 
 /*--------------------------------------------------------------------------
  NAME
-    H5S_hyper_adjust_s
+    H5S__hyper_adjust_s
  PURPOSE
     Adjust a hyperslab selection by subtracting an offset
  USAGE
-    herr_t H5S_hyper_adjust_s(space,offset)
+    herr_t H5S__hyper_adjust_s(space,offset)
         H5S_t *space;           IN/OUT: Pointer to dataspace to adjust
         const hssize_t *offset; IN: Offset to subtract
  RETURNS
@@ -4755,8 +6829,8 @@ H5S__hyper_adjust_s_helper(H5S_hyper_span_info_t *spans,
  EXAMPLES
  REVISION LOG
 --------------------------------------------------------------------------*/
-herr_t
-H5S_hyper_adjust_s(H5S_t *space, const hssize_t *offset)
+static herr_t
+H5S__hyper_adjust_s(H5S_t *space, const hssize_t *offset)
 {
     hbool_t non_zero_offset = FALSE;    /* Whether any offset is non-zero */
     unsigned u;                         /* Local index variable */
@@ -4778,25 +6852,36 @@ H5S_hyper_adjust_s(H5S_t *space, const hssize_t *offset)
     /* Only perform operation if the offset is non-zero */
     if(non_zero_offset) {
         /* Subtract the offset from the "regular" coordinates, if they exist */
+        /* (No need to rebuild the dimension info yet -QAK) */
         if(space->select.sel_info.hslab->diminfo_valid == H5S_DIMINFO_VALID_YES) {
             for(u = 0; u < space->extent.rank; u++) {
                 HDassert((hssize_t)space->select.sel_info.hslab->diminfo.opt[u].start >= offset[u]);
                 space->select.sel_info.hslab->diminfo.opt[u].start = (hsize_t)((hssize_t)space->select.sel_info.hslab->diminfo.opt[u].start - offset[u]);
+
+                /* Adjust the low & high bounds */
+                HDassert((hssize_t)space->select.sel_info.hslab->diminfo.low_bounds[u] >= offset[u]);
+                space->select.sel_info.hslab->diminfo.low_bounds[u] = (hsize_t)((hssize_t)space->select.sel_info.hslab->diminfo.low_bounds[u] - offset[u]);
+                space->select.sel_info.hslab->diminfo.high_bounds[u] = (hsize_t)((hssize_t)space->select.sel_info.hslab->diminfo.high_bounds[u] - offset[u]);
             } /* end for */
         } /* end if */
 
         /* Subtract the offset from the span tree coordinates, if they exist */
         if(space->select.sel_info.hslab->span_lst) {
-            H5S__hyper_adjust_s_helper(space->select.sel_info.hslab->span_lst, offset);
+            uint64_t op_gen;            /* Operation generation value */
+
+            /* Acquire an operation generation value for this operation */
+            op_gen = H5S__hyper_get_op_gen();
 
-            /* Reset the scratch pointers for the next routine which needs them */
-            H5S__hyper_span_scratch(space->select.sel_info.hslab->span_lst);
+            /* Perform the adjustment */
+            /* Always use op_info[0] since we own this op_info, so there can be no
+             * simultaneous operations */
+            H5S__hyper_adjust_s_helper(space->select.sel_info.hslab->span_lst, space->extent.rank, offset, 0, op_gen);
         } /* end if */
     }
 
 done:
     FUNC_LEAVE_NOAPI(ret_value)
-} /* end H5S_hyper_adjust_s() */
+} /* end H5S__hyper_adjust_s() */
 
 
 /*--------------------------------------------------------------------------
@@ -4806,11 +6891,11 @@ done:
     "Normalize" a hyperslab selection by adjusting it's coordinates by the
     amount of the selection offset.
  USAGE
-    hbool_t H5S_hyper_normalize_offset(space, old_offset)
+    htri_t H5S_hyper_normalize_offset(space, old_offset)
         H5S_t *space;           IN/OUT: Pointer to dataspace to move
         hssize_t *old_offset;   OUT: Pointer to space to store old offset
  RETURNS
-    TRUE if space has been normalized, FALSE if not
+    TRUE/FALSE for hyperslab selection, FAIL on error
  DESCRIPTION
     Copies the current selection offset into the array provided, then
     inverts the selection offset, subtracts the offset from the hyperslab
@@ -4823,7 +6908,7 @@ done:
 htri_t
 H5S_hyper_normalize_offset(H5S_t *space, hssize_t *old_offset)
 {
-    htri_t ret_value = FALSE;           /* Return value */
+    htri_t ret_value = FALSE;          /* Return value */
 
     FUNC_ENTER_NOAPI(FAIL)
 
@@ -4842,7 +6927,7 @@ H5S_hyper_normalize_offset(H5S_t *space, hssize_t *old_offset)
         } /* end for */
 
         /* Call the 'adjust' routine */
-        if(H5S_hyper_adjust_s(space, space->select.offset) < 0)
+        if(H5S__hyper_adjust_s(space, space->select.offset) < 0)
             HGOTO_ERROR(H5E_DATASPACE, H5E_CANTSET, FAIL, "can't adjust selection")
 
         /* Zero out the selection offset */
@@ -4890,7 +6975,7 @@ H5S_hyper_denormalize_offset(H5S_t *space, const hssize_t *old_offset)
     HDassert(H5S_GET_SELECT_TYPE(space) == H5S_SEL_HYPERSLABS);
 
     /* Call the 'adjust' routine */
-    if(H5S_hyper_adjust_s(space, old_offset) < 0)
+    if(H5S__hyper_adjust_s(space, old_offset) < 0)
         HGOTO_ERROR(H5E_DATASPACE, H5E_CANTSET, FAIL, "can't adjust selection")
 
     /* Copy the selection offset over */
@@ -4907,12 +6992,11 @@ done:
  PURPOSE
     Create a new span and append to span list
  USAGE
-    herr_t H5S__hyper_append_span(prev_span, span_tree, low, high, down, next)
-        H5S_hyper_span_t **prev_span;    IN/OUT: Pointer to previous span in list
+    herr_t H5S__hyper_append_span(span_tree, ndims, low, high, down)
         H5S_hyper_span_info_t **span_tree;  IN/OUT: Pointer to span tree to append to
-        hsize_t low, high;         IN: Low and high bounds for new span node
+        unsigned ndims;                  IN: Number of dimension for span
+        hsize_t low, high;               IN: Low and high bounds for new span node
         H5S_hyper_span_info_t *down;     IN: Down span tree for new node
-        H5S_hyper_span_t *next;     IN: Next span for new node
  RETURNS
     Non-negative on success, negative on failure
  DESCRIPTION
@@ -4924,8 +7008,8 @@ done:
  REVISION LOG
 --------------------------------------------------------------------------*/
 static herr_t
-H5S__hyper_append_span(H5S_hyper_span_t **prev_span,
-    H5S_hyper_span_info_t **span_tree, hsize_t low, hsize_t high, H5S_hyper_span_info_t *down, H5S_hyper_span_t *next)
+H5S__hyper_append_span(H5S_hyper_span_info_t **span_tree, unsigned ndims,
+    hsize_t low, hsize_t high, H5S_hyper_span_info_t *down)
 {
     H5S_hyper_span_t *new_span = NULL;
     herr_t      ret_value = SUCCEED;       /* Return value */
@@ -4933,73 +7017,108 @@ H5S__hyper_append_span(H5S_hyper_span_t **prev_span,
     FUNC_ENTER_STATIC
 
     /* Sanity checks */
-    HDassert(prev_span);
     HDassert(span_tree);
 
     /* Check for adding first node to merged spans */
-    if(*prev_span == NULL) {
+    if(*span_tree == NULL) {
         /* Allocate new span node to append to list */
-        if(NULL == (new_span = H5S__hyper_new_span(low, high, down, next)))
+        if(NULL == (new_span = H5S__hyper_new_span(low, high, down, NULL)))
             HGOTO_ERROR(H5E_DATASPACE, H5E_CANTALLOC, FAIL, "can't allocate hyperslab span")
 
-        /* Make first node in span list */
-
-        /* Check that we haven't already allocated a span tree */
-        HDassert(*span_tree == NULL);
+        /* Make new span the first node in span list */
 
         /* Allocate a new span_info node */
-        if(NULL == (*span_tree = H5FL_CALLOC(H5S_hyper_span_info_t)))
+        if(NULL == (*span_tree = H5S__hyper_new_span_info(ndims)))
             HGOTO_ERROR(H5E_DATASPACE, H5E_CANTALLOC, FAIL, "can't allocate hyperslab span")
 
         /* Set the span tree's basic information */
         (*span_tree)->count = 1;
         (*span_tree)->head = new_span;
+        (*span_tree)->tail = new_span;
+
+        /* Set low & high bounds for new span tree */
+        (*span_tree)->low_bounds[0] = low;
+        (*span_tree)->high_bounds[0] = high;
+        if(down) {
+            /* Sanity check */
+            HDassert(ndims > 1);
 
-        /* Update previous merged span */
-        *prev_span = new_span;
+            H5MM_memcpy(&((*span_tree)->low_bounds[1]), down->low_bounds, sizeof(hsize_t) * (ndims - 1));
+            H5MM_memcpy(&((*span_tree)->high_bounds[1]), down->high_bounds, sizeof(hsize_t) * (ndims - 1));
+        } /* end if */
     } /* end if */
     /* Merge or append to existing merged spans list */
     else {
+        htri_t down_cmp = (-1);         /* Comparison value for down spans */
+
         /* Check if span can just extend the previous merged span */
-        if((((*prev_span)->high + 1) == low) &&
-                H5S__hyper_cmp_spans(down, (*prev_span)->down)==TRUE) {
+        if((((*span_tree)->tail->high + 1) == low) &&
+                (down_cmp = H5S__hyper_cmp_spans(down, (*span_tree)->tail->down))) {
             /* Extend previous merged span to include new high bound */
-            (*prev_span)->high = high;
-            (*prev_span)->nelem += (high - low) + 1;
+            (*span_tree)->tail->high = high;
+
+            /* Extend span tree's high bound in this dimension */
+            /* (No need to update lower dimensions, since this span shares them with previous span) */
+            (*span_tree)->high_bounds[0] = high;
         } /* end if */
         else {
-            /* Allocate new span node to append to list */
-            if(NULL == (new_span = H5S__hyper_new_span(low, high, down, next)))
-                HGOTO_ERROR(H5E_RESOURCE, H5E_NOSPACE, FAIL, "can't allocate hyperslab span")
+            H5S_hyper_span_info_t *new_down;    /* Down pointer for new span node */
+
+            /* Sanity check */
+            /* (If down_cmp was set to TRUE above, we won't be in this branch) */
+            HDassert(down_cmp != TRUE);
 
             /* Check if there is actually a down span */
-            if(new_span->down) {
+            if(down) {
                 /* Check if the down spans for the new span node are the same as the previous span node */
-                if(H5S__hyper_cmp_spans(new_span->down, (*prev_span)->down)) {
-                    /* Release the down span for the new node */
-                    H5S__hyper_free_span_info(new_span->down);
-
-                    /* Point the new node's down span at the previous node's down span */
-                    new_span->down = (*prev_span)->down;
+                /* (Uses the 'down span comparison' from earlier, if already computed) */
+                if(down_cmp < 0 && (down_cmp = H5S__hyper_cmp_spans(down, (*span_tree)->tail->down)))
+                    /* Share the previous span's down span tree */
+                    new_down = (*span_tree)->tail->down;
+                else
+                    new_down = down;
+            } /* end if */
+            else
+                new_down = NULL;
 
-                    /* Increment the reference count to the shared down span */
-                    new_span->down->count++;
+            /* Allocate new span node to append to list */
+            if(NULL == (new_span = H5S__hyper_new_span(low, high, new_down, NULL)))
+                HGOTO_ERROR(H5E_DATASPACE, H5E_CANTALLOC, FAIL, "can't allocate hyperslab span")
+
+            /* Update the high bounds for current dimension */
+            (*span_tree)->high_bounds[0] = high;
+
+            /* Update low & high bounds in lower dimensions, if there are any */
+            if(down) {
+                /* Sanity checks */
+                HDassert(ndims > 1);
+                HDassert(down_cmp >= 0);
+
+                /* Check if we are sharing down spans with a previous node */
+                /* (Only need to check for bounds changing if down spans aren't shared) */
+                if(down_cmp == FALSE) {
+                    unsigned u;     /* Local index variable */
+
+                    /* Loop over lower dimensions, checking & updating low & high bounds */
+                    for(u = 0; u < (ndims - 1); u++) {
+                        if(down->low_bounds[u] < (*span_tree)->low_bounds[u + 1])
+                            (*span_tree)->low_bounds[u + 1] = down->low_bounds[u];
+                        if(down->high_bounds[u] > (*span_tree)->high_bounds[u + 1])
+                            (*span_tree)->high_bounds[u + 1] = down->high_bounds[u];
+                    } /* end for */
                 } /* end if */
             } /* end if */
 
-            /* Indicate elements from previous span */
-            new_span->pstride = low - (*prev_span)->low;
-
             /* Append to end of merged spans list */
-            (*prev_span)->next = new_span;
-            *prev_span = new_span;
+            (*span_tree)->tail->next = new_span;
+            (*span_tree)->tail = new_span;
         } /* end else */
     } /* end else */
 
 done:
     if(ret_value < 0)
-        if(new_span && H5S__hyper_free_span(new_span) < 0)
-            HDONE_ERROR(H5E_DATASPACE, H5E_CANTFREE, FAIL, "failed to release new hyperslab span")
+        if(new_span)
+            H5S__hyper_free_span(new_span);
 
     FUNC_LEAVE_NOAPI(ret_value)
 } /* end H5S__hyper_append_span() */
@@ -5011,9 +7130,18 @@ done:
  PURPOSE
     Clip a new span tree against the current spans in the hyperslab selection
  USAGE
-    herr_t H5S__hyper_clip_spans(span_a, span_b, a_not_b, a_and_b, b_not_a)
+    herr_t H5S__hyper_clip_spans(span_a, span_b, selector, curr_dim, dim_size,
+                                span_a_b_bounds[4], all_clips_bound,
+                                a_not_b, a_and_b, b_not_a)
         H5S_hyper_span_t *a_spans;    IN: Span tree 'a' to clip with.
         H5S_hyper_span_t *b_spans;    IN: Span tree 'b' to clip with.
+        unsigned selector;            IN: The parameter deciding which output is needed
+                                          (only considering the last three bits ABC:
+                                           If A is set, then a_not_b is needed;
+                                           If B is set, then a_and_b is needed;
+                                           If C is set, then b_not_a is needed;
+                                           )
+        unsigned ndims;               IN: Number of dimensions of this span tree
         H5S_hyper_span_t **a_not_b;  OUT: Span tree of 'a' hyperslab spans which
                                             doesn't overlap with 'b' hyperslab
                                             spans.
@@ -5027,9 +7155,10 @@ done:
  DESCRIPTION
     Clip one span tree ('a') against another span tree ('b').  Creates span
     trees for the area defined by the 'a' span tree which does not overlap the
-    'b' span tree, the area defined by the overlap of the 'a' hyperslab span
-    tree and the 'b' span tree, and the area defined by the 'b' hyperslab span
-    tree which does not overlap the 'a' span tree.
+    'b' span tree ("a not b"), the area defined by the overlap of the 'a'
+    hyperslab span tree and the 'b' span tree ("a and b"), and the area defined
+    by the 'b' hyperslab span tree which does not overlap the 'a' span
+    tree ("b not a").
  GLOBAL VARIABLES
  COMMENTS, BUGS, ASSUMPTIONS
  EXAMPLES
@@ -5037,20 +7166,14 @@ done:
 --------------------------------------------------------------------------*/
 static herr_t
 H5S__hyper_clip_spans(H5S_hyper_span_info_t *a_spans, H5S_hyper_span_info_t *b_spans,
+    unsigned selector, unsigned ndims,
     H5S_hyper_span_info_t **a_not_b, H5S_hyper_span_info_t **a_and_b,
     H5S_hyper_span_info_t **b_not_a)
 {
-    H5S_hyper_span_t *span_a;   /* Pointer to a node in span tree 'a' */
-    H5S_hyper_span_t *span_b;   /* Pointer to a node in span tree 'b' */
-    H5S_hyper_span_t *tmp_span; /* Temporary pointer to new span */
-    H5S_hyper_span_t *last_a_not_b;   /* Pointer to previous node in span tree 'a_not_b' */
-    H5S_hyper_span_t *last_a_and_b;   /* Pointer to previous node in span tree 'a_and_b' */
-    H5S_hyper_span_t *last_b_not_a;   /* Pointer to previous node in span tree 'b_not_a' */
-    H5S_hyper_span_info_t *down_a_not_b; /* Temporary pointer to a_not_b span tree of down spans for overlapping nodes */
-    H5S_hyper_span_info_t *down_a_and_b; /* Temporary pointer to a_and_b span tree of down spans for overlapping nodes */
-    H5S_hyper_span_info_t *down_b_not_a; /* Temporary pointer to b_and_a span tree of down spans for overlapping nodes */
-    hbool_t recover_a, recover_b;         /* Flags to indicate when to recover temporary spans */
-    herr_t      ret_value = SUCCEED;     /* Return value */
+    hbool_t need_a_not_b;           /* Whether to generate a_not_b list */
+    hbool_t need_a_and_b;           /* Whether to generate a_and_b list */
+    hbool_t need_b_not_a;           /* Whether to generate b_not_a list */
+    herr_t ret_value = SUCCEED;     /* Return value */
 
     FUNC_ENTER_STATIC
 
@@ -5061,6 +7184,11 @@ H5S__hyper_clip_spans(H5S_hyper_span_info_t *a_spans, H5S_hyper_span_info_t *b_s
     HDassert(a_and_b);
     HDassert(b_not_a);
 
+    /* Set which list(s) to be generated, based on selector */
+    need_a_not_b = ((selector & H5S_HYPER_COMPUTE_A_NOT_B) != 0);
+    need_a_and_b = ((selector & H5S_HYPER_COMPUTE_A_AND_B) != 0);
+    need_b_not_a = ((selector & H5S_HYPER_COMPUTE_B_NOT_A) != 0);
+
     /* Check if both span trees are not defined */
     if(a_spans == NULL && b_spans == NULL) {
         *a_not_b = NULL;
@@ -5071,38 +7199,56 @@ H5S__hyper_clip_spans(H5S_hyper_span_info_t *a_spans, H5S_hyper_span_info_t *b_s
     else if(a_spans == NULL) {
         *a_not_b = NULL;
         *a_and_b = NULL;
-        if(NULL == (*b_not_a = H5S__hyper_copy_span(b_spans)))
-            HGOTO_ERROR(H5E_INTERNAL, H5E_CANTCOPY, FAIL, "can't copy hyperslab span tree")
+        if(need_b_not_a) {
+            if(NULL == (*b_not_a = H5S__hyper_copy_span(b_spans, ndims)))
+                HGOTO_ERROR(H5E_INTERNAL, H5E_CANTCOPY, FAIL, "can't copy hyperslab span tree")
+        } /* end if */
+        else
+            *b_not_a = NULL;
     } /* end if */
     /* If span 'b' is not defined, but 'a' is, copy 'a' and set the other return span trees to empty */
     else if(b_spans == NULL) {
-        if(NULL == (*a_not_b = H5S__hyper_copy_span(a_spans)) )
-            HGOTO_ERROR(H5E_INTERNAL, H5E_CANTCOPY, FAIL, "can't copy hyperslab span tree")
         *a_and_b = NULL;
         *b_not_a = NULL;
+        if(need_a_not_b) {
+            if(NULL == (*a_not_b = H5S__hyper_copy_span(a_spans, ndims)))
+                HGOTO_ERROR(H5E_INTERNAL, H5E_CANTCOPY, FAIL, "can't copy hyperslab span tree")
+        } /* end if */
+        else
+            *a_not_b = NULL;
     } /* end if */
     /* If span 'a' and 'b' are both defined, calculate the proper span trees */
     else {
         /* Check if both span trees completely overlap */
         if(H5S__hyper_cmp_spans(a_spans, b_spans)) {
             *a_not_b = NULL;
-            if(NULL == (*a_and_b = H5S__hyper_copy_span(a_spans)))
-                HGOTO_ERROR(H5E_INTERNAL, H5E_CANTCOPY, FAIL, "can't copy hyperslab span tree")
             *b_not_a = NULL;
+            if(need_a_and_b) {
+                if(NULL == (*a_and_b = H5S__hyper_copy_span(a_spans, ndims)))
+                    HGOTO_ERROR(H5E_INTERNAL, H5E_CANTCOPY, FAIL, "can't copy hyperslab span tree")
+            } /* end if */
+            else
+                *a_and_b = NULL;
         } /* end if */
         else {
+            H5S_hyper_span_t *span_a;       /* Pointer to a node in span tree 'a' */
+            H5S_hyper_span_t *span_b;       /* Pointer to a node in span tree 'b' */
+            hbool_t recover_a, recover_b;     /* Flags to indicate when to recover temporary spans */
+
             /* Get the pointers to the new and old span lists */
             span_a = a_spans->head;
             span_b = b_spans->head;
 
-            /* Reset the pointers to the previous spans */
-            last_a_not_b = last_a_and_b = last_b_not_a = NULL;
-
             /* No spans to recover yet */
             recover_a = recover_b = FALSE;
 
             /* Work through the list of spans in the new list */
             while(span_a != NULL && span_b != NULL) {
+                H5S_hyper_span_info_t *down_a_not_b; /* Temporary pointer to a_not_b span tree of down spans for overlapping nodes */
+                H5S_hyper_span_info_t *down_a_and_b; /* Temporary pointer to a_and_b span tree of down spans for overlapping nodes */
+                H5S_hyper_span_info_t *down_b_not_a; /* Temporary pointer to b_and_a span tree of down spans for overlapping nodes */
+                H5S_hyper_span_t *tmp_span; /* Temporary pointer to new span */
+
                 /* Check if span 'a' is completely before span 'b' */
                 /*    AAAAAAA                            */
                 /* <-----------------------------------> */
@@ -5111,11 +7257,12 @@ H5S__hyper_clip_spans(H5S_hyper_span_info_t *a_spans, H5S_hyper_span_info_t *b_s
                     /* Copy span 'a' and add to a_not_b list */
 
                     /* Merge/add span 'a' with/to a_not_b list */
-                    if(H5S__hyper_append_span(&last_a_not_b, a_not_b, span_a->low, span_a->high, span_a->down, NULL) < 0)
-                        HGOTO_ERROR(H5E_DATASPACE, H5E_CANTAPPEND, FAIL, "can't allocate hyperslab span")
+                    if(need_a_not_b)
+                        if(H5S__hyper_append_span(a_not_b, ndims, span_a->low, span_a->high, span_a->down) < 0)
+                            HGOTO_ERROR(H5E_DATASPACE, H5E_CANTAPPEND, FAIL, "can't allocate hyperslab span")
 
                     /* Advance span 'a', leave span 'b' */
-                    H5S__hyper_recover_span(&recover_a, &span_a, span_a->next);
+                    H5S_HYPER_ADVANCE_SPAN(recover_a, span_a, span_a->next);
                 } /* end if */
                 /* Check if span 'a' overlaps only the lower bound */
                 /*  of span 'b' , up to the upper bound of span 'b' */
@@ -5126,8 +7273,9 @@ H5S__hyper_clip_spans(H5S_hyper_span_info_t *a_spans, H5S_hyper_span_info_t *b_s
                     /* Split span 'a' into two parts at the low bound of span 'b' */
 
                     /* Merge/add lower part of span 'a' with/to a_not_b list */
-                    if(H5S__hyper_append_span(&last_a_not_b, a_not_b, span_a->low, span_b->low - 1, span_a->down, NULL) < 0)
-                        HGOTO_ERROR(H5E_DATASPACE, H5E_CANTAPPEND, FAIL, "can't allocate hyperslab span")
+                    if(need_a_not_b)
+                        if(H5S__hyper_append_span(a_not_b, ndims, span_a->low, span_b->low - 1, span_a->down) < 0)
+                            HGOTO_ERROR(H5E_DATASPACE, H5E_CANTAPPEND, FAIL, "can't allocate hyperslab span")
 
                     /* Check for overlaps between upper part of span 'a' and lower part of span 'b' */
 
@@ -5137,8 +7285,9 @@ H5S__hyper_clip_spans(H5S_hyper_span_info_t *a_spans, H5S_hyper_span_info_t *b_s
                     /* If there are no down spans, just add the overlapping area to the a_and_b list */
                     if(span_a->down == NULL) {
                         /* Merge/add overlapped part with/to a_and_b list */
-                        if(H5S__hyper_append_span(&last_a_and_b, a_and_b, span_b->low, span_a->high, NULL, NULL) < 0)
-                            HGOTO_ERROR(H5E_DATASPACE, H5E_CANTAPPEND, FAIL, "can't allocate hyperslab span")
+                        if(need_a_and_b)
+                            if(H5S__hyper_append_span(a_and_b, ndims, span_b->low, span_a->high, NULL) < 0)
+                                HGOTO_ERROR(H5E_DATASPACE, H5E_CANTAPPEND, FAIL, "can't allocate hyperslab span")
                     } /* end if */
                     /* If there are down spans, check for the overlap in them and add to each appropriate list */
                     else {
@@ -5148,14 +7297,20 @@ H5S__hyper_clip_spans(H5S_hyper_span_info_t *a_spans, H5S_hyper_span_info_t *b_s
                         down_b_not_a = NULL;
 
                         /* Check for overlaps in the 'down spans' of span 'a' & 'b' */
-                        if(H5S__hyper_clip_spans(span_a->down,span_b->down,&down_a_not_b,&down_a_and_b,&down_b_not_a)<0)
+                        /** Note: since the bound box of remaining dimensions
+                         *  has been updated in the following clip function (via
+                         *  all_clips_bounds), there's no need updating the bound box
+                         *  after each append call in the following codes */
+                        if(H5S__hyper_clip_spans(span_a->down, span_b->down, selector, ndims - 1, &down_a_not_b, &down_a_and_b, &down_b_not_a) < 0)
                             HGOTO_ERROR(H5E_DATASPACE, H5E_CANTCLIP, FAIL, "can't clip hyperslab information")
 
                         /* Check for additions to the a_not_b list */
                         if(down_a_not_b) {
+                            HDassert(need_a_not_b == TRUE);
+
                             /* Merge/add overlapped part with/to a_not_b list */
-                            if(H5S__hyper_append_span(&last_a_not_b,a_not_b,span_b->low,span_a->high,down_a_not_b,NULL)==FAIL)
-                                HGOTO_ERROR(H5E_RESOURCE, H5E_CANTAPPEND, FAIL, "can't allocate hyperslab span")
+                            if(H5S__hyper_append_span(a_not_b, ndims, span_b->low, span_a->high, down_a_not_b) < 0)
+                                HGOTO_ERROR(H5E_DATASPACE, H5E_CANTAPPEND, FAIL, "can't allocate hyperslab span")
 
                             /* Release the down span tree generated */
                             H5S__hyper_free_span_info(down_a_not_b);
@@ -5163,9 +7318,11 @@ H5S__hyper_clip_spans(H5S_hyper_span_info_t *a_spans, H5S_hyper_span_info_t *b_s
 
                         /* Check for additions to the a_and_b list */
                         if(down_a_and_b) {
+                            HDassert(need_a_and_b == TRUE);
+
                             /* Merge/add overlapped part with/to a_and_b list */
-                            if(H5S__hyper_append_span(&last_a_and_b,a_and_b,span_b->low,span_a->high,down_a_and_b,NULL)==FAIL)
-                                HGOTO_ERROR(H5E_RESOURCE, H5E_CANTAPPEND, FAIL, "can't allocate hyperslab span")
+                            if(H5S__hyper_append_span(a_and_b, ndims, span_b->low, span_a->high, down_a_and_b) < 0)
+                                HGOTO_ERROR(H5E_DATASPACE, H5E_CANTAPPEND, FAIL, "can't allocate hyperslab span")
 
                             /* Release the down span tree generated */
                             H5S__hyper_free_span_info(down_a_and_b);
@@ -5173,9 +7330,11 @@ H5S__hyper_clip_spans(H5S_hyper_span_info_t *a_spans, H5S_hyper_span_info_t *b_s
 
                         /* Check for additions to the b_not_a list */
                         if(down_b_not_a) {
+                            HDassert(need_b_not_a == TRUE);
+
                             /* Merge/add overlapped part with/to b_not_a list */
-                            if(H5S__hyper_append_span(&last_b_not_a,b_not_a,span_b->low,span_a->high,down_b_not_a,NULL)==FAIL)
-                                HGOTO_ERROR(H5E_RESOURCE, H5E_CANTAPPEND, FAIL, "can't allocate hyperslab span")
+                            if(H5S__hyper_append_span(b_not_a, ndims, span_b->low, span_a->high, down_b_not_a) < 0)
+                                HGOTO_ERROR(H5E_DATASPACE, H5E_CANTAPPEND, FAIL, "can't allocate hyperslab span")
 
                             /* Release the down span tree generated */
                             H5S__hyper_free_span_info(down_b_not_a);
@@ -5185,23 +7344,23 @@ H5S__hyper_clip_spans(H5S_hyper_span_info_t *a_spans, H5S_hyper_span_info_t *b_s
                     /* Split off upper part of span 'b' at upper span of span 'a' */
 
                     /* Check if there is actually an upper part of span 'b' to split off */
-                    if(span_a->high<span_b->high) {
+                    if(span_a->high < span_b->high) {
                         /* Allocate new span node for upper part of span 'b' */
                         if(NULL == (tmp_span = H5S__hyper_new_span(span_a->high + 1, span_b->high, span_b->down, span_b->next)))
-                            HGOTO_ERROR(H5E_RESOURCE, H5E_NOSPACE, FAIL, "can't allocate hyperslab span")
+                            HGOTO_ERROR(H5E_DATASPACE, H5E_NOSPACE, FAIL, "can't allocate hyperslab span")
 
                         /* Advance span 'a' */
-                        H5S__hyper_recover_span(&recover_a,&span_a,span_a->next);
+                        H5S_HYPER_ADVANCE_SPAN(recover_a, span_a, span_a->next);
 
                         /* Make upper part of span 'b' into new span 'b' */
-                        H5S__hyper_recover_span(&recover_b,&span_b,tmp_span);
+                        H5S_HYPER_ADVANCE_SPAN(recover_b, span_b, tmp_span);
                         recover_b = TRUE;
                     } /* end if */
                     /* No upper part of span 'b' to split */
                     else {
                         /* Advance both 'a' and 'b' */
-                        H5S__hyper_recover_span(&recover_a,&span_a,span_a->next);
-                        H5S__hyper_recover_span(&recover_b,&span_b,span_b->next);
+                        H5S_HYPER_ADVANCE_SPAN(recover_a, span_a, span_a->next);
+                        H5S_HYPER_ADVANCE_SPAN(recover_b, span_b, span_b->next);
                     } /* end else */
                 } /* end if */
                 /* Check if span 'a' overlaps the lower & upper bound */
@@ -5213,8 +7372,9 @@ H5S__hyper_clip_spans(H5S_hyper_span_info_t *a_spans, H5S_hyper_span_info_t *b_s
                     /* Split off lower part of span 'a' at lower span of span 'b' */
 
                     /* Merge/add lower part of span 'a' with/to a_not_b list */
-                    if(H5S__hyper_append_span(&last_a_not_b,a_not_b,span_a->low,span_b->low-1,span_a->down,NULL)==FAIL)
-                        HGOTO_ERROR(H5E_RESOURCE, H5E_CANTAPPEND, FAIL, "can't allocate hyperslab span")
+                    if(need_a_not_b)
+                        if(H5S__hyper_append_span(a_not_b, ndims, span_a->low, span_b->low - 1, span_a->down) < 0)
+                            HGOTO_ERROR(H5E_DATASPACE, H5E_CANTAPPEND, FAIL, "can't allocate hyperslab span")
 
                     /* Check for overlaps between middle part of span 'a' and span 'b' */
 
@@ -5224,8 +7384,9 @@ H5S__hyper_clip_spans(H5S_hyper_span_info_t *a_spans, H5S_hyper_span_info_t *b_s
                     /* If there are no down spans, just add the overlapping area to the a_and_b list */
                     if(span_a->down == NULL) {
                         /* Merge/add overlapped part with/to a_and_b list */
-                        if(H5S__hyper_append_span(&last_a_and_b,a_and_b,span_b->low,span_b->high,NULL,NULL)==FAIL)
-                            HGOTO_ERROR(H5E_RESOURCE, H5E_CANTAPPEND, FAIL, "can't allocate hyperslab span")
+                        if(need_a_and_b)
+                            if(H5S__hyper_append_span(a_and_b, ndims, span_b->low, span_b->high, NULL) < 0)
+                                HGOTO_ERROR(H5E_DATASPACE, H5E_CANTAPPEND, FAIL, "can't allocate hyperslab span")
                     } /* end if */
                     /* If there are down spans, check for the overlap in them and add to each appropriate list */
                     else {
@@ -5235,14 +7396,16 @@ H5S__hyper_clip_spans(H5S_hyper_span_info_t *a_spans, H5S_hyper_span_info_t *b_s
                         down_b_not_a = NULL;
 
                         /* Check for overlaps in the 'down spans' of span 'a' & 'b' */
-                        if(H5S__hyper_clip_spans(span_a->down,span_b->down,&down_a_not_b,&down_a_and_b,&down_b_not_a)<0)
+                        if(H5S__hyper_clip_spans(span_a->down, span_b->down, selector, ndims - 1, &down_a_not_b, &down_a_and_b, &down_b_not_a) < 0)
                             HGOTO_ERROR(H5E_DATASPACE, H5E_CANTCLIP, FAIL, "can't clip hyperslab information")
 
                         /* Check for additions to the a_not_b list */
                         if(down_a_not_b) {
+                            HDassert(need_a_not_b == TRUE);
+
                             /* Merge/add overlapped part with/to a_not_b list */
-                            if(H5S__hyper_append_span(&last_a_not_b,a_not_b,span_b->low,span_b->high,down_a_not_b,NULL)==FAIL)
-                                HGOTO_ERROR(H5E_RESOURCE, H5E_CANTAPPEND, FAIL, "can't allocate hyperslab span")
+                            if(H5S__hyper_append_span(a_not_b, ndims, span_b->low, span_b->high, down_a_not_b) < 0)
+                                HGOTO_ERROR(H5E_DATASPACE, H5E_CANTAPPEND, FAIL, "can't allocate hyperslab span")
 
                             /* Release the down span tree generated */
                             H5S__hyper_free_span_info(down_a_not_b);
@@ -5250,9 +7413,11 @@ H5S__hyper_clip_spans(H5S_hyper_span_info_t *a_spans, H5S_hyper_span_info_t *b_s
 
                         /* Check for additions to the a_and_b list */
                         if(down_a_and_b) {
+                            HDassert(need_a_and_b == TRUE);
+
                             /* Merge/add overlapped part with/to a_and_b list */
-                            if(H5S__hyper_append_span(&last_a_and_b,a_and_b,span_b->low,span_b->high,down_a_and_b,NULL)==FAIL)
-                                HGOTO_ERROR(H5E_RESOURCE, H5E_CANTAPPEND, FAIL, "can't allocate hyperslab span")
+                            if(H5S__hyper_append_span(a_and_b, ndims, span_b->low, span_b->high, down_a_and_b) < 0)
+                                HGOTO_ERROR(H5E_DATASPACE, H5E_CANTAPPEND, FAIL, "can't allocate hyperslab span")
 
                             /* Release the down span tree generated */
                             H5S__hyper_free_span_info(down_a_and_b);
@@ -5260,9 +7425,11 @@ H5S__hyper_clip_spans(H5S_hyper_span_info_t *a_spans, H5S_hyper_span_info_t *b_s
 
                         /* Check for additions to the b_not_a list */
                         if(down_b_not_a) {
+                            HDassert(need_b_not_a == TRUE);
+
                             /* Merge/add overlapped part with/to b_not_a list */
-                            if(H5S__hyper_append_span(&last_b_not_a,b_not_a,span_b->low,span_b->high,down_b_not_a,NULL)==FAIL)
-                                HGOTO_ERROR(H5E_RESOURCE, H5E_CANTAPPEND, FAIL, "can't allocate hyperslab span")
+                            if(H5S__hyper_append_span(b_not_a, ndims, span_b->low, span_b->high, down_b_not_a) < 0)
+                                HGOTO_ERROR(H5E_DATASPACE, H5E_CANTAPPEND, FAIL, "can't allocate hyperslab span")
 
                             /* Release the down span tree generated */
                             H5S__hyper_free_span_info(down_b_not_a);
@@ -5276,11 +7443,11 @@ H5S__hyper_clip_spans(H5S_hyper_span_info_t *a_spans, H5S_hyper_span_info_t *b_s
                         HGOTO_ERROR(H5E_DATASPACE, H5E_NOSPACE, FAIL, "can't allocate hyperslab span")
 
                     /* Make upper part of span 'a' the new span 'a' */
-                    H5S__hyper_recover_span(&recover_a,&span_a,tmp_span);
+                    H5S_HYPER_ADVANCE_SPAN(recover_a, span_a, tmp_span);
                     recover_a = TRUE;
 
                     /* Advance span 'b' */
-                    H5S__hyper_recover_span(&recover_b,&span_b,span_b->next);
+                    H5S_HYPER_ADVANCE_SPAN(recover_b, span_b, span_b->next);
                 } /* end if */
                 /* Check if span 'a' is entirely within span 'b' */
                 /*                AAAAA                  */
@@ -5292,8 +7459,9 @@ H5S__hyper_clip_spans(H5S_hyper_span_info_t *a_spans, H5S_hyper_span_info_t *b_s
                     /* Check if there is actually a lower part of span 'b' to split off */
                     if(span_a->low > span_b->low) {
                         /* Merge/add lower part of span 'b' with/to b_not_a list */
-                        if(H5S__hyper_append_span(&last_b_not_a,b_not_a,span_b->low,span_a->low-1,span_b->down,NULL)==FAIL)
-                            HGOTO_ERROR(H5E_RESOURCE, H5E_CANTAPPEND, FAIL, "can't allocate hyperslab span")
+                        if(need_b_not_a)
+                            if(H5S__hyper_append_span(b_not_a, ndims, span_b->low, span_a->low - 1, span_b->down) < 0)
+                                HGOTO_ERROR(H5E_DATASPACE, H5E_CANTAPPEND, FAIL, "can't allocate hyperslab span")
                     } /* end if */
                     else {
                         /* Keep going, nothing to split off */
@@ -5307,8 +7475,9 @@ H5S__hyper_clip_spans(H5S_hyper_span_info_t *a_spans, H5S_hyper_span_info_t *b_s
                     /* If there are no down spans, just add the overlapping area to the a_and_b list */
                     if(span_a->down == NULL) {
                         /* Merge/add overlapped part with/to a_and_b list */
-                        if(H5S__hyper_append_span(&last_a_and_b,a_and_b,span_a->low,span_a->high,NULL,NULL)==FAIL)
-                            HGOTO_ERROR(H5E_RESOURCE, H5E_CANTAPPEND, FAIL, "can't allocate hyperslab span")
+                        if(need_a_and_b)
+                            if(H5S__hyper_append_span(a_and_b, ndims, span_a->low, span_a->high, NULL) < 0)
+                                HGOTO_ERROR(H5E_DATASPACE, H5E_CANTAPPEND, FAIL, "can't allocate hyperslab span")
                     } /* end if */
                     /* If there are down spans, check for the overlap in them and add to each appropriate list */
                     else {
@@ -5318,34 +7487,40 @@ H5S__hyper_clip_spans(H5S_hyper_span_info_t *a_spans, H5S_hyper_span_info_t *b_s
                         down_b_not_a = NULL;
 
                         /* Check for overlaps in the 'down spans' of span 'a' & 'b' */
-                        if(H5S__hyper_clip_spans(span_a->down,span_b->down,&down_a_not_b,&down_a_and_b,&down_b_not_a)<0)
+                        if(H5S__hyper_clip_spans(span_a->down, span_b->down, selector, ndims - 1, &down_a_not_b, &down_a_and_b, &down_b_not_a) < 0)
                             HGOTO_ERROR(H5E_DATASPACE, H5E_CANTCLIP, FAIL, "can't clip hyperslab information")
 
                         /* Check for additions to the a_not_b list */
                         if(down_a_not_b) {
+                            HDassert(need_a_not_b == TRUE);
+
                             /* Merge/add overlapped part with/to a_not_b list */
-                            if(H5S__hyper_append_span(&last_a_not_b,a_not_b,span_a->low,span_a->high,down_a_not_b,NULL)==FAIL)
-                                HGOTO_ERROR(H5E_RESOURCE, H5E_CANTAPPEND, FAIL, "can't allocate hyperslab span")
+                            if(H5S__hyper_append_span(a_not_b, ndims, span_a->low, span_a->high, down_a_not_b) < 0)
+                                HGOTO_ERROR(H5E_DATASPACE, H5E_CANTAPPEND, FAIL, "can't allocate hyperslab span")
 
                             /* Release the down span tree generated */
                             H5S__hyper_free_span_info(down_a_not_b);
                         } /* end if */
 
                         /* Check for additions to the a_and_b list */
-                        if(down_a_and_b!=NULL) {
+                        if(down_a_and_b) {
+                            HDassert(need_a_and_b == TRUE);
+
                             /* Merge/add overlapped part with/to a_and_b list */
-                            if(H5S__hyper_append_span(&last_a_and_b,a_and_b,span_a->low,span_a->high,down_a_and_b,NULL)==FAIL)
-                                HGOTO_ERROR(H5E_RESOURCE, H5E_CANTAPPEND, FAIL, "can't allocate hyperslab span")
+                            if(H5S__hyper_append_span(a_and_b, ndims, span_a->low, span_a->high, down_a_and_b) < 0)
+                                HGOTO_ERROR(H5E_DATASPACE, H5E_CANTAPPEND, FAIL, "can't allocate hyperslab span")
 
                             /* Release the down span tree generated */
                             H5S__hyper_free_span_info(down_a_and_b);
                         } /* end if */
 
                         /* Check for additions to the b_not_a list */
-                        if(down_b_not_a!=NULL) {
+                        if(down_b_not_a) {
+                            HDassert(need_b_not_a == TRUE);
+
                             /* Merge/add overlapped part with/to b_not_a list */
-                            if(H5S__hyper_append_span(&last_b_not_a,b_not_a,span_a->low,span_a->high,down_b_not_a,NULL)==FAIL)
-                                HGOTO_ERROR(H5E_RESOURCE, H5E_CANTAPPEND, FAIL, "can't allocate hyperslab span")
+                            if(H5S__hyper_append_span(b_not_a, ndims, span_a->low, span_a->high, down_b_not_a) < 0)
+                                HGOTO_ERROR(H5E_DATASPACE, H5E_CANTAPPEND, FAIL, "can't allocate hyperslab span")
 
                             /* Release the down span tree generated */
                             H5S__hyper_free_span_info(down_b_not_a);
@@ -5353,24 +7528,24 @@ H5S__hyper_clip_spans(H5S_hyper_span_info_t *a_spans, H5S_hyper_span_info_t *b_s
                     } /* end else */
 
                     /* Check if there is actually an upper part of span 'b' to split off */
-                    if(span_a->high<span_b->high) {
+                    if(span_a->high < span_b->high) {
                         /* Split off upper part of span 'b' at upper span of span 'a' */
 
                         /* Allocate new span node for upper part of spans 'a' */
                         if(NULL == (tmp_span = H5S__hyper_new_span(span_a->high + 1, span_b->high, span_b->down, span_b->next)))
-                            HGOTO_ERROR(H5E_RESOURCE, H5E_NOSPACE, FAIL, "can't allocate hyperslab span")
+                            HGOTO_ERROR(H5E_DATASPACE, H5E_CANTALLOC, FAIL, "can't allocate hyperslab span")
 
                         /* And advance span 'a' */
-                        H5S__hyper_recover_span(&recover_a,&span_a,span_a->next);
+                        H5S_HYPER_ADVANCE_SPAN(recover_a, span_a, span_a->next);
 
                         /* Make upper part of span 'b' the new span 'b' */
-                        H5S__hyper_recover_span(&recover_b,&span_b,tmp_span);
-                        recover_b=1;
+                        H5S_HYPER_ADVANCE_SPAN(recover_b, span_b, tmp_span);
+                        recover_b = TRUE;
                     } /* end if */
                     else {
                         /* Advance both span 'a' & span 'b' */
-                        H5S__hyper_recover_span(&recover_a,&span_a,span_a->next);
-                        H5S__hyper_recover_span(&recover_b,&span_b,span_b->next);
+                        H5S_HYPER_ADVANCE_SPAN(recover_a, span_a, span_a->next);
+                        H5S_HYPER_ADVANCE_SPAN(recover_b, span_b, span_b->next);
                     } /* end else */
                 } /* end if */
                 /* Check if span 'a' overlaps only the upper bound */
@@ -5378,14 +7553,15 @@ H5S__hyper_clip_spans(H5S_hyper_span_info_t *a_spans, H5S_hyper_span_info_t *b_s
                 /*                AAAAAAAAAA             */
                 /* <-----------------------------------> */
                 /*             BBBBBBBBBB                */
-                else if((span_a->low>=span_b->low && span_a->low<=span_b->high) && span_a->high>span_b->high) {
+                else if((span_a->low >= span_b->low && span_a->low <= span_b->high) && span_a->high > span_b->high) {
                     /* Check if there is actually a lower part of span 'b' to split off */
-                    if(span_a->low>span_b->low) {
+                    if(span_a->low > span_b->low) {
                         /* Split off lower part of span 'b' at lower span of span 'a' */
 
                         /* Merge/add lower part of span 'b' with/to b_not_a list */
-                        if(H5S__hyper_append_span(&last_b_not_a,b_not_a,span_b->low,span_a->low-1,span_b->down,NULL)==FAIL)
-                            HGOTO_ERROR(H5E_RESOURCE, H5E_CANTAPPEND, FAIL, "can't allocate hyperslab span")
+                        if(need_b_not_a)
+                            if(H5S__hyper_append_span(b_not_a, ndims, span_b->low, span_a->low - 1, span_b->down) < 0)
+                                HGOTO_ERROR(H5E_DATASPACE, H5E_CANTAPPEND, FAIL, "can't allocate hyperslab span")
                     } /* end if */
                     else {
                         /* Keep going, nothing to split off */
@@ -5399,8 +7575,9 @@ H5S__hyper_clip_spans(H5S_hyper_span_info_t *a_spans, H5S_hyper_span_info_t *b_s
                     /* If there are no down spans, just add the overlapping area to the a_and_b list */
                     if(span_a->down == NULL) {
                         /* Merge/add overlapped part with/to a_and_b list */
-                        if(H5S__hyper_append_span(&last_a_and_b,a_and_b,span_a->low,span_b->high,NULL,NULL)==FAIL)
-                            HGOTO_ERROR(H5E_RESOURCE, H5E_CANTAPPEND, FAIL, "can't allocate hyperslab span")
+                        if(need_a_and_b)
+                            if(H5S__hyper_append_span(a_and_b, ndims, span_a->low, span_b->high, NULL) < 0)
+                                HGOTO_ERROR(H5E_DATASPACE, H5E_CANTAPPEND, FAIL, "can't allocate hyperslab span")
                     } /* end if */
                     /* If there are down spans, check for the overlap in them and add to each appropriate list */
                     else {
@@ -5410,24 +7587,28 @@ H5S__hyper_clip_spans(H5S_hyper_span_info_t *a_spans, H5S_hyper_span_info_t *b_s
                         down_b_not_a = NULL;
 
                         /* Check for overlaps in the 'down spans' of span 'a' & 'b' */
-                        if(H5S__hyper_clip_spans(span_a->down,span_b->down,&down_a_not_b,&down_a_and_b,&down_b_not_a)<0)
+                        if(H5S__hyper_clip_spans(span_a->down, span_b->down, selector, ndims - 1, &down_a_not_b, &down_a_and_b, &down_b_not_a) < 0)
                             HGOTO_ERROR(H5E_DATASPACE, H5E_CANTCLIP, FAIL, "can't clip hyperslab information")
 
                         /* Check for additions to the a_not_b list */
                         if(down_a_not_b) {
+                            HDassert(need_a_not_b == TRUE);
+
                             /* Merge/add overlapped part with/to a_not_b list */
-                            if(H5S__hyper_append_span(&last_a_not_b,a_not_b,span_a->low,span_b->high,down_a_not_b,NULL)==FAIL)
-                                HGOTO_ERROR(H5E_RESOURCE, H5E_CANTAPPEND, FAIL, "can't allocate hyperslab span")
+                            if(H5S__hyper_append_span(a_not_b, ndims, span_a->low, span_b->high, down_a_not_b) < 0)
+                                HGOTO_ERROR(H5E_DATASPACE, H5E_CANTAPPEND, FAIL, "can't allocate hyperslab span")
 
                             /* Release the down span tree generated */
                             H5S__hyper_free_span_info(down_a_not_b);
                         } /* end if */
 
                         /* Check for additions to the a_and_b list */
-                        if(down_a_and_b!=NULL) {
+                        if(down_a_and_b) {
+                            HDassert(need_a_and_b == TRUE);
+
                             /* Merge/add overlapped part with/to a_and_b list */
-                            if(H5S__hyper_append_span(&last_a_and_b,a_and_b,span_a->low,span_b->high,down_a_and_b,NULL)==FAIL)
-                                HGOTO_ERROR(H5E_RESOURCE, H5E_CANTAPPEND, FAIL, "can't allocate hyperslab span")
+                            if(H5S__hyper_append_span(a_and_b, ndims, span_a->low, span_b->high, down_a_and_b) < 0)
+                                HGOTO_ERROR(H5E_DATASPACE, H5E_CANTAPPEND, FAIL, "can't allocate hyperslab span")
 
                             /* Release the down span tree generated */
                             H5S__hyper_free_span_info(down_a_and_b);
@@ -5435,9 +7616,11 @@ H5S__hyper_clip_spans(H5S_hyper_span_info_t *a_spans, H5S_hyper_span_info_t *b_s
 
                         /* Check for additions to the b_not_a list */
                         if(down_b_not_a) {
+                            HDassert(need_b_not_a == TRUE);
+
                             /* Merge/add overlapped part with/to b_not_a list */
-                            if(H5S__hyper_append_span(&last_b_not_a,b_not_a,span_a->low,span_b->high,down_b_not_a,NULL)==FAIL)
-                                HGOTO_ERROR(H5E_RESOURCE, H5E_CANTAPPEND, FAIL, "can't allocate hyperslab span")
+                            if(H5S__hyper_append_span(b_not_a, ndims, span_a->low, span_b->high, down_b_not_a) < 0)
+                                HGOTO_ERROR(H5E_DATASPACE, H5E_CANTAPPEND, FAIL, "can't allocate hyperslab span")
 
                             /* Release the down span tree generated */
                             H5S__hyper_free_span_info(down_b_not_a);
@@ -5448,14 +7631,14 @@ H5S__hyper_clip_spans(H5S_hyper_span_info_t *a_spans, H5S_hyper_span_info_t *b_s
 
                     /* Allocate new span node for upper part of span 'a' */
                     if(NULL == (tmp_span = H5S__hyper_new_span(span_b->high + 1, span_a->high, span_a->down, span_a->next)))
-                        HGOTO_ERROR(H5E_RESOURCE, H5E_NOSPACE, FAIL, "can't allocate hyperslab span")
+                        HGOTO_ERROR(H5E_DATASPACE, H5E_CANTALLOC, FAIL, "can't allocate hyperslab span")
 
                     /* Make upper part of span 'a' into new span 'a' */
-                    H5S__hyper_recover_span(&recover_a,&span_a,tmp_span);
-                    recover_a=1;
+                    H5S_HYPER_ADVANCE_SPAN(recover_a, span_a, tmp_span);
+                    recover_a = TRUE;
 
                     /* Advance span 'b' */
-                    H5S__hyper_recover_span(&recover_b,&span_b,span_b->next);
+                    H5S_HYPER_ADVANCE_SPAN(recover_b, span_b, span_b->next);
                 } /* end if */
                 /* span 'a' must be entirely above span 'b' */
                 /*                         AAAAA         */
@@ -5465,40 +7648,70 @@ H5S__hyper_clip_spans(H5S_hyper_span_info_t *a_spans, H5S_hyper_span_info_t *b_s
                     /* Copy span 'b' and add to b_not_a list */
 
                     /* Merge/add span 'b' with/to b_not_a list */
-                    if(H5S__hyper_append_span(&last_b_not_a,b_not_a,span_b->low,span_b->high,span_b->down,NULL)==FAIL)
-                        HGOTO_ERROR(H5E_RESOURCE, H5E_CANTAPPEND, FAIL, "can't allocate hyperslab span")
+                    if(need_b_not_a)
+                        if(H5S__hyper_append_span(b_not_a, ndims, span_b->low, span_b->high, span_b->down) < 0)
+                            HGOTO_ERROR(H5E_DATASPACE, H5E_CANTAPPEND, FAIL, "can't allocate hyperslab span")
 
                     /* Advance span 'b', leave span 'a' */
-                    H5S__hyper_recover_span(&recover_b,&span_b,span_b->next);
+                    H5S_HYPER_ADVANCE_SPAN(recover_b, span_b, span_b->next);
                 } /* end else */
             } /* end while */
 
             /* Clean up 'a' spans which haven't been covered yet */
             if(span_a != NULL && span_b == NULL) {
-                while(span_a != NULL) {
-                    /* Copy span 'a' and add to a_not_b list */
-
-                    /* Merge/add span 'a' with/to a_not_b list */
-                    if(H5S__hyper_append_span(&last_a_not_b,a_not_b,span_a->low,span_a->high,span_a->down,NULL)==FAIL)
-                        HGOTO_ERROR(H5E_RESOURCE, H5E_CANTAPPEND, FAIL, "can't allocate hyperslab span")
+                /* Check if need to merge/add 'a' spans with/to a_not_b list */
+                if(need_a_not_b) {
+                    /* (This loop, and the similar one below for 'b' spans,
+                     *  could be replaced with an optimized routine that quickly
+                     *  appended the remaining spans to the 'not' list, but
+                     *  until it looks like it's taking a lot of time for an
+                     *  important use case, it's been left generic, and similar
+                     *  to other code above. -QAK, 2019/02/01)
+                     */
+                    while(span_a != NULL) {
+                        /* Copy span 'a' and add to a_not_b list */
+                        if(H5S__hyper_append_span(a_not_b, ndims, span_a->low, span_a->high, span_a->down) < 0)
+                            HGOTO_ERROR(H5E_DATASPACE, H5E_CANTAPPEND, FAIL, "can't allocate hyperslab span")
 
-                    /* Advance to the next 'a' span */
-                    H5S__hyper_recover_span(&recover_a,&span_a,span_a->next);
-                } /* end while */
+                        /* Advance to the next 'a' span */
+                        H5S_HYPER_ADVANCE_SPAN(recover_a, span_a, span_a->next);
+                    } /* end while */
+                } /* end if */
+                else {
+                    /* Free the span, if it's generated */
+                    if(recover_a)
+                        H5S__hyper_free_span(span_a);
+                } /* end else */
             } /* end if */
             /* Clean up 'b' spans which haven't been covered yet */
             else if(span_a == NULL && span_b != NULL) {
-                while(span_b != NULL) {
-                    /* Copy span 'b' and add to b_not_a list */
-
-                    /* Merge/add span 'b' with/to b_not_a list */
-                    if(H5S__hyper_append_span(&last_b_not_a,b_not_a,span_b->low,span_b->high,span_b->down,NULL)==FAIL)
-                        HGOTO_ERROR(H5E_RESOURCE, H5E_CANTAPPEND, FAIL, "can't allocate hyperslab span")
+                /* Check if need to merge/add 'b' spans with/to b_not_a list */
+                if(need_b_not_a) {
+                    /* (This loop, and the similar one above for 'a' spans,
+                     *  could be replaced with an optimized routine that quickly
+                     *  appended the remaining spans to the 'not' list, but
+                     *  until it looks like it's taking a lot of time for an
+                     *  important use case, it's been left generic, and similar
+                     *  to other code above. -QAK, 2019/02/01)
+                     */
+                    while(span_b != NULL) {
+                        /* Copy span 'b' and add to b_not_a list */
+                        if(H5S__hyper_append_span(b_not_a, ndims, span_b->low, span_b->high, span_b->down) < 0)
+                            HGOTO_ERROR(H5E_DATASPACE, H5E_CANTAPPEND, FAIL, "can't allocate hyperslab span")
 
-                    /* Advance to the next 'b' span */
-                    H5S__hyper_recover_span(&recover_b,&span_b,span_b->next);
-                } /* end while */
+                        /* Advance to the next 'b' span */
+                        H5S_HYPER_ADVANCE_SPAN(recover_b, span_b, span_b->next);
+                    } /* end while */
+                } /* end if */
+                else {
+                    /* Free the span, if it's generated */
+                    if(recover_b)
+                        H5S__hyper_free_span(span_b);
+                } /* end else */
             } /* end if */
+            else
+                /* Sanity check */
+                HDassert(span_a == NULL && span_b == NULL);
         } /* end else */
     } /* end else */
 
@@ -5518,6 +7731,7 @@ done:
                                                 together
         H5S_hyper_span_info_t *b_spans; IN: Second hyperslab spans to merge
                                                 together
+        unsigned ndims;                 IN: Number of dimensions of this span tree
  RETURNS
     Pointer to span tree containing the merged spans on success, NULL on failure
  DESCRIPTION
@@ -5525,19 +7739,15 @@ done:
     the merged set.
  GLOBAL VARIABLES
  COMMENTS, BUGS, ASSUMPTIONS
+    Handles merging span trees that overlap.
  EXAMPLES
  REVISION LOG
 --------------------------------------------------------------------------*/
 static H5S_hyper_span_info_t *
-H5S__hyper_merge_spans_helper(H5S_hyper_span_info_t *a_spans, H5S_hyper_span_info_t *b_spans)
+H5S__hyper_merge_spans_helper(H5S_hyper_span_info_t *a_spans, H5S_hyper_span_info_t *b_spans,
+    unsigned ndims)
 {
     H5S_hyper_span_info_t *merged_spans = NULL; /* Pointer to the merged span tree */
-    H5S_hyper_span_info_t *tmp_spans;   /* Pointer to temporary new span tree */
-    H5S_hyper_span_t *tmp_span;         /* Pointer to temporary new span */
-    H5S_hyper_span_t *span_a;           /* Pointer to current span 'a' working on */
-    H5S_hyper_span_t *span_b;           /* Pointer to current span 'b' working on */
-    H5S_hyper_span_t *prev_span_merge;  /* Pointer to previous merged span */
-    hbool_t recover_a, recover_b;         /* Flags to indicate when to recover temporary spans */
     H5S_hyper_span_info_t *ret_value = NULL;    /* Return value */
 
     FUNC_ENTER_STATIC
@@ -5551,34 +7761,38 @@ H5S__hyper_merge_spans_helper(H5S_hyper_span_info_t *a_spans, H5S_hyper_span_inf
             merged_spans = NULL;
         else {
             /* Copy one of the span trees to return */
-            if(NULL == (merged_spans = H5S__hyper_copy_span(a_spans)))
+            if(NULL == (merged_spans = H5S__hyper_copy_span(a_spans, ndims)))
                 HGOTO_ERROR(H5E_INTERNAL, H5E_CANTCOPY, NULL, "can't copy hyperslab span tree")
         } /* end else */
     } /* end if */
     else {
+        H5S_hyper_span_t *span_a;           /* Pointer to current span 'a' working on */
+        H5S_hyper_span_t *span_b;           /* Pointer to current span 'b' working on */
+        hbool_t recover_a, recover_b;       /* Flags to indicate when to recover temporary spans */
+
         /* Get the pointers to the 'a' and 'b' span lists */
         span_a = a_spans->head;
         span_b = b_spans->head;
 
-        /* Set the pointer to the previous spans */
-        prev_span_merge = NULL;
-
         /* No spans to recover yet */
         recover_a = recover_b = FALSE;
 
         /* Work through the list of spans in the new list */
         while(span_a != NULL && span_b != NULL) {
+            H5S_hyper_span_info_t *tmp_spans;   /* Pointer to temporary new span tree */
+            H5S_hyper_span_t *tmp_span;         /* Pointer to temporary new span */
+
             /* Check if the 'a' span is completely before 'b' span */
             /*    AAAAAAA                            */
             /* <-----------------------------------> */
             /*             BBBBBBBBBB                */
             if(span_a->high < span_b->low) {
                 /* Merge/add span 'a' with/to the merged spans */
-                if(H5S__hyper_append_span(&prev_span_merge,&merged_spans,span_a->low,span_a->high,span_a->down,NULL)==FAIL)
+                if(H5S__hyper_append_span(&merged_spans, ndims, span_a->low, span_a->high, span_a->down) < 0)
                     HGOTO_ERROR(H5E_DATASPACE, H5E_CANTAPPEND, NULL, "can't allocate hyperslab span")
 
                 /* Advance span 'a' */
-                H5S__hyper_recover_span(&recover_a,&span_a,span_a->next);
+                H5S_HYPER_ADVANCE_SPAN(recover_a, span_a, span_a->next);
             } /* end if */
             /* Check if span 'a' overlaps only the lower bound */
             /*  of span 'b', up to the upper bound of span 'b' */
@@ -5589,19 +7803,19 @@ H5S__hyper_merge_spans_helper(H5S_hyper_span_info_t *a_spans, H5S_hyper_span_inf
                 /* Check if span 'a' and span 'b' down spans are equal */
                 if(H5S__hyper_cmp_spans(span_a->down, span_b->down)) {
                     /* Merge/add copy of span 'a' with/to merged spans */
-                    if(H5S__hyper_append_span(&prev_span_merge,&merged_spans,span_a->low,span_a->high,span_a->down,NULL)==FAIL)
+                    if(H5S__hyper_append_span(&merged_spans, ndims, span_a->low, span_a->high, span_a->down) < 0)
                         HGOTO_ERROR(H5E_DATASPACE, H5E_CANTAPPEND, NULL, "can't allocate hyperslab span")
                 } /* end if */
                 else {
                     /* Merge/add lower part of span 'a' with/to merged spans */
-                    if(H5S__hyper_append_span(&prev_span_merge,&merged_spans,span_a->low,span_b->low-1,span_a->down,NULL)==FAIL)
+                    if(H5S__hyper_append_span(&merged_spans, ndims, span_a->low, span_b->low - 1, span_a->down) < 0)
                         HGOTO_ERROR(H5E_DATASPACE, H5E_CANTAPPEND, NULL, "can't allocate hyperslab span")
 
                     /* Get merged span tree for overlapped section */
-                    tmp_spans = H5S__hyper_merge_spans_helper(span_a->down,span_b->down);
+                    tmp_spans = H5S__hyper_merge_spans_helper(span_a->down, span_b->down, ndims - 1);
 
                     /* Merge/add overlapped section to merged spans */
-                    if(H5S__hyper_append_span(&prev_span_merge,&merged_spans,span_b->low,span_a->high,tmp_spans,NULL)==FAIL)
+                    if(H5S__hyper_append_span(&merged_spans, ndims, span_b->low, span_a->high, tmp_spans) < 0)
                         HGOTO_ERROR(H5E_DATASPACE, H5E_CANTAPPEND, NULL, "can't allocate hyperslab span")
 
                     /* Release merged span tree for overlapped section */
@@ -5613,20 +7827,20 @@ H5S__hyper_merge_spans_helper(H5S_hyper_span_info_t *a_spans, H5S_hyper_span_inf
                     /* Copy upper part of span 'b' as new span 'b' */
 
                     /* Allocate new span node to append to list */
-                    if((tmp_span = H5S__hyper_new_span(span_a->high+1,span_b->high,span_b->down,span_b->next))==NULL)
-                        HGOTO_ERROR(H5E_DATASPACE, H5E_NOSPACE, NULL, "can't allocate hyperslab span")
+                    if(NULL == (tmp_span = H5S__hyper_new_span(span_a->high + 1, span_b->high, span_b->down, span_b->next)))
+                        HGOTO_ERROR(H5E_DATASPACE, H5E_CANTALLOC, NULL, "can't allocate hyperslab span")
 
                     /* Advance span 'a' */
-                    H5S__hyper_recover_span(&recover_a,&span_a,span_a->next);
+                    H5S_HYPER_ADVANCE_SPAN(recover_a, span_a, span_a->next);
 
                     /* Set new span 'b' to tmp_span */
-                    H5S__hyper_recover_span(&recover_b,&span_b,tmp_span);
+                    H5S_HYPER_ADVANCE_SPAN(recover_b, span_b, tmp_span);
                     recover_b = TRUE;
                 } /* end if */
                 else {
                     /* Advance both span 'a' & 'b' */
-                    H5S__hyper_recover_span(&recover_a,&span_a,span_a->next);
-                    H5S__hyper_recover_span(&recover_b,&span_b,span_b->next);
+                    H5S_HYPER_ADVANCE_SPAN(recover_a, span_a, span_a->next);
+                    H5S_HYPER_ADVANCE_SPAN(recover_b, span_b, span_b->next);
                 } /* end else */
             } /* end if */
             /* Check if span 'a' overlaps the lower & upper bound */
@@ -5638,19 +7852,19 @@ H5S__hyper_merge_spans_helper(H5S_hyper_span_info_t *a_spans, H5S_hyper_span_inf
                 /* Check if span 'a' and span 'b' down spans are equal */
                 if(H5S__hyper_cmp_spans(span_a->down, span_b->down)) {
                     /* Merge/add copy of lower & middle parts of span 'a' to merged spans */
-                    if(H5S__hyper_append_span(&prev_span_merge,&merged_spans,span_a->low,span_b->high,span_a->down,NULL)==FAIL)
+                    if(H5S__hyper_append_span(&merged_spans, ndims, span_a->low, span_b->high, span_a->down) < 0)
                         HGOTO_ERROR(H5E_DATASPACE, H5E_CANTAPPEND, NULL, "can't allocate hyperslab span")
                 } /* end if */
                 else {
                     /* Merge/add lower part of span 'a' to merged spans */
-                    if(H5S__hyper_append_span(&prev_span_merge,&merged_spans,span_a->low,span_b->low-1,span_a->down,NULL)==FAIL)
+                    if(H5S__hyper_append_span(&merged_spans, ndims, span_a->low, span_b->low - 1, span_a->down) < 0)
                         HGOTO_ERROR(H5E_DATASPACE, H5E_CANTAPPEND, NULL, "can't allocate hyperslab span")
 
                     /* Get merged span tree for overlapped section */
-                    tmp_spans = H5S__hyper_merge_spans_helper(span_a->down,span_b->down);
+                    tmp_spans = H5S__hyper_merge_spans_helper(span_a->down, span_b->down, ndims - 1);
 
                     /* Merge/add overlapped section to merged spans */
-                    if(H5S__hyper_append_span(&prev_span_merge,&merged_spans,span_b->low,span_b->high,tmp_spans,NULL)==FAIL)
+                    if(H5S__hyper_append_span(&merged_spans, ndims, span_b->low, span_b->high, tmp_spans) < 0)
                         HGOTO_ERROR(H5E_DATASPACE, H5E_CANTAPPEND, NULL, "can't allocate hyperslab span")
 
                     /* Release merged span tree for overlapped section */
@@ -5664,11 +7878,11 @@ H5S__hyper_merge_spans_helper(H5S_hyper_span_info_t *a_spans, H5S_hyper_span_inf
                     HGOTO_ERROR(H5E_DATASPACE, H5E_CANTALLOC, NULL, "can't allocate hyperslab span")
 
                 /* Set new span 'a' to tmp_span */
-                H5S__hyper_recover_span(&recover_a,&span_a,tmp_span);
+                H5S_HYPER_ADVANCE_SPAN(recover_a, span_a, tmp_span);
                 recover_a = TRUE;
 
                 /* Advance span 'b' */
-                H5S__hyper_recover_span(&recover_b,&span_b,span_b->next);
+                H5S_HYPER_ADVANCE_SPAN(recover_b, span_b, span_b->next);
             } /* end if */
             /* Check if span 'a' is entirely within span 'b' */
             /*                AAAAA                  */
@@ -5678,14 +7892,14 @@ H5S__hyper_merge_spans_helper(H5S_hyper_span_info_t *a_spans, H5S_hyper_span_inf
                 /* Check if span 'a' and span 'b' down spans are equal */
                 if(H5S__hyper_cmp_spans(span_a->down, span_b->down)) {
                     /* Merge/add copy of lower & middle parts of span 'b' to merged spans */
-                    if(H5S__hyper_append_span(&prev_span_merge,&merged_spans,span_b->low,span_a->high,span_a->down,NULL)==FAIL)
+                    if(H5S__hyper_append_span(&merged_spans, ndims, span_b->low, span_a->high, span_a->down) < 0)
                         HGOTO_ERROR(H5E_DATASPACE, H5E_CANTAPPEND, NULL, "can't allocate hyperslab span")
                 } /* end if */
                 else {
                     /* Check if there is a lower part of span 'b' */
                     if(span_a->low > span_b->low) {
                         /* Merge/add lower part of span 'b' to merged spans */
-                        if(H5S__hyper_append_span(&prev_span_merge,&merged_spans,span_b->low,span_a->low-1,span_b->down,NULL)==FAIL)
+                        if(H5S__hyper_append_span(&merged_spans, ndims, span_b->low, span_a->low - 1, span_b->down) < 0)
                             HGOTO_ERROR(H5E_DATASPACE, H5E_CANTAPPEND, NULL, "can't allocate hyperslab span")
                     } /* end if */
                     else {
@@ -5693,10 +7907,10 @@ H5S__hyper_merge_spans_helper(H5S_hyper_span_info_t *a_spans, H5S_hyper_span_inf
                     } /* end else */
 
                     /* Get merged span tree for overlapped section */
-                    tmp_spans = H5S__hyper_merge_spans_helper(span_a->down,span_b->down);
+                    tmp_spans = H5S__hyper_merge_spans_helper(span_a->down, span_b->down, ndims - 1);
 
                     /* Merge/add overlapped section to merged spans */
-                    if(H5S__hyper_append_span(&prev_span_merge,&merged_spans,span_a->low,span_a->high,tmp_spans,NULL)==FAIL)
+                    if(H5S__hyper_append_span(&merged_spans, ndims, span_a->low, span_a->high, tmp_spans) < 0)
                         HGOTO_ERROR(H5E_DATASPACE, H5E_CANTAPPEND, NULL, "can't allocate hyperslab span")
 
                     /* Release merged span tree for overlapped section */
@@ -5712,16 +7926,16 @@ H5S__hyper_merge_spans_helper(H5S_hyper_span_info_t *a_spans, H5S_hyper_span_inf
                         HGOTO_ERROR(H5E_DATASPACE, H5E_CANTALLOC, NULL, "can't allocate hyperslab span")
 
                     /* Advance span 'a' */
-                    H5S__hyper_recover_span(&recover_a,&span_a,span_a->next);
+                    H5S_HYPER_ADVANCE_SPAN(recover_a, span_a, span_a->next);
 
                     /* Set new span 'b' to tmp_span */
-                    H5S__hyper_recover_span(&recover_b,&span_b,tmp_span);
+                    H5S_HYPER_ADVANCE_SPAN(recover_b, span_b, tmp_span);
                     recover_b = TRUE;
                 } /* end if */
                 else {
                     /* Advance both spans */
-                    H5S__hyper_recover_span(&recover_a,&span_a,span_a->next);
-                    H5S__hyper_recover_span(&recover_b,&span_b,span_b->next);
+                    H5S_HYPER_ADVANCE_SPAN(recover_a, span_a, span_a->next);
+                    H5S_HYPER_ADVANCE_SPAN(recover_b, span_b, span_b->next);
                 } /* end else */
             } /* end if */
             /* Check if span 'a' overlaps only the upper bound */
@@ -5733,26 +7947,26 @@ H5S__hyper_merge_spans_helper(H5S_hyper_span_info_t *a_spans, H5S_hyper_span_inf
                 /* Check if span 'a' and span 'b' down spans are equal */
                 if(H5S__hyper_cmp_spans(span_a->down, span_b->down)) {
                     /* Merge/add copy of span 'b' to merged spans if so */
-                    if(H5S__hyper_append_span(&prev_span_merge,&merged_spans,span_b->low,span_b->high,span_b->down,NULL)==FAIL)
-                        HGOTO_ERROR(H5E_RESOURCE, H5E_CANTAPPEND, NULL, "can't allocate hyperslab span")
+                    if(H5S__hyper_append_span(&merged_spans, ndims, span_b->low, span_b->high, span_b->down) < 0)
+                        HGOTO_ERROR(H5E_DATASPACE, H5E_CANTAPPEND, NULL, "can't allocate hyperslab span")
                 } /* end if */
                 else {
                     /* Check if there is a lower part of span 'b' */
                     if(span_a->low > span_b->low) {
                         /* Merge/add lower part of span 'b' to merged spans */
-                        if(H5S__hyper_append_span(&prev_span_merge,&merged_spans,span_b->low,span_a->low-1,span_b->down,NULL)==FAIL)
-                            HGOTO_ERROR(H5E_RESOURCE, H5E_CANTAPPEND, NULL, "can't allocate hyperslab span")
+                        if(H5S__hyper_append_span(&merged_spans, ndims, span_b->low, span_a->low - 1, span_b->down) < 0)
+                            HGOTO_ERROR(H5E_DATASPACE, H5E_CANTAPPEND, NULL, "can't allocate hyperslab span")
                     } /* end if */
                     else {
                         /* No lower part of span 'b' , keep going... */
                     } /* end else */
 
                     /* Get merged span tree for overlapped section */
-                    tmp_spans = H5S__hyper_merge_spans_helper(span_a->down,span_b->down);
+                    tmp_spans = H5S__hyper_merge_spans_helper(span_a->down, span_b->down, ndims - 1);
 
                     /* Merge/add overlapped section to merged spans */
-                    if(H5S__hyper_append_span(&prev_span_merge,&merged_spans,span_a->low,span_b->high,tmp_spans,NULL)==FAIL)
-                        HGOTO_ERROR(H5E_RESOURCE, H5E_CANTAPPEND, NULL, "can't allocate hyperslab span")
+                    if(H5S__hyper_append_span(&merged_spans, ndims, span_a->low, span_b->high, tmp_spans) < 0)
+                        HGOTO_ERROR(H5E_DATASPACE, H5E_CANTAPPEND, NULL, "can't allocate hyperslab span")
 
                     /* Release merged span tree for overlapped section */
                     H5S__hyper_free_span_info(tmp_spans);
@@ -5765,11 +7979,11 @@ H5S__hyper_merge_spans_helper(H5S_hyper_span_info_t *a_spans, H5S_hyper_span_inf
                     HGOTO_ERROR(H5E_DATASPACE, H5E_CANTALLOC, NULL, "can't allocate hyperslab span")
 
                 /* Set new span 'a' to tmp_span */
-                H5S__hyper_recover_span(&recover_a,&span_a,tmp_span);
+                H5S_HYPER_ADVANCE_SPAN(recover_a, span_a, tmp_span);
                 recover_a = TRUE;
 
                 /* Advance span 'b' */
-                H5S__hyper_recover_span(&recover_b,&span_b,span_b->next);
+                H5S_HYPER_ADVANCE_SPAN(recover_b, span_b, span_b->next);
             } /* end if */
             /* Span 'a' must be entirely above span 'b' */
             /*                         AAAAA         */
@@ -5777,11 +7991,11 @@ H5S__hyper_merge_spans_helper(H5S_hyper_span_info_t *a_spans, H5S_hyper_span_inf
             /*             BBBBBBBBBB                */
             else {
                 /* Merge/add span 'b' with the merged spans */
-                if(H5S__hyper_append_span(&prev_span_merge,&merged_spans,span_b->low,span_b->high,span_b->down,NULL)==FAIL)
-                    HGOTO_ERROR(H5E_RESOURCE, H5E_CANTAPPEND, NULL, "can't allocate hyperslab span")
+                if(H5S__hyper_append_span(&merged_spans, ndims, span_b->low, span_b->high, span_b->down) < 0)
+                    HGOTO_ERROR(H5E_DATASPACE, H5E_CANTAPPEND, NULL, "can't allocate hyperslab span")
 
                 /* Advance span 'b' */
-                H5S__hyper_recover_span(&recover_b,&span_b,span_b->next);
+                H5S_HYPER_ADVANCE_SPAN(recover_b, span_b, span_b->next);
             } /* end else */
         } /* end while */
 
@@ -5789,11 +8003,11 @@ H5S__hyper_merge_spans_helper(H5S_hyper_span_info_t *a_spans, H5S_hyper_span_inf
         if(span_a != NULL && span_b == NULL) {
             while(span_a != NULL) {
                 /* Merge/add all 'a' spans into the merged spans */
-                if(H5S__hyper_append_span(&prev_span_merge,&merged_spans,span_a->low,span_a->high,span_a->down,NULL)==FAIL)
-                    HGOTO_ERROR(H5E_RESOURCE, H5E_CANTAPPEND, NULL, "can't allocate hyperslab span")
+                if(H5S__hyper_append_span(&merged_spans, ndims, span_a->low, span_a->high, span_a->down) < 0)
+                    HGOTO_ERROR(H5E_DATASPACE, H5E_CANTAPPEND, NULL, "can't allocate hyperslab span")
 
                 /* Advance to next 'a' span, until all processed */
-                H5S__hyper_recover_span(&recover_a,&span_a,span_a->next);
+                H5S_HYPER_ADVANCE_SPAN(recover_a, span_a, span_a->next);
             } /* end while */
         } /* end if */
 
@@ -5801,11 +8015,11 @@ H5S__hyper_merge_spans_helper(H5S_hyper_span_info_t *a_spans, H5S_hyper_span_inf
         if(span_a == NULL && span_b != NULL) {
             while(span_b != NULL) {
                 /* Merge/add all 'b' spans into the merged spans */
-                if(H5S__hyper_append_span(&prev_span_merge,&merged_spans,span_b->low,span_b->high,span_b->down,NULL)==FAIL)
-                    HGOTO_ERROR(H5E_RESOURCE, H5E_CANTAPPEND, NULL, "can't allocate hyperslab span")
+                if(H5S__hyper_append_span(&merged_spans, ndims, span_b->low, span_b->high, span_b->down) < 0)
+                    HGOTO_ERROR(H5E_DATASPACE, H5E_CANTAPPEND, NULL, "can't allocate hyperslab span")
 
                 /* Advance to next 'b' span, until all processed */
-                H5S__hyper_recover_span(&recover_b,&span_b,span_b->next);
+                H5S_HYPER_ADVANCE_SPAN(recover_b, span_b, span_b->next);
             } /* end while */
         } /* end if */
     } /* end else */
@@ -5815,8 +8029,8 @@ H5S__hyper_merge_spans_helper(H5S_hyper_span_info_t *a_spans, H5S_hyper_span_inf
 
 done:
     if(ret_value == NULL)
-        if(merged_spans && H5S__hyper_free_span_info(merged_spans) < 0)
-            HDONE_ERROR(H5E_INTERNAL, H5E_CANTFREE, NULL, "failed to release merged hyperslab spans")
+        if(merged_spans)
+            H5S__hyper_free_span_info(merged_spans);
 
     FUNC_LEAVE_NOAPI(ret_value)
 } /* end H5S__hyper_merge_spans_helper() */
@@ -5833,44 +8047,37 @@ done:
                                         selection.
         H5S_hyper_span_t *new_spans;    IN: Span tree of new spans to add to
                                             hyperslab selection
-        hbool_t can_own;        IN: Flag to indicate that it is OK to point
-                                    directly to the new spans, instead of
-                                    copying them.
  RETURNS
     non-negative on success, negative on failure
  DESCRIPTION
-    Add a set of hyperslab spans to an existing hyperslab selection.  The
-    new spans are required to be non-overlapping with the existing spans in
-    the dataspace's current hyperslab selection.
+    Add a set of hyperslab spans to an existing hyperslab selection.
  GLOBAL VARIABLES
  COMMENTS, BUGS, ASSUMPTIONS
  EXAMPLES
  REVISION LOG
 --------------------------------------------------------------------------*/
 static herr_t
-H5S__hyper_merge_spans(H5S_t *space, H5S_hyper_span_info_t *new_spans, hbool_t can_own)
+H5S__hyper_merge_spans(H5S_t *space, H5S_hyper_span_info_t *new_spans)
 {
-    FUNC_ENTER_NOAPI_NOINIT_NOERR
+    herr_t ret_value = SUCCEED;     /* Return value */
 
-    /* Check args */
+    FUNC_ENTER_STATIC
+
+    /* Sanity checks */
     HDassert(space);
     HDassert(new_spans);
 
     /* If this is the first span tree in the hyperslab selection, just use it */
     if(space->select.sel_info.hslab->span_lst == NULL) {
-        if(can_own)
-            space->select.sel_info.hslab->span_lst = new_spans;
-        else
-            space->select.sel_info.hslab->span_lst = H5S__hyper_copy_span(new_spans);
+        space->select.sel_info.hslab->span_lst = new_spans;
+        space->select.sel_info.hslab->span_lst->count++;
     } /* end if */
     else {
         H5S_hyper_span_info_t *merged_spans;
 
         /* Get the merged spans */
-        merged_spans = H5S__hyper_merge_spans_helper(space->select.sel_info.hslab->span_lst, new_spans);
-
-        /* Sanity checking since we started with some spans, we should still have some after the merge */
-        HDassert(merged_spans);
+        if(NULL == (merged_spans = H5S__hyper_merge_spans_helper(space->select.sel_info.hslab->span_lst, new_spans, space->extent.rank)))
+            HGOTO_ERROR(H5E_DATASPACE, H5E_CANTMERGE, FAIL, "can't merge hyperslab spans")
 
         /* Free the previous spans */
         H5S__hyper_free_span_info(space->select.sel_info.hslab->span_lst);
@@ -5879,18 +8086,21 @@ H5S__hyper_merge_spans(H5S_t *space, H5S_hyper_span_info_t *new_spans, hbool_t c
         space->select.sel_info.hslab->span_lst = merged_spans;
     } /* end else */
 
-    FUNC_LEAVE_NOAPI(SUCCEED)
+done:
+    FUNC_LEAVE_NOAPI(ret_value)
 } /* end H5S__hyper_merge_spans() */
 
 
 /*--------------------------------------------------------------------------
  NAME
-    H5S__hyper_spans_nelem
+    H5S__hyper_spans_nelem_helper
  PURPOSE
     Count the number of elements in a span tree
  USAGE
-    hsize_t H5S__hyper_spans_nelem(spans)
+    hsize_t H5S__hyper_spans_nelem_helper(spans, op_info_i, op_gen)
         const H5S_hyper_span_info_t *spans; IN: Hyperslan span tree to count elements of
+        unsigned op_info_i;             IN: Index of op info to use
+        uint64_t op_gen;                IN: Operation generation
  RETURNS
     Number of elements in span tree on success; negative on failure
  DESCRIPTION
@@ -5901,33 +8111,147 @@ H5S__hyper_merge_spans(H5S_t *space, H5S_hyper_span_info_t *new_spans, hbool_t c
  REVISION LOG
 --------------------------------------------------------------------------*/
 static hsize_t
-H5S__hyper_spans_nelem(const H5S_hyper_span_info_t *spans)
+H5S__hyper_spans_nelem_helper(H5S_hyper_span_info_t *spans, unsigned op_info_i,
+    uint64_t op_gen)
 {
     hsize_t ret_value = 0;          /* Return value */
 
     FUNC_ENTER_STATIC_NOERR
 
-    /* Count the number of elements in the span tree */
-    if(spans != NULL) {
+    /* Sanity check */
+    HDassert(spans);
+
+    /* Check if the span tree was already counted */
+    if(spans->op_info[op_info_i].op_gen == op_gen)
+        /* Just return the # of elements in the already counted span tree */
+        ret_value = spans->op_info[op_info_i].u.nelmts;
+    else {      /* Count the number of elements in the span tree */
         const H5S_hyper_span_t *span;     /* Hyperslab span */
 
         span = spans->head;
-        while(span != NULL) {
-            /* If there are down spans, multiply the size of this span by the total down span elements */
-            if(span->down != NULL)
-                ret_value += span->nelem * H5S__hyper_spans_nelem(span->down);
-            /* If there are no down spans, just count the elements in this span */
-            else
-                ret_value += span->nelem;
+        if(NULL == span->down) {
+            while(span != NULL) {
+                /* Compute # of elements covered */
+                ret_value += (span->high - span->low) + 1;
 
-            /* Advance to next span */
-            span = span->next;
-        } /* end while */
+                /* Advance to next span */
+                span = span->next;
+            } /* end while */
+        } /* end if */
+        else {
+            while(span != NULL) {
+                hsize_t nelmts;     /* # of elements covered by current span */
+
+                /* Compute # of elements covered */
+                nelmts = (span->high - span->low) + 1;
+
+                /* Multiply the size of this span by the total down span elements */
+                ret_value += nelmts * H5S__hyper_spans_nelem_helper(span->down, op_info_i, op_gen);
+
+                /* Advance to next span */
+                span = span->next;
+            } /* end while */
+        } /* end else */
+
+        /* Set the operation generation for this span tree, to avoid re-computing */
+        spans->op_info[op_info_i].op_gen = op_gen;
+
+        /* Hold a copy of the # of elements */
+        spans->op_info[op_info_i].u.nelmts = ret_value;
     } /* end else */
 
     FUNC_LEAVE_NOAPI(ret_value)
+} /* end H5S__hyper_spans_nelem_helper() */
+
+
+/*--------------------------------------------------------------------------
+ NAME
+    H5S__hyper_spans_nelem
+ PURPOSE
+    Count the number of elements in a span tree
+ USAGE
+    hsize_t H5S__hyper_spans_nelem(spans)
+        const H5S_hyper_span_info_t *spans; IN: Hyperslan span tree to count elements of
+ RETURNS
+    Number of elements in span tree on success; negative on failure
+ DESCRIPTION
+    Counts the number of elements described by the spans in a span tree.
+ GLOBAL VARIABLES
+ COMMENTS, BUGS, ASSUMPTIONS
+ EXAMPLES
+ REVISION LOG
+--------------------------------------------------------------------------*/
+static hsize_t
+H5S__hyper_spans_nelem(H5S_hyper_span_info_t *spans)
+{
+    uint64_t op_gen;            /* Operation generation value */
+    hsize_t ret_value = 0;      /* Return value */
+
+    FUNC_ENTER_STATIC_NOERR
+
+    /* Sanity check */
+    HDassert(spans);
+
+    /* Acquire an operation generation value for this operation */
+    op_gen = H5S__hyper_get_op_gen();
+
+    /* Count the number of elements in the span tree */
+    /* Always use op_info[0] since we own this op_info, so there can be no
+     * simultaneous operations */
+    ret_value = H5S__hyper_spans_nelem_helper(spans, 0, op_gen);
+
+    FUNC_LEAVE_NOAPI(ret_value)
 } /* end H5S__hyper_spans_nelem() */
 
+
+/*--------------------------------------------------------------------------
+ NAME
+    H5S__hyper_add_disjoint_spans
+ PURPOSE
+    Add new hyperslab spans to existing hyperslab selection in the case the
+    new hyperslab spans don't overlap with the existing hyperslab selection
+ USAGE
+    herr_t H5S__hyper_add_disjoint_spans(space, new_spans)
+        H5S_t *space;             IN: Dataspace to add new spans to hyperslab
+                                        selection.
+        H5S_hyper_span_t *new_spans;    IN: Span tree of new spans to add to
+                                            hyperslab selection
+ RETURNS
+    Non-negative on success, negative on failure
+ DESCRIPTION
+    Add a set of hyperslab spans to an existing hyperslab selection.  The
+    new spans are required not to overlap with the existing spans in the
+    dataspace's current hyperslab selection in terms of bound box.
+ GLOBAL VARIABLES
+ COMMENTS, BUGS, ASSUMPTIONS
+ EXAMPLES
+ REVISION LOG
+--------------------------------------------------------------------------*/
+static herr_t
+H5S__hyper_add_disjoint_spans(H5S_t *space, H5S_hyper_span_info_t *new_spans)
+{
+    herr_t ret_value = SUCCEED;     /* Return value */
+
+    FUNC_ENTER_STATIC
+
+    /* Check args */
+    HDassert(space);
+    HDassert(new_spans);
+
+    /* Update the number of elements in the selection */
+    space->select.num_elem += H5S__hyper_spans_nelem(new_spans);
+
+    /* Add the new spans to the existing selection in the dataspace */
+    if(H5S__hyper_merge_spans(space, new_spans) < 0)
+        HGOTO_ERROR(H5E_DATASPACE, H5E_CANTINSERT, FAIL, "can't merge hyperslabs")
+
+    /* Free the memory space for new spans */
+    H5S__hyper_free_span_info(new_spans);
+
+done:
+    FUNC_LEAVE_NOAPI(ret_value)
+} /* end H5S__hyper_add_disjoint_spans */
+
 
 /*--------------------------------------------------------------------------
  NAME
@@ -5936,12 +8260,12 @@ H5S__hyper_spans_nelem(const H5S_hyper_span_info_t *spans)
     Create a span tree
  USAGE
     H5S_hyper_span_t *H5S__hyper_make_spans(rank, start, stride, count, block)
-        unsigned rank;               IN: # of dimensions of the space
-        const hsize_t *start;    IN: Starting location of the hyperslabs
-        const hsize_t *stride;    IN: Stride from the beginning of one block to
+        unsigned rank;          IN: # of dimensions of the space
+        const hsize_t *start;   IN: Starting location of the hyperslabs
+        const hsize_t *stride;  IN: Stride from the beginning of one block to
                                         the next
-        const hsize_t *count;     IN: Number of blocks
-        const hsize_t *block;     IN: Size of hyperslab block
+        const hsize_t *count;   IN: Number of blocks
+        const hsize_t *block;   IN: Size of hyperslab block
  RETURNS
     Pointer to new span tree on success, NULL on failure
  DESCRIPTION
@@ -5961,9 +8285,7 @@ H5S__hyper_make_spans(unsigned rank, const hsize_t *start, const hsize_t *stride
     H5S_hyper_span_info_t *down = NULL;     /* Pointer to spans in next dimension down */
     H5S_hyper_span_t      *last_span;       /* Current position in hyperslab span list */
     H5S_hyper_span_t      *head = NULL;     /* Head of new hyperslab span list */
-    hsize_t                stride_iter;     /* Iterator over the stride values */
     int                    i;               /* Counters */
-    unsigned               u;               /* Counters */
     H5S_hyper_span_info_t *ret_value = NULL;    /* Return value */
 
     FUNC_ENTER_STATIC
@@ -5977,6 +8299,9 @@ H5S__hyper_make_spans(unsigned rank, const hsize_t *start, const hsize_t *stride
 
     /* Start creating spans in fastest changing dimension */
     for(i = (int)(rank - 1); i >= 0; i--) {
+        hsize_t curr_low, curr_high;    /* Current low & high values */
+        hsize_t dim_stride;             /* Current dim's stride */
+        unsigned u;                     /* Local index variable */
 
         /* Sanity check */
         if(0 == count[i])
@@ -5987,8 +8312,10 @@ H5S__hyper_make_spans(unsigned rank, const hsize_t *start, const hsize_t *stride
         last_span = NULL;
 
         /* Generate all the span segments for this dimension */
-        for(u = 0, stride_iter = 0; u < count[i]; u++, stride_iter += stride[i])
-        {
+        curr_low = start[i];
+        curr_high = start[i] + (block[i] - 1);
+        dim_stride = stride[i];
+        for(u = 0; u < count[i]; u++, curr_low += dim_stride, curr_high += dim_stride) {
             H5S_hyper_span_t      *span;            /* New hyperslab span */
 
             /* Allocate a span node */
@@ -5996,12 +8323,14 @@ H5S__hyper_make_spans(unsigned rank, const hsize_t *start, const hsize_t *stride
                 HGOTO_ERROR(H5E_DATASPACE, H5E_CANTALLOC, NULL, "can't allocate hyperslab span")
 
             /* Set the span's basic information */
-            span->low = start[i] + stride_iter;
-            span->high = span->low + (block[i] - 1);
-            span->nelem = block[i];
-            span->pstride = stride[i];
+            span->low = curr_low;
+            span->high = curr_high;
             span->next = NULL;
 
+            /* Set the information for the next dimension down's spans */
+            /* (Will be NULL for fastest changing dimension) */
+            span->down = down;
+
             /* Append to the list of spans in this dimension */
             if(head == NULL)
                 head = span;
@@ -6010,23 +8339,32 @@ H5S__hyper_make_spans(unsigned rank, const hsize_t *start, const hsize_t *stride
 
             /* Move current pointer */
             last_span = span;
-
-            /* Set the information for the next dimension down's spans, if appropriate */
-            if(down != NULL) {
-                span->down = down;
-                down->count++;  /* Increment reference count for shared span */
-            } /* end if */
-            else
-                span->down = NULL;
         } /* end for */
 
+        /* Increment ref. count of shared span */
+        if(down != NULL)
+            down->count = (unsigned)count[i];
+
         /* Allocate a span info node */
-        if(NULL == (down = H5FL_CALLOC(H5S_hyper_span_info_t)))
+        if(NULL == (down = H5S__hyper_new_span_info(rank)))
             HGOTO_ERROR(H5E_DATASPACE, H5E_CANTALLOC, NULL, "can't allocate hyperslab span")
 
         /* Keep the pointer to the next dimension down's completed list */
         down->head = head;
 
+        /* Keep the tail pointer to the next dimension down's completed list */
+        down->tail = last_span;
+
+        /* Set the low & high bounds for this dimension */
+        down->low_bounds[0] = down->head->low;
+        down->high_bounds[0] = down->tail->high;
+
+        /* Copy bounds from lower dimensions */
+        /* (head & tail pointers share lower dimensions, so using either is OK) */
+        if(head->down) {
+            H5MM_memcpy(&down->low_bounds[1], &head->down->low_bounds[0], sizeof(hsize_t) * ((rank - 1) - (unsigned)i));
+            H5MM_memcpy(&down->high_bounds[1], &head->down->high_bounds[0], sizeof(hsize_t) * ((rank - 1) - (unsigned)i));
+        } /* end if */
     } /* end for */
 
     /* Indicate that there is a pointer to this tree */
@@ -6047,7 +8385,7 @@ done:
             do {
                 if(down) {
                     head = down->head;
-                    down = H5FL_FREE(H5S_hyper_span_info_t, down);
+                    down = (H5S_hyper_span_info_t *)H5FL_ARR_FREE(hbounds_t, down);
                 } /* end if */
                 down = head->down;
 
@@ -6063,6 +8401,224 @@ done:
     FUNC_LEAVE_NOAPI(ret_value)
 } /* end H5S__hyper_make_spans() */
 
+
+/*--------------------------------------------------------------------------
+ NAME
+    H5S__hyper_update_diminfo
+ PURPOSE
+    Attempt to update optimized hyperslab information quickly.  (It can be
+    recovered with regular selection).  If this algorithm cannot determine
+    the optimized dimension info quickly, this function will simply mark it
+    as invalid and unknown if it can be built (H5S_DIMINFO_VALID_NO), so
+    H5S__hyper_rebuild can be run later to determine for sure.
+ USAGE
+    herr_t H5S__hyper_update_diminfo(space, op, new_hyper_diminfo)
+        H5S_t *space;       IN: Dataspace to check
+        H5S_seloper_t op;   IN: The operation being performed on the
+                                selection
+        const H5S_hyper_dim_t new_hyper_diminfo; IN: The new selection that
+                                                     is being combined with
+                                                     the current
+ RETURNS
+    >=0 on success, <0 on failure
+ DESCRIPTION
+    Examine the span tree for a hyperslab selection and rebuild
+    the start/stride/count/block information for the selection, if possible.
+
+ GLOBAL VARIABLES
+ COMMENTS, BUGS, ASSUMPTIONS
+ EXAMPLES
+ REVISION LOG
+--------------------------------------------------------------------------*/
+static herr_t
+H5S__hyper_update_diminfo(H5S_t *space, H5S_seloper_t op,
+    const H5S_hyper_dim_t *new_hyper_diminfo)
+{
+    herr_t ret_value = SUCCEED;      /* Return value */
+
+    FUNC_ENTER_STATIC_NOERR
+
+    /* Check args */
+    HDassert(space);
+    HDassert(new_hyper_diminfo);
+
+    /* Check for conditions that prevent us from using the fast algorithm here */
+    /* (and instead require H5S__hyper_rebuild) */
+    if(!((op == H5S_SELECT_OR) || (op == H5S_SELECT_XOR))
+            || space->select.sel_info.hslab->diminfo_valid != H5S_DIMINFO_VALID_YES
+            || !space->select.sel_info.hslab->span_lst->head)
+        space->select.sel_info.hslab->diminfo_valid = H5S_DIMINFO_VALID_NO;
+    else {
+        H5S_hyper_dim_t tmp_diminfo[H5S_MAX_RANK];  /* Temporary dimension info */
+        hbool_t found_nonidentical_dim = FALSE;
+        unsigned curr_dim;
+
+        /* Copy current diminfo.opt values */
+        H5MM_memcpy(tmp_diminfo, space->select.sel_info.hslab->diminfo.opt, sizeof(tmp_diminfo));
+
+        /* Loop over dimensions */
+        for(curr_dim = 0; curr_dim < space->extent.rank; curr_dim++) {
+            /* Check for this being identical */
+            if((tmp_diminfo[curr_dim].start != new_hyper_diminfo[curr_dim].start)
+                    || (tmp_diminfo[curr_dim].stride != new_hyper_diminfo[curr_dim].stride)
+                    || (tmp_diminfo[curr_dim].count != new_hyper_diminfo[curr_dim].count)
+                    || (tmp_diminfo[curr_dim].block != new_hyper_diminfo[curr_dim].block)) {
+                hsize_t high_start, high_count, high_block;         /* The start, count & block values for the higher block */
+
+                /* Dimension is not identical */
+                /* Check if we already found a nonidentical dim - only one is
+                 * allowed */
+                if(found_nonidentical_dim) {
+                    space->select.sel_info.hslab->diminfo_valid = H5S_DIMINFO_VALID_NO;
+                    break;
+                } /* end if */
+
+                /* Check that strides are the same, or count is 1 for one of the
+                 * slabs */
+                if((tmp_diminfo[curr_dim].stride != new_hyper_diminfo[curr_dim].stride)
+                        && (tmp_diminfo[curr_dim].count > 1)
+                        && (new_hyper_diminfo[curr_dim].count > 1)) {
+                    space->select.sel_info.hslab->diminfo_valid = H5S_DIMINFO_VALID_NO;
+                    break;
+                } /* end if */
+
+                /* Patch tmp_diminfo.stride if its count is 1 */
+                if((tmp_diminfo[curr_dim].count == 1)
+                        && (new_hyper_diminfo[curr_dim].count > 1))
+                    tmp_diminfo[curr_dim].stride = new_hyper_diminfo[curr_dim].stride;
+
+                /* Determine lowest start, and set tmp_diminfo.start, count and
+                 *  block to use the lowest, and high_start, high_count and
+                 *  high_block to use the highest
+                 */
+                if(tmp_diminfo[curr_dim].start < new_hyper_diminfo[curr_dim].start) {
+                    high_start = new_hyper_diminfo[curr_dim].start;
+                    high_count = new_hyper_diminfo[curr_dim].count;
+                    high_block = new_hyper_diminfo[curr_dim].block;
+                } /* end if */
+                else {
+                    high_start = tmp_diminfo[curr_dim].start;
+                    tmp_diminfo[curr_dim].start = new_hyper_diminfo[curr_dim].start;
+                    high_count = tmp_diminfo[curr_dim].count;
+                    tmp_diminfo[curr_dim].count = new_hyper_diminfo[curr_dim].count;
+                    high_block = tmp_diminfo[curr_dim].block;
+                    tmp_diminfo[curr_dim].block = new_hyper_diminfo[curr_dim].block;
+                } /* end else */
+
+                /* If count is 1 for both slabs, take different actions */
+                if((tmp_diminfo[curr_dim].count == 1) && (high_count == 1)) {
+                    /* Check for overlap */
+                    if((tmp_diminfo[curr_dim].start + tmp_diminfo[curr_dim].block)
+                            > high_start) {
+                        /* Check operation type */
+                        if(op == H5S_SELECT_OR)
+                            /* Merge blocks */
+                            tmp_diminfo[curr_dim].block = ((high_start + high_block)
+                                    >= (tmp_diminfo[curr_dim].start + tmp_diminfo[curr_dim].block))
+                                    ? (high_start + high_block - tmp_diminfo[curr_dim].start)
+                                    : tmp_diminfo[curr_dim].block;
+                        else {
+                            /* Block values must be the same */
+                            if(tmp_diminfo[curr_dim].block != high_block) {
+                                space->select.sel_info.hslab->diminfo_valid = H5S_DIMINFO_VALID_NO;
+                                break;
+                            } /* end if */
+
+                            /* XOR - overlap creates 2 blocks */
+                            tmp_diminfo[curr_dim].stride = high_block;
+                            tmp_diminfo[curr_dim].count = 2;
+                            tmp_diminfo[curr_dim].block = high_start - tmp_diminfo[curr_dim].start;
+                        } /* end else */
+                    } /* end if */
+                    else if((tmp_diminfo[curr_dim].start + tmp_diminfo[curr_dim].block)
+                            == high_start)
+                        /* Blocks border, merge them */
+                        tmp_diminfo[curr_dim].block += high_block;
+                    else {
+                        /* Distinct blocks */
+                        /* Block values must be the same */
+                        if(tmp_diminfo[curr_dim].block != high_block) {
+                            space->select.sel_info.hslab->diminfo_valid = H5S_DIMINFO_VALID_NO;
+                            break;
+                        } /* end if */
+
+                        /* Create strided selection */
+                        tmp_diminfo[curr_dim].stride = high_start - tmp_diminfo[curr_dim].start;
+                        tmp_diminfo[curr_dim].count = 2;
+                    } /* end else */
+                } /* end if */
+                else {
+                    /* Check if block values are the same */
+                    if(tmp_diminfo[curr_dim].block != new_hyper_diminfo[curr_dim].block) {
+                        space->select.sel_info.hslab->diminfo_valid = H5S_DIMINFO_VALID_NO;
+                        break;
+                    } /* end if */
+
+                    /* Check phase of strides */
+                    if((tmp_diminfo[curr_dim].start % tmp_diminfo[curr_dim].stride)
+                            != (new_hyper_diminfo[curr_dim].start % tmp_diminfo[curr_dim].stride)) {
+                        space->select.sel_info.hslab->diminfo_valid = H5S_DIMINFO_VALID_NO;
+                        break;
+                    } /* end if */
+
+                    /* Check operation type */
+                    if(op == H5S_SELECT_OR) {
+                        /* Make sure the slabs border or overlap */
+                        if(high_start > (tmp_diminfo[curr_dim].start
+                                + (tmp_diminfo[curr_dim].count
+                                * tmp_diminfo[curr_dim].stride))) {
+                            space->select.sel_info.hslab->diminfo_valid = H5S_DIMINFO_VALID_NO;
+                            break;
+                        } /* end if */
+                    } /* end if */
+                    else
+                        /* XOR: Make sure the slabs border */
+                        if(high_start != (tmp_diminfo[curr_dim].start
+                                + (tmp_diminfo[curr_dim].count
+                                * tmp_diminfo[curr_dim].stride))) {
+                            space->select.sel_info.hslab->diminfo_valid = H5S_DIMINFO_VALID_NO;
+                            break;
+                        } /* end if */
+
+                    /* Set count for combined selection */
+                    tmp_diminfo[curr_dim].count = ((high_start
+                            - tmp_diminfo[curr_dim].start)
+                            / tmp_diminfo[curr_dim].stride) + high_count;
+                } /* end else */
+
+                /* Indicate that we found a nonidentical dim */
+                found_nonidentical_dim = TRUE;
+            } /* end if */
+        } /* end for */
+
+        /* Check if we succeeded, if so, set the new diminfo values */
+        if(space->select.sel_info.hslab->diminfo_valid == H5S_DIMINFO_VALID_YES)
+            for(curr_dim = 0; curr_dim < space->extent.rank; curr_dim++) {
+                hsize_t tmp_high_bound;
+
+                /* Set the new diminfo values */
+                space->select.sel_info.hslab->diminfo.app[curr_dim].start  = space->select.sel_info.hslab->diminfo.opt[curr_dim].start = tmp_diminfo[curr_dim].start;
+                HDassert(tmp_diminfo[curr_dim].stride > 0);
+                space->select.sel_info.hslab->diminfo.app[curr_dim].stride = space->select.sel_info.hslab->diminfo.opt[curr_dim].stride = tmp_diminfo[curr_dim].stride;
+                HDassert(tmp_diminfo[curr_dim].count > 0);
+                space->select.sel_info.hslab->diminfo.app[curr_dim].count  = space->select.sel_info.hslab->diminfo.opt[curr_dim].count = tmp_diminfo[curr_dim].count;
+                HDassert(tmp_diminfo[curr_dim].block > 0);
+                space->select.sel_info.hslab->diminfo.app[curr_dim].block  = space->select.sel_info.hslab->diminfo.opt[curr_dim].block = tmp_diminfo[curr_dim].block;
+
+                /* Check for updating the low & high bounds */
+                if(tmp_diminfo[curr_dim].start < space->select.sel_info.hslab->diminfo.low_bounds[curr_dim])
+                    space->select.sel_info.hslab->diminfo.low_bounds[curr_dim] = tmp_diminfo[curr_dim].start;
+                tmp_high_bound = tmp_diminfo[curr_dim].start +
+                    (tmp_diminfo[curr_dim].block - 1) +
+                    (tmp_diminfo[curr_dim].stride * (tmp_diminfo[curr_dim].count - 1));
+                if(tmp_high_bound > space->select.sel_info.hslab->diminfo.low_bounds[curr_dim])
+                    space->select.sel_info.hslab->diminfo.high_bounds[curr_dim] = tmp_high_bound;
+            } /* end for */
+    } /* end else */
+
+    FUNC_LEAVE_NOAPI(ret_value)
+} /* end H5S__hyper_update_diminfo() */
+
 
 /*--------------------------------------------------------------------------
  NAME
@@ -6072,9 +8628,8 @@ done:
     (It can be recovered with regular selection)
  USAGE
     herr_t H5S__hyper_rebuild_helper(space)
-        const H5S_hyper_span_t *span;   IN: Portion of span tree to check
-        H5S_hyper_dim_t span_slab[];    OUT: Rebuilt section of hyperslab description
-        unsigned rank;                  IN: Current dimension to work on
+        const H5S_hyper_span_t *spans;  IN: Portion of span tree to check
+        H5S_hyper_dim_t span_slab_info[]; OUT: Rebuilt section of hyperslab description
  RETURNS
     TRUE/FALSE for hyperslab selection rebuilt
  DESCRIPTION
@@ -6089,108 +8644,85 @@ done:
     KY, 2005/9/22
 --------------------------------------------------------------------------*/
 static hbool_t
-H5S__hyper_rebuild_helper(const H5S_hyper_span_t *span, H5S_hyper_dim_t span_slab_info[],
-    unsigned rank)
+H5S__hyper_rebuild_helper(const H5S_hyper_span_info_t *spans, H5S_hyper_dim_t span_slab_info[])
 {
+    const H5S_hyper_span_t *span;       /* Hyperslab span */
+    const H5S_hyper_span_t *prev_span;  /* Previous span in list */
+    hsize_t start;              /* Starting element for this dimension */
+    hsize_t stride;             /* Stride for this dimension */
+    hsize_t block;              /* Block size for this dimension */
+    hsize_t prev_low;           /* Low bound for previous span */
+    size_t spancount;           /* Number of spans encountered in this dimension */
     hbool_t ret_value = TRUE;   /* Return value */
 
     FUNC_ENTER_STATIC_NOERR
 
-    if(span) {
-        const H5S_hyper_span_t *prev_span = NULL;     /* Previous span in list */
-        H5S_hyper_dim_t canon_down_span_slab_info[H5S_MAX_RANK];
-        hsize_t curr_stride;
-        hsize_t curr_block;
-        hsize_t curr_start;
-        hsize_t curr_low;
-        size_t outcount;        /* Number of spans encountered in this dimension */
-
-        /* Initialization */
-        curr_stride = 1;
-        curr_low = 0;
-        outcount = 0;
-
-        /* Get "canonical" down span information */
-        if(span->down) {
-            HDassert(span->down->head);
-
-            /* Go to the next down span and check whether the selection can be rebuilt */
-            if(!H5S__hyper_rebuild_helper(span->down->head, span_slab_info, rank - 1))
-                HGOTO_DONE(FALSE)
-
-            H5MM_memcpy(canon_down_span_slab_info, span_slab_info, sizeof(H5S_hyper_dim_t) * rank);
-        } /* end if */
+    /* Sanity check */
+    HDassert(spans);
 
-        /* Assign the initial starting point & block size */
-        curr_start = span->low;
-        curr_block = (span->high - span->low) + 1;
+    /* Initialization */
+    span = spans->head;
+    stride = 1;
+    prev_low = 0;
+    spancount = 0;
 
-        /* Loop the spans */
-        while(span) {
-            if(outcount > 0) {
-                hsize_t next_stride;    /* Stride from previous span */
-                hsize_t next_block;     /* Block size of current span */
+    /* Get "canonical" down span information */
+    if(span->down)
+        /* Go to the next down span and check whether the selection can be rebuilt */
+        if(!H5S__hyper_rebuild_helper(span->down, &span_slab_info[1]))
+            HGOTO_DONE(FALSE)
 
-                /* Check that down spans match current slab info */
-                /* (Can skip check if previous span's down pointer is same as current one) */
-                if(span->down && (NULL == prev_span || prev_span->down != span->down)) {
-                    H5S_hyper_dim_t *curr_down_span_slab_info;
-                    unsigned u;                 /* Local index variable */
+    /* Assign the initial starting point & block size for this dimension */
+    start = span->low;
+    block = (span->high - span->low) + 1;
 
-                    HDassert(span->down->head);
+    /* Loop the spans */
+    prev_span = NULL;
+    while(span) {
+        if(spancount > 0) {
+            hsize_t curr_stride;    /* Current stride from previous span */
+            hsize_t curr_block;     /* Block size of current span */
 
-                    /* Go to the next down span and check whether the selection can be rebuilt.*/
-                    if(!H5S__hyper_rebuild_helper(span->down->head, span_slab_info, rank - 1))
-                        HGOTO_DONE(FALSE)
+            /* Sanity check */
+            HDassert(prev_span);
 
-                    /* Compare the slab information of the adjacent spans in the down span tree.
-                       We have to compare all the sub-tree slab information with the canon_down_span_slab_info.*/
-                    for(u = 0; u < rank - 1; u++) {
-                       curr_down_span_slab_info = &span_slab_info[u];
-
-                       if(curr_down_span_slab_info->count > 0 && canon_down_span_slab_info[u].count > 0) {
-                          if(curr_down_span_slab_info->start != canon_down_span_slab_info[u].start
-                              || curr_down_span_slab_info->stride != canon_down_span_slab_info[u].stride
-                              || curr_down_span_slab_info->block != canon_down_span_slab_info[u].block
-                              || curr_down_span_slab_info->count != canon_down_span_slab_info[u].count)
-                          HGOTO_DONE(FALSE)
-                       } /* end if */
-                       else if(!((curr_down_span_slab_info->count == 0) && (canon_down_span_slab_info[u].count == 0)))
-                          HGOTO_DONE(FALSE)
-                    } /* end for */
-                } /* end if */
+            /* Check that down spans match current slab info */
+            /* (Can skip check if previous span's down pointer is same as current one) */
+            if(span->down && prev_span->down != span->down)
+                if(!H5S__hyper_cmp_spans(span->down, prev_span->down))
+                    HGOTO_DONE(FALSE)
 
-                /* Obtain values for stride and block */
-                next_stride = span->low  - curr_low;
-                next_block = (span->high - span->low) + 1;
+            /* Obtain values for stride and block */
+            curr_stride = span->low - prev_low;
+            curr_block = (span->high - span->low) + 1;
 
-                /* Compare stride and block in this span, to compare stride,
-                 * three spans are needed. Account for the first two spans.
-                 */
-                if(next_block != curr_block)
-                    HGOTO_DONE(FALSE)
-                if(outcount > 1 && curr_stride != next_stride)
+            /* Compare stride and block for this span.  To compare stride,
+             * three spans are needed.  Account for the first two spans.
+             */
+            if(curr_block != block)
+                HGOTO_DONE(FALSE)
+            if(spancount > 1) {
+                if(stride != curr_stride)
                     HGOTO_DONE(FALSE)
-
-                /* Keep the isolated stride to be 1 */
-                curr_stride = next_stride;
             } /* end if */
+            else
+                stride = curr_stride;
+        } /* end if */
 
-            /* Keep current starting point */
-            curr_low = span->low;
+        /* Keep current starting point */
+        prev_low = span->low;
 
-            /* Advance to next span */
-            prev_span = span;
-            span = span->next;
-            outcount++;
-        } /* end while */
+        /* Advance to next span */
+        prev_span = span;
+        span = span->next;
+        spancount++;
+    } /* end while */
 
-        /* Save the span information. */
-        span_slab_info[rank - 1].start  = curr_start;
-        span_slab_info[rank - 1].count  = outcount;
-        span_slab_info[rank - 1].block  = curr_block;
-        span_slab_info[rank - 1].stride = curr_stride;
-    } /* end if */
+    /* Save the span information. */
+    span_slab_info[0].start  = start;
+    span_slab_info[0].count  = spancount;
+    span_slab_info[0].block  = block;
+    span_slab_info[0].stride = stride;
 
 done:
     FUNC_LEAVE_NOAPI(ret_value)
@@ -6204,13 +8736,13 @@ done:
     Rebuild optimized hyperslab information if possible.
     (It can be recovered with regular selection)
  USAGE
-    hbool_t H5S__hyper_rebuild(space)
-        const H5S_t *space;     IN: Dataspace to check
+    void H5S__hyper_rebuild(space)
+        H5S_t *space;     IN: Dataspace to check
  RETURNS
-    TRUE/FALSE for hyperslab selection rebuilt
+    None
  DESCRIPTION
-    Examine the span tree for a hyperslab selection and rebuild
-    the start/stride/count/block information for the selection, if possible.
+    Examine the span tree for a hyperslab selection and rebuild a regular
+    start/stride/count/block hyperslab selection, if possible.
  GLOBAL VARIABLES
  COMMENTS, BUGS, ASSUMPTIONS
     To be able to recover the optimized information, the span tree must conform
@@ -6218,47 +8750,32 @@ done:
  EXAMPLES
  REVISION LOG
 --------------------------------------------------------------------------*/
-static hbool_t
+void
 H5S__hyper_rebuild(H5S_t *space)
 {
-    H5S_hyper_dim_t top_span_slab_info[H5S_MAX_RANK];
-    unsigned rank, curr_dim;
-    hbool_t ret_value = TRUE;      /* Return value */
+    H5S_hyper_dim_t rebuilt_slab_info[H5S_MAX_RANK];
 
-    FUNC_ENTER_STATIC_NOERR
+    FUNC_ENTER_PACKAGE_NOERR
 
     /* Check args */
     HDassert(space);
     HDassert(space->select.sel_info.hslab->span_lst);
 
-    /* Check the rank of space */
-    rank = space->extent.rank;
-
-    /* Check whether the slab can be rebuilt. Only regular selection can be rebuilt. If yes, fill in correct values.*/
-    if(!H5S__hyper_rebuild_helper(space->select.sel_info.hslab->span_lst->head, top_span_slab_info, rank)) {
-        HGOTO_DONE(FALSE)
-    } /* end if */
+    /* Check whether the slab can be rebuilt */
+    /* (Only regular selection can be rebuilt. If yes, fill in correct values) */
+    if(FALSE == H5S__hyper_rebuild_helper(space->select.sel_info.hslab->span_lst, rebuilt_slab_info))
+        space->select.sel_info.hslab->diminfo_valid = H5S_DIMINFO_VALID_IMPOSSIBLE;
     else {
-        H5S_hyper_dim_t *diminfo;
-        H5S_hyper_dim_t *app_diminfo;
-
-        diminfo = space->select.sel_info.hslab->diminfo.opt;
-        app_diminfo = space->select.sel_info.hslab->diminfo.app;
-
-        for(curr_dim = 0; curr_dim < rank; curr_dim++) {
-
-            app_diminfo[(rank - curr_dim) - 1].start  = diminfo[(rank - curr_dim) - 1].start = top_span_slab_info[curr_dim].start;
-            app_diminfo[(rank - curr_dim) - 1].stride = diminfo[(rank - curr_dim) - 1].stride = top_span_slab_info[curr_dim].stride;
-            app_diminfo[(rank - curr_dim) - 1].count  = diminfo[(rank - curr_dim) - 1].count = top_span_slab_info[curr_dim].count;
-            app_diminfo[(rank - curr_dim) - 1].block  = diminfo[(rank - curr_dim) - 1].block = top_span_slab_info[curr_dim].block;
-
-        }
+        /* Set the dimension info & bounds for the dataspace, from the rebuilt info */
+        H5MM_memcpy(space->select.sel_info.hslab->diminfo.app, rebuilt_slab_info, sizeof(rebuilt_slab_info));
+        H5MM_memcpy(space->select.sel_info.hslab->diminfo.opt, rebuilt_slab_info, sizeof(rebuilt_slab_info));
+        H5MM_memcpy(space->select.sel_info.hslab->diminfo.low_bounds, space->select.sel_info.hslab->span_lst->low_bounds, sizeof(hsize_t) * space->extent.rank);
+        H5MM_memcpy(space->select.sel_info.hslab->diminfo.high_bounds, space->select.sel_info.hslab->span_lst->high_bounds, sizeof(hsize_t) * space->extent.rank);
 
         space->select.sel_info.hslab->diminfo_valid = H5S_DIMINFO_VALID_YES;
     } /* end else */
 
-done:
-    FUNC_LEAVE_NOAPI(ret_value)
+    FUNC_LEAVE_NOAPI_VOID
 } /* end H5S__hyper_rebuild() */
 
 
@@ -6320,7 +8837,386 @@ done:
     FUNC_LEAVE_NOAPI(ret_value)
 } /* end H5S__hyper_generate_spans() */
 
-#ifndef NEW_HYPERSLAB_API
+
+/*--------------------------------------------------------------------------
+ NAME
+    H5S__check_spans_overlap
+ PURPOSE
+    Check if two selections' bounds overlap.
+ USAGE
+    hbool_t H5S__check_spans_overlap(spans1, spans2)
+        const H5S_hyper_span_info_t *spans1;  IN: Second span list
+        const H5S_hyper_span_info_t *spans2;  IN: Second span list
+ RETURNS
+    TRUE for overlap, FALSE for no overlap
+ PROGRAMMER
+    Quincey Koziol -  January 24, 2019
+ GLOBAL VARIABLES
+ COMMENTS, BUGS, ASSUMPTIONS
+ EXAMPLES
+ REVISION LOG
+--------------------------------------------------------------------------*/
+static H5_ATTR_PURE hbool_t
+H5S__check_spans_overlap(const H5S_hyper_span_info_t *spans1,
+    const H5S_hyper_span_info_t *spans2)
+{
+    hbool_t ret_value = FALSE;          /* Return value */
+
+    FUNC_ENTER_STATIC_NOERR
+
+    /* Sanity checks */
+    HDassert(spans1);
+    HDassert(spans2);
+
+    /* Use low & high bounds to try to avoid spinning through the span lists */
+    if(H5S_RANGE_OVERLAP(spans1->low_bounds[0], spans1->high_bounds[0],
+                spans2->low_bounds[0], spans2->high_bounds[0])) {
+        H5S_hyper_span_t *span1, *span2;    /* Hyperslab spans */
+
+        /* Walk over spans, comparing them for overlap */
+        span1 = spans1->head;
+        span2 = spans2->head;
+        while(span1 && span2) {
+            /* Check current two spans for overlap */
+            if(H5S_RANGE_OVERLAP(span1->low, span1->high, span2->low, span2->high)) {
+                /* Check for spans in lowest dimension already */
+                if(span1->down) {
+                    /* Sanity check */
+                    HDassert(span2->down);
+
+                    /* Check lower dimensions for overlap */
+                    if(H5S__check_spans_overlap(span1->down, span2->down))
+                        HGOTO_DONE(TRUE);
+                } /* end if */
+                else
+                    HGOTO_DONE(TRUE);
+            } /* end if */
+
+            /* Advance one of the spans */
+            if(span1->high <= span2->high) {
+                /* Advance span1, unless it would be off the list and span2 has more nodes */
+                if(NULL == span1->next && NULL != span2->next)
+                    span2 = span2->next;
+                else
+                    span1 = span1->next;
+            } /* end if */
+            else {
+                /* Advance span2, unless it would be off the list and span1 has more nodes */
+                if(NULL == span2->next && NULL != span1->next)
+                    span1 = span1->next;
+                else
+                    span2 = span2->next;
+            } /* end else */
+        } /* end while */
+
+        /* Make certain we've exhausted our comparisons */
+        HDassert((NULL == span1 && (NULL != span2 && NULL == span2->next)) ||
+                ((NULL != span1 && NULL == span1->next) && NULL == span2));
+    } /* end of */
+
+done:
+    FUNC_LEAVE_NOAPI(ret_value)
+} /* end H5S__check_spans_overlap() */
+
+
+/*--------------------------------------------------------------------------
+ NAME
+    H5S__fill_in_new_space
+ PURPOSE
+    Combine two span lists, one from an existing dataspace and the
+    other from input arguments, into a new selection depending on the
+    selection operator. The new selection is put into a resulting dataspace
+    which could be allocated inside the function.
+ USAGE
+    herr_t H5S__fill_in_new_space(space1, op, space2_span_lst, can_own_span2,
+                                span2_owned, result)
+        H5S_t *space1;           IN: Dataspace containing the first span list
+        H5S_seloper_t op;        IN: Selection operation
+        H5S_hyper_span_info_t *space2_span_lst; IN: Second span list
+        hbool_t can_own_span2;   IN: Indicates whether the 2nd span list could be
+                                     owned by the result. If not, the 2nd span list
+                                     has to be copied.
+        hbool_t *span2_owned;  OUT: Indicates if the 2nd span list is actually owned
+        H5S_t **result;  OUT: The dataspace containing the the new selection. It
+                              could be same with the 1st dataspace.
+ RETURNS
+    Non-negative on success, negative on failure
+ PROGRAMMER
+    Chao Mei July 8, 2011
+ GLOBAL VARIABLES
+ COMMENTS, BUGS, ASSUMPTIONS
+ EXAMPLES
+ REVISION LOG
+--------------------------------------------------------------------------*/
+static herr_t
+H5S__fill_in_new_space(H5S_t *space1, H5S_seloper_t op,
+    H5S_hyper_span_info_t *space2_span_lst, hbool_t can_own_span2,
+    hbool_t *span2_owned, hbool_t *updated_spans, H5S_t **result)
+{
+    H5S_hyper_span_info_t *a_not_b = NULL;      /* Span tree for hyperslab spans in old span tree and not in new span tree */
+    H5S_hyper_span_info_t *a_and_b = NULL;      /* Span tree for hyperslab spans in both old and new span trees */
+    H5S_hyper_span_info_t *b_not_a = NULL;      /* Span tree for hyperslab spans in new span tree and not in old span tree */
+    hbool_t overlapped = FALSE;                 /* Whether selections overlap */
+    hbool_t is_result_new = FALSE;
+    herr_t ret_value = SUCCEED;         /* Return value */
+
+    FUNC_ENTER_STATIC
+
+    HDassert(space1);
+    HDassert(space2_span_lst);
+    HDassert(op >= H5S_SELECT_OR && op <= H5S_SELECT_NOTA);
+    /* The result is either a to-be-created space or an empty one */
+    HDassert(*result == NULL || *result == space1);
+    HDassert(space1->select.sel_info.hslab->span_lst);
+    HDassert(span2_owned);
+
+    /* Reset flags to return */
+    *span2_owned = FALSE;
+    *updated_spans = FALSE;
+
+    /* The result shares the same info from space1 */
+    if(*result == NULL) {
+        if(NULL == ((*result) = H5S_copy(space1, TRUE, TRUE)))
+            HGOTO_ERROR(H5E_DATASPACE, H5E_CANTINIT, FAIL, "unable to copy dataspace")
+        space1->select.sel_info.hslab->span_lst->count--;
+        (*result)->select.sel_info.hslab->span_lst = NULL;
+        is_result_new = TRUE;
+    } /* end if */
+
+    /* Check both spaces to see if they overlap */
+    overlapped = H5S__check_spans_overlap(space1->select.sel_info.hslab->span_lst, space2_span_lst);
+
+    if(!overlapped) {
+        switch(op) {
+            case H5S_SELECT_OR:
+            case H5S_SELECT_XOR:
+                /* Add the new disjoint spans to the space */
+                /* Copy of space1's spans to *result, and another copy of space2's spans */
+                if(is_result_new)
+                    (*result)->select.sel_info.hslab->span_lst = H5S__hyper_copy_span(space1->select.sel_info.hslab->span_lst, space1->extent.rank);
+                if(!can_own_span2) {
+                    b_not_a = H5S__hyper_copy_span(space2_span_lst, space1->extent.rank);
+                    if(H5S__hyper_add_disjoint_spans(*result, b_not_a) < 0)
+                        HGOTO_ERROR(H5E_DATASPACE, H5E_CANTINSERT, FAIL, "can't append hyperslabs")
+
+                    /* The new_spans are now owned by 'space', so they should not be released */
+                    b_not_a = NULL;
+                } /* end if */
+                else {
+                    if(H5S__hyper_add_disjoint_spans(*result, space2_span_lst) < 0)
+                        HGOTO_ERROR(H5E_DATASPACE, H5E_CANTINSERT, FAIL, "can't append hyperslabs")
+                    *span2_owned = TRUE;
+                } /* end else */
+
+                /* Indicate that the spans changed */
+                *updated_spans = TRUE;
+                break;
+
+            case H5S_SELECT_AND:
+                /* Convert *result to "none" selection */
+                if(H5S_select_none(*result) < 0)
+                    HGOTO_ERROR(H5E_DATASPACE, H5E_CANTSELECT, FAIL, "can't convert selection")
+                HGOTO_DONE(SUCCEED);
+
+            case H5S_SELECT_NOTB:
+                /* Copy space1's spans to *result */
+                if(is_result_new)
+                    (*result)->select.sel_info.hslab->span_lst = H5S__hyper_copy_span(space1->select.sel_info.hslab->span_lst, space1->extent.rank);
+
+                /* Indicate that the spans changed */
+                *updated_spans = TRUE;
+                break;
+
+            case H5S_SELECT_NOTA:
+                if(!is_result_new) {
+                    HDassert(space1 == *result);
+
+                    /* Free the current selection */
+                    H5S__hyper_free_span_info(space1->select.sel_info.hslab->span_lst);
+                    space1->select.sel_info.hslab->span_lst = NULL;
+                } /* end if */
+
+                /* Copy space2's spans to *result */
+                if(!can_own_span2)
+                    (*result)->select.sel_info.hslab->span_lst = H5S__hyper_copy_span(space2_span_lst, space1->extent.rank);
+                else {
+                    (*result)->select.sel_info.hslab->span_lst = space2_span_lst;
+                    *span2_owned = TRUE;
+                } /* end else */
+
+                /* Reset the number of items in selection */
+                (*result)->select.num_elem = H5S__hyper_spans_nelem(space2_span_lst);
+
+                /* Indicate that the spans changed */
+                *updated_spans = TRUE;
+                break;
+
+            case H5S_SELECT_NOOP:
+            case H5S_SELECT_SET:
+            case H5S_SELECT_APPEND:
+            case H5S_SELECT_PREPEND:
+            case H5S_SELECT_INVALID:
+            default:
+                HGOTO_ERROR(H5E_ARGS, H5E_UNSUPPORTED, FAIL, "invalid selection operation")
+        } /* end switch */
+    } /* end if */
+    else {
+        unsigned selector = 0;                  /* Select which clipping spans to generate */
+
+        /* Generate mask for clip operation depending on the op */
+        switch(op) {
+            case H5S_SELECT_OR: /* a + b_not_a */
+                selector = H5S_HYPER_COMPUTE_B_NOT_A;
+                break;
+
+            case H5S_SELECT_XOR: /* a_not_b + b_not_a */
+                selector = H5S_HYPER_COMPUTE_A_NOT_B | H5S_HYPER_COMPUTE_B_NOT_A;
+                break;
+
+            case H5S_SELECT_AND: /* a_and_b */
+                selector = H5S_HYPER_COMPUTE_A_AND_B;
+                break;
+
+            case H5S_SELECT_NOTB: /* a_not_b */
+                selector = H5S_HYPER_COMPUTE_A_NOT_B;
+                break;
+
+            case H5S_SELECT_NOTA: /* b_not_a */
+                selector = H5S_HYPER_COMPUTE_B_NOT_A;
+                break;
+
+            case H5S_SELECT_NOOP:
+            case H5S_SELECT_SET:
+            case H5S_SELECT_APPEND:
+            case H5S_SELECT_PREPEND:
+            case H5S_SELECT_INVALID:
+            default:
+                HGOTO_ERROR(H5E_ARGS, H5E_UNSUPPORTED, FAIL, "invalid selection operation")
+        } /* end switch */
+
+        /* Generate lists of spans which overlap and don't overlap */
+        if(H5S__hyper_clip_spans(space1->select.sel_info.hslab->span_lst,
+                space2_span_lst, selector, space1->extent.rank,
+                &a_not_b, &a_and_b, &b_not_a) < 0)
+            HGOTO_ERROR(H5E_DATASPACE, H5E_CANTCLIP, FAIL, "can't clip hyperslab information")
+        switch(op) {
+            case H5S_SELECT_OR:
+                if(is_result_new)
+                    (*result)->select.sel_info.hslab->span_lst = H5S__hyper_copy_span(space1->select.sel_info.hslab->span_lst, space1->extent.rank);
+                break;
+
+            case H5S_SELECT_AND:
+            case H5S_SELECT_XOR:
+            case H5S_SELECT_NOTB:
+            case H5S_SELECT_NOTA:
+                if(!is_result_new) {
+                    HDassert(space1 == *result);
+
+                    /* Free the current selection */
+                    H5S__hyper_free_span_info(space1->select.sel_info.hslab->span_lst);
+                    space1->select.sel_info.hslab->span_lst = NULL;
+                } /* end if */
+
+                /* Reset the number of items in selection */
+                /* (Will be set below) */
+                (*result)->select.num_elem = 0;
+                break;
+
+            case H5S_SELECT_NOOP:
+            case H5S_SELECT_SET:
+            case H5S_SELECT_APPEND:
+            case H5S_SELECT_PREPEND:
+            case H5S_SELECT_INVALID:
+            default:
+                HGOTO_ERROR(H5E_ARGS, H5E_UNSUPPORTED, FAIL, "invalid selection operation")
+        } /* end switch */
+
+        /* Check if there are any non-overlapped selections */
+        if(a_not_b) {
+            /* Other than OR, the span_lst is set to NULL. And in OR,
+             *      a_not_b is not needed
+             */
+            HDassert(NULL == (*result)->select.sel_info.hslab->span_lst);
+
+            /* The results dataspace takes ownership of the spans */
+            /* (Since it must be NULL) */
+            (*result)->select.sel_info.hslab->span_lst = a_not_b;
+
+            /* Update the number of elements in current selection */
+            (*result)->select.num_elem = H5S__hyper_spans_nelem(a_not_b);
+
+            /* Indicate that the spans were updated */
+            *updated_spans = TRUE;
+
+            /* Indicate that the a_not_b spans are owned */
+            a_not_b = NULL;
+        } /* end if */
+
+        if(a_and_b) {
+            /**
+             * 1. Other than OR, the span_lst is set to NULL. And in OR,
+             *      a_and_b is not needed
+             * 2. a_not_b will never be computed together with a_and_b
+             *      because merging these two equals to a.
+             */
+            HDassert(NULL == (*result)->select.sel_info.hslab->span_lst);
+
+            /* The results dataspace takes ownership of the spans */
+            /* (Since it must be NULL) */
+            (*result)->select.sel_info.hslab->span_lst = a_and_b;
+
+            /* Update the number of elements in current selection */
+            (*result)->select.num_elem = H5S__hyper_spans_nelem(a_and_b);
+
+            /* Indicate that the spans were updated */
+            *updated_spans = TRUE;
+
+            /* Indicate that the a_and_b spans are owned */
+            a_and_b = NULL;
+        } /* end if */
+
+        if(b_not_a) {
+            /* Merge the b_not_a spans into the result dataspace */
+            if(H5S__hyper_merge_spans(*result, b_not_a) < 0)
+                HGOTO_ERROR(H5E_DATASPACE, H5E_CANTINSERT, FAIL, "can't insert hyperslabs")
+
+            /* Update the number of elements in current selection */
+            (*result)->select.num_elem += H5S__hyper_spans_nelem(b_not_a);
+
+            /* Indicate that the spans were updated */
+            *updated_spans = TRUE;
+        } /* end if */
+    } /* end else for the case the new span overlaps with the old (i.e. space) */
+
+    /* Check if the spans weren't updated, and reset selection if so */
+    if(!*updated_spans) {
+        /* If updated_spans remains FALSE as in this branch, it means the
+         *  result has been cleared in XOR / AND / NOTB / NOTA cases, and the
+         *  result is a copy of the dataspace in the OR case.
+         *
+         *  If two dataspaces have generated any of the three clipped
+         *  span trees (i.e. a_not_b, a_and_b, and b_not_a), the
+         *  updated_spans must be TRUE.
+         */
+        if(H5S_SELECT_OR != op) {
+            /* Convert *result to "none" selection */
+            if(H5S_select_none(*result) < 0)
+                HGOTO_ERROR(H5E_DATASPACE, H5E_CANTSELECT, FAIL, "can't convert selection")
+        } /* end else */
+    } /* end if */
+
+done:
+    /* Free resources */
+    if(a_not_b)
+        H5S__hyper_free_span_info(a_not_b);
+    if(a_and_b)
+        H5S__hyper_free_span_info(a_and_b);
+    if(b_not_a)
+        H5S__hyper_free_span_info(b_not_a);
+
+    FUNC_LEAVE_NOAPI(ret_value)
+} /* end H5S__fill_in_new_space() */
+
 
 /*-------------------------------------------------------------------------
  * Function:    H5S__generate_hyperlab
@@ -6339,9 +9235,6 @@ H5S__generate_hyperslab(H5S_t *space, H5S_seloper_t op, const hsize_t start[],
     const hsize_t stride[], const hsize_t count[], const hsize_t block[])
 {
     H5S_hyper_span_info_t *new_spans = NULL;    /* Span tree for new hyperslab */
-    H5S_hyper_span_info_t *a_not_b = NULL;      /* Span tree for hyperslab spans in old span tree and not in new span tree */
-    H5S_hyper_span_info_t *a_and_b = NULL;      /* Span tree for hyperslab spans in both old and new span trees */
-    H5S_hyper_span_info_t *b_not_a = NULL;      /* Span tree for hyperslab spans in new span tree and not in old span tree */
     herr_t ret_value = SUCCEED;         /* Return value */
 
     FUNC_ENTER_STATIC
@@ -6360,9 +9253,12 @@ H5S__generate_hyperslab(H5S_t *space, H5S_seloper_t op, const hsize_t start[],
 
     /* Generate list of blocks to add/remove based on selection operation */
     if(op == H5S_SELECT_SET) {
-        /* Add new spans to current selection */
-        if(H5S__hyper_merge_spans(space,new_spans,TRUE)<0)
-            HGOTO_ERROR(H5E_DATASPACE, H5E_CANTINSERT, FAIL, "can't insert hyperslabs")
+        /* Free current selection */
+        if(NULL != space->select.sel_info.hslab->span_lst)
+            H5S__hyper_free_span_info(space->select.sel_info.hslab->span_lst);
+
+        /* Set the hyperslab selection to the new span tree */
+        space->select.sel_info.hslab->span_lst = new_spans;
 
         /* Set the number of elements in current selection */
         space->select.num_elem = H5S__hyper_spans_nelem(new_spans);
@@ -6371,194 +9267,375 @@ H5S__generate_hyperslab(H5S_t *space, H5S_seloper_t op, const hsize_t start[],
         new_spans = NULL;
     } /* end if */
     else {
+        hbool_t new_spans_owned = FALSE;
         hbool_t updated_spans = FALSE;
 
-        /* Generate lists of spans which overlap and don't overlap */
-        if(H5S__hyper_clip_spans(space->select.sel_info.hslab->span_lst,new_spans,&a_not_b,&a_and_b,&b_not_a)<0)
-            HGOTO_ERROR(H5E_DATASPACE, H5E_CANTCLIP, FAIL, "can't clip hyperslab information")
+        /* Generate new spans for space */
+        if(H5S__fill_in_new_space(space, op, new_spans, TRUE, &new_spans_owned, &updated_spans, &space) < 0)
+            HGOTO_ERROR(H5E_DATASPACE, H5E_CANTSELECT, FAIL, "can't generate the specified hyperslab")
 
-        switch(op) {
-            case H5S_SELECT_OR:
-                /* Add any new spans from b_not_a to current selection */
-                if(b_not_a!=NULL) {
-                    if(H5S__hyper_merge_spans(space,b_not_a,FALSE)<0)
-                        HGOTO_ERROR(H5E_DATASPACE, H5E_CANTINSERT, FAIL, "can't insert hyperslabs")
+        /* Check if the spans were updated by H5S__fill_in_new_space */
+        if(updated_spans) {
+            H5S_hyper_dim_t new_hyper_diminfo[H5S_MAX_RANK];
+            unsigned u;                         /* Local index variable */
 
-                    /* Update the number of elements in current selection */
-                    space->select.num_elem += H5S__hyper_spans_nelem(b_not_a);
+            /* Sanity check */
+            HDassert(space->select.sel_info.hslab->span_lst->head);
+
+            /* Build diminfo struct */
+            for(u = 0; u <space->extent.rank; u++) {
+                new_hyper_diminfo[u].start = start[u];
+                new_hyper_diminfo[u].stride = stride[u];
+                new_hyper_diminfo[u].count = count[u];
+                new_hyper_diminfo[u].block = block[u];
+            } /* end for */
 
-                    /* Indicate that the spans were updated */
-                    updated_spans = TRUE;
-                } /* end if */
-                break;
+            /* Update space's dim info */
+            if(H5S__hyper_update_diminfo(space, op, new_hyper_diminfo) < 0)
+                HGOTO_ERROR(H5E_DATASPACE, H5E_CANTCOUNT, FAIL, "can't update hyperslab info")
+        } /* end if */
 
-            case H5S_SELECT_AND:
-                /* Free the current selection */
-                if(H5S__hyper_free_span_info(space->select.sel_info.hslab->span_lst)<0)
-                    HGOTO_ERROR(H5E_INTERNAL, H5E_CANTFREE, FAIL, "failed to release hyperslab spans")
-                space->select.sel_info.hslab->span_lst=NULL;
+        /* Indicate that the new_spans are owned, there's no need to free */
+        if(new_spans_owned)
+            new_spans = NULL;
+    } /* end else */
 
-                /* Reset the number of items in selection */
-                space->select.num_elem=0;
+done:
+    if(new_spans)
+        H5S__hyper_free_span_info(new_spans);
 
-                /* Check if there are any overlapped selections */
-                if(a_and_b!=NULL) {
-                    if(H5S__hyper_merge_spans(space,a_and_b,TRUE)<0)
-                        HGOTO_ERROR(H5E_DATASPACE, H5E_CANTINSERT, FAIL, "can't insert hyperslabs")
+    FUNC_LEAVE_NOAPI(ret_value)
+} /* end H5S__generate_hyperslab() */
 
-                    /* Update the number of elements in current selection */
-                    space->select.num_elem = H5S__hyper_spans_nelem(a_and_b);
+
+/*-------------------------------------------------------------------------
+ * Function:    H5S__set_regular_hyperslab
+ *
+ * Purpose:    Set a regular hyperslab
+ *
+ * Return:    Non-negative on success/Negative on failure
+ *
+ * Programmer:    Quincey Koziol
+ *              Thursday, October 2, 2014
+ *
+ *-------------------------------------------------------------------------
+ */
+herr_t
+H5S__set_regular_hyperslab(H5S_t *space, const hsize_t start[],
+    const hsize_t *app_stride, const hsize_t app_count[], const hsize_t *app_block,
+    const hsize_t *opt_stride, const hsize_t opt_count[], const hsize_t *opt_block)
+{
+    unsigned u;                         /* Local index variable */
+    herr_t ret_value = SUCCEED;         /* Return value */
 
-                    /* Indicate that the a_and_b spans are owned */
-                    a_and_b=NULL;
+    FUNC_ENTER_STATIC
 
-                    /* Indicate that the spans were updated */
-                    updated_spans = TRUE;
-                } /* end if */
-                break;
+    /* Check args */
+    HDassert(space);
+    HDassert(start);
+    HDassert(app_stride);
+    HDassert(app_count);
+    HDassert(app_block);
+    HDassert(opt_stride);
+    HDassert(opt_count);
+    HDassert(opt_block);
+
+    /* If we are setting a new selection, remove current selection first */
+    if(H5S_SELECT_RELEASE(space) < 0)
+        HGOTO_ERROR(H5E_DATASPACE, H5E_CANTDELETE, FAIL, "can't release selection")
 
-            case H5S_SELECT_XOR:
-                /* Free the current selection */
-                if(H5S__hyper_free_span_info(space->select.sel_info.hslab->span_lst)<0)
-                    HGOTO_ERROR(H5E_INTERNAL, H5E_CANTFREE, FAIL, "failed to release hyperslab spans")
-                space->select.sel_info.hslab->span_lst=NULL;
+    /* Allocate space for the hyperslab selection information */
+    if(NULL == (space->select.sel_info.hslab = H5FL_MALLOC(H5S_hyper_sel_t)))
+        HGOTO_ERROR(H5E_DATASPACE, H5E_CANTALLOC, FAIL, "can't allocate hyperslab info")
 
-                /* Reset the number of items in selection */
-                space->select.num_elem=0;
+    /* Set the diminfo */
+    space->select.num_elem = 1;
+    space->select.sel_info.hslab->unlim_dim = -1;
+    for(u = 0; u < space->extent.rank; u++) {
+        /* Set application and optimized hyperslab info */
+        space->select.sel_info.hslab->diminfo.app[u].start = start[u];
+        space->select.sel_info.hslab->diminfo.app[u].stride = app_stride[u];
+        space->select.sel_info.hslab->diminfo.app[u].count = app_count[u];
+        space->select.sel_info.hslab->diminfo.app[u].block = app_block[u];
+
+        space->select.sel_info.hslab->diminfo.opt[u].start = start[u];
+        space->select.sel_info.hslab->diminfo.opt[u].stride = opt_stride[u];
+        space->select.sel_info.hslab->diminfo.opt[u].count = opt_count[u];
+        space->select.sel_info.hslab->diminfo.opt[u].block = opt_block[u];
+
+        /* Update # of elements selected */
+        space->select.num_elem *= (opt_count[u] * opt_block[u]);
+
+        /* Set low bound of bounding box for the hyperslab selection */
+        space->select.sel_info.hslab->diminfo.low_bounds[u] = start[u];
+
+        /* Check for unlimited dimension & set high bound */
+        if((app_count[u] == H5S_UNLIMITED) || (app_block[u] == H5S_UNLIMITED)) {
+            space->select.sel_info.hslab->unlim_dim = (int)u;
+            space->select.sel_info.hslab->diminfo.high_bounds[u] = H5S_UNLIMITED;
+        } /* end if */
+        else
+            space->select.sel_info.hslab->diminfo.high_bounds[u] = start[u] + opt_stride[u] * (opt_count[u] - 1) + (opt_block[u] - 1);
+    } /* end for */
 
-                /* Check if there are any non-overlapped selections */
-                if(a_not_b!=NULL) {
-                    if(H5S__hyper_merge_spans(space,a_not_b,FALSE)<0)
-                        HGOTO_ERROR(H5E_DATASPACE, H5E_CANTINSERT, FAIL, "can't insert hyperslabs")
+    /* Handle unlimited selections */
+    if(space->select.sel_info.hslab->unlim_dim >= 0) {
+        /* Calculate num_elem_non_unlim */
+        space->select.sel_info.hslab->num_elem_non_unlim = (hsize_t)1;
+        for(u = 0; u < space->extent.rank; u++)
+            if((int)u != space->select.sel_info.hslab->unlim_dim)
+                space->select.sel_info.hslab->num_elem_non_unlim *= (opt_count[u] * opt_block[u]);
 
-                    /* Update the number of elements in current selection */
-                    space->select.num_elem = H5S__hyper_spans_nelem(a_not_b);
+        /* Update num_elem */
+        space->select.num_elem = H5S_UNLIMITED;
+    } /* end if */
 
-                    /* Indicate that the spans were updated */
-                    updated_spans = TRUE;
-                } /* end if */
-                if(b_not_a!=NULL) {
-                    if(H5S__hyper_merge_spans(space,b_not_a,FALSE)<0)
-                        HGOTO_ERROR(H5E_DATASPACE, H5E_CANTINSERT, FAIL, "can't insert hyperslabs")
+    /* Indicate that the dimension information is valid */
+    space->select.sel_info.hslab->diminfo_valid = H5S_DIMINFO_VALID_YES;
 
-                    /* Update the number of elements in current selection */
-                    space->select.num_elem += H5S__hyper_spans_nelem(b_not_a);
+    /* Indicate that there's no slab information */
+    space->select.sel_info.hslab->span_lst = NULL;
 
-                    /* Indicate that the spans were updated */
-                    updated_spans = TRUE;
-                } /* end if */
-                break;
+    /* Set selection type */
+    space->select.type = H5S_sel_hyper;
 
-            case H5S_SELECT_NOTB:
-                /* Free the current selection */
-                if(H5S__hyper_free_span_info(space->select.sel_info.hslab->span_lst)<0)
-                    HGOTO_ERROR(H5E_INTERNAL, H5E_CANTFREE, FAIL, "failed to release hyperslab spans")
-                space->select.sel_info.hslab->span_lst=NULL;
+done:
+    FUNC_LEAVE_NOAPI(ret_value)
+} /* end H5S__set_regular_hyperslab() */
 
-                /* Reset the number of items in selection */
-                space->select.num_elem=0;
 
-                /* Check if there are any non-overlapped selections */
-                if(a_not_b!=NULL) {
-                    if(H5S__hyper_merge_spans(space,a_not_b,TRUE)<0)
-                        HGOTO_ERROR(H5E_DATASPACE, H5E_CANTINSERT, FAIL, "can't insert hyperslabs")
+/*-------------------------------------------------------------------------
+ * Function:    H5S__hyper_regular_and_single_block
+ *
+ * Purpose:    Optimized routine to perform "AND" operation of a single
+ *        block against a regular hyperslab selection.
+ *
+ * Note:    This algorithm is invoked when constructing the chunk map
+ *              and a regular hyperslab is selected in the file's dataspace.
+ *
+ * Return:    Non-negative on success / Negative on failure
+ *
+ * Programmer:    Quincey Koziol
+ *              Saturday, February 9, 2019
+ *
+ *-------------------------------------------------------------------------
+ */
+static herr_t
+H5S__hyper_regular_and_single_block(H5S_t *space, const hsize_t start[],
+    const hsize_t block[])
+{
+    hsize_t select_end, block_end;      /* End of block & selection */
+    hbool_t single_block;       /* Whether the selection is a single block */
+    hbool_t overlap;            /* Whether block & selection overlap */
+    unsigned u;                 /* Local index variable */
+    herr_t ret_value = SUCCEED; /* Return value */
 
-                    /* Update the number of elements in current selection */
-                    space->select.num_elem = H5S__hyper_spans_nelem(a_not_b);
+    FUNC_ENTER_NOAPI(FAIL)
 
-                    /* Indicate that the a_not_b are owned */
-                    a_not_b=NULL;
+    /* Check args */
+    HDassert(space);
+    HDassert(start);
+    HDassert(block);
 
-                    /* Indicate that the spans were updated */
-                    updated_spans = TRUE;
-                } /* end if */
+    /* Check for single block selection in dataspace */
+    single_block = TRUE;
+    for(u = 0; u < space->extent.rank; u++)
+        if(1 != space->select.sel_info.hslab->diminfo.opt[u].count) {
+            single_block = FALSE;
+            break;
+        } /* end if */
+
+    /* Perform different optimizations, based on type of regular selection */
+    if(single_block) {
+        hsize_t new_start[H5S_MAX_RANK];        /* New starting coordinate */
+        hsize_t new_block[H5S_MAX_RANK];        /* New block size */
+
+        /* Check for overlap and compute new start offset & block sizes */
+        overlap = TRUE;
+        for(u = 0; u < space->extent.rank; u++) {
+            /* Compute the end of the selection & block in this dimension */
+            select_end = space->select.sel_info.hslab->diminfo.high_bounds[u];
+            block_end = (start[u] + block[u]) - 1;
+
+            /* Check for overlap */
+            if(!H5S_RANGE_OVERLAP(space->select.sel_info.hslab->diminfo.opt[u].start, select_end, start[u], block_end)) {
+                overlap = FALSE;
                 break;
+            } /* end if */
 
-            case H5S_SELECT_NOTA:
-                /* Free the current selection */
-                if(H5S__hyper_free_span_info(space->select.sel_info.hslab->span_lst)<0)
-                    HGOTO_ERROR(H5E_INTERNAL, H5E_CANTFREE, FAIL, "failed to release hyperslab spans")
-                space->select.sel_info.hslab->span_lst=NULL;
+            /* Set new start & block size in this dimension */
+            new_start[u] = MAX(space->select.sel_info.hslab->diminfo.opt[u].start, start[u]);
+            new_block[u] = (MIN(select_end, block_end) - new_start[u]) + 1;
+        } /* end for */
 
-                /* Reset the number of items in selection */
-                space->select.num_elem=0;
+        /* Check for overlap of selection & block */
+        if(overlap) {
+            /* Set selection to regular hyperslab */
+            if(H5S__set_regular_hyperslab(space, new_start, H5S_hyper_ones_g, H5S_hyper_ones_g, new_block,
+                    H5S_hyper_ones_g, H5S_hyper_ones_g, new_block) < 0)
+                HGOTO_ERROR(H5E_DATASPACE, H5E_CANTSET, FAIL, "can't set regular hyperslab selection")
+        } /* end if */
+        else
+            /* Selection & block don't overlap, set to "none" selection */
+            if(H5S_select_none(space) < 0)
+                HGOTO_ERROR(H5E_DATASPACE, H5E_CANTSELECT, FAIL, "can't convert selection")
+    } /* end if */
+    else {
+        hsize_t new_start[H5S_MAX_RANK]; /* New start for hyperslab selection */
+        hsize_t new_count[H5S_MAX_RANK]; /* New count for hyperslab selection */
+        hsize_t stride[H5S_MAX_RANK];   /* Stride for hyperslab selection */
+        hsize_t new_block[H5S_MAX_RANK]; /* New block for hyperslab selection */
+        hbool_t partial_first_span;     /* Whether first span in intersection is partial */
+        hbool_t partial_last_span;      /* Whether last span in intersection is partial */
+
+        /* Iterate over selection, checking for overlap and computing first / last
+         *      span that intersects with the block.
+         */
+        overlap = TRUE;
+        partial_first_span = FALSE;
+        partial_last_span = FALSE;
+        for(u = 0; u < space->extent.rank; u++) {
+            hsize_t first_span_start, first_span_end;   /* Start / end of first span */
+            hsize_t last_span_start, last_span_end;   /* Start / end of last span */
+            hsize_t nstride;    /* Number of strides into the selection */
+
+            /* Compute the end of the selection & block in this dimension */
+            select_end = space->select.sel_info.hslab->diminfo.high_bounds[u];
+            block_end = (start[u] + block[u]) - 1;
+
+            /* Check for overlap */
+            if(!H5S_RANGE_OVERLAP(space->select.sel_info.hslab->diminfo.opt[u].start, select_end, start[u], block_end)) {
+                overlap = FALSE;
+                break;
+            } /* end if */
 
-                /* Check if there are any non-overlapped selections */
-                if(b_not_a!=NULL) {
-                    if(H5S__hyper_merge_spans(space,b_not_a,TRUE)<0)
-                        HGOTO_ERROR(H5E_DATASPACE, H5E_CANTINSERT, FAIL, "can't insert hyperslabs")
+            /* Find first span that is before or overlaps with start of block */
+            if(space->select.sel_info.hslab->diminfo.opt[u].start >= start[u]) {
+                /* Calculate start & end of first span */
+                first_span_start = space->select.sel_info.hslab->diminfo.opt[u].start;
+                first_span_end = (first_span_start +
+                        space->select.sel_info.hslab->diminfo.opt[u].block) - 1;
 
-                    /* Update the number of elements in current selection */
-                    space->select.num_elem = H5S__hyper_spans_nelem(b_not_a);
+                /* Check if first span overlaps _end_ of block */
+                if(block_end >= first_span_start && block_end <= first_span_end)
+                    partial_first_span = TRUE;
+            } /* end if */
+            else {
+                hsize_t adj_start;  /* Start coord, adjusted for hyperslab selection parameters */
+
+                /* Adjust start coord for selection's 'start' offset */
+                adj_start = start[u] - space->select.sel_info.hslab->diminfo.opt[u].start;
+
+                /* Compute # of strides into the selection */
+                if(space->select.sel_info.hslab->diminfo.opt[u].count > 1)
+                    nstride = adj_start / space->select.sel_info.hslab->diminfo.opt[u].stride;
+                else
+                    nstride = 0;
 
-                    /* Indicate that the b_not_a are owned */
-                    b_not_a=NULL;
+                /* Calculate start & end of first span */
+                first_span_start = space->select.sel_info.hslab->diminfo.opt[u].start +
+                        (nstride * space->select.sel_info.hslab->diminfo.opt[u].stride);
+                first_span_end = (first_span_start +
+                        space->select.sel_info.hslab->diminfo.opt[u].block) - 1;
 
-                    /* Indicate that the spans were updated */
-                    updated_spans = TRUE;
+                /* Check if first span overlaps start of block */
+                if(first_span_start < start[u] && first_span_end >= start[u])
+                    partial_first_span = TRUE;
+
+                /* Advance first span to start higher than block's start,
+                 *      if it's not partial.
+                 */
+                if(first_span_end < start[u]) {
+                    first_span_start += space->select.sel_info.hslab->diminfo.opt[u].stride;
+                    first_span_end += space->select.sel_info.hslab->diminfo.opt[u].stride;
                 } /* end if */
-                break;
+            } /* end else */
 
-            case H5S_SELECT_NOOP:
-            case H5S_SELECT_SET:
-            case H5S_SELECT_APPEND:
-            case H5S_SELECT_PREPEND:
-            case H5S_SELECT_INVALID:
-            default:
-                HGOTO_ERROR(H5E_ARGS, H5E_UNSUPPORTED, FAIL, "invalid selection operation")
-        } /* end switch */
+            /* Find last span that is before or overlaps with end of block */
+            if(select_end < block_end) {
+                /* Calculate start & end of last span */
+                last_span_start = (select_end -
+                        space->select.sel_info.hslab->diminfo.opt[u].block) + 1;
+                last_span_end = select_end;
 
-        /* Check if the resulting hyperslab span tree is empty */
-        if(space->select.sel_info.hslab->span_lst==NULL) {
-            H5S_hyper_span_info_t *spans;     /* Empty hyperslab span tree */
+                /* Check if last span overlaps _start_ of block */
+                if(start[u] >= last_span_start && start[u] <= last_span_end)
+                    partial_last_span = TRUE;
+            } /* end if */
+            else {
+                hsize_t adj_end;    /* End coord, adjusted for hyperslab selection parameters */
+
+                /* Adjust end coord for selection's 'start' offset */
+                adj_end = block_end - space->select.sel_info.hslab->diminfo.opt[u].start;
+
+                /* Compute # of strides into the selection */
+                if(space->select.sel_info.hslab->diminfo.opt[u].count > 1)
+                    nstride = adj_end / space->select.sel_info.hslab->diminfo.opt[u].stride;
+                else
+                    nstride = 0;
+
+                /* Calculate start & end of last span */
+                last_span_start = space->select.sel_info.hslab->diminfo.opt[u].start +
+                        (nstride * space->select.sel_info.hslab->diminfo.opt[u].stride);
+                last_span_end = (last_span_start +
+                        space->select.sel_info.hslab->diminfo.opt[u].block) - 1;
+
+                /* Check if last span overlaps end of block */
+                if(block_end >= last_span_start && block_end <= last_span_end)
+                    partial_last_span = TRUE;
+            } /* end else */
+
+            /* Check if no spans are inside block */
+            /* (Can happen when block falls in "gap" between spans) */
+            if(last_span_end < start[u]) {
+                overlap = FALSE;
+                break;
+            } /* end if */
 
             /* Sanity check */
-            HDassert(space->select.num_elem == 0);
+            HDassert(first_span_start <= last_span_start);
 
-            /* Allocate a span info node */
-            if((spans = H5FL_MALLOC(H5S_hyper_span_info_t))==NULL)
-                HGOTO_ERROR(H5E_RESOURCE, H5E_NOSPACE, FAIL, "can't allocate hyperslab span")
+            /* Compute new start / count / block values */
+            new_start[u] = first_span_start;
+            if(last_span_start != first_span_start)
+                new_count[u] = ((last_span_start - first_span_start) /
+                        space->select.sel_info.hslab->diminfo.opt[u].stride) + 1;
+            else
+                new_count[u] = 1;
+            new_block[u] = space->select.sel_info.hslab->diminfo.opt[u].block;
 
-            /* Set the reference count */
-            spans->count=1;
+            /* Keep same stride */
+            stride[u] = space->select.sel_info.hslab->diminfo.opt[u].stride;
+        } /* end for */
 
-            /* Reset the scratch pad space */
-            spans->scratch=0;
+        /* Check for overlap of selection & block */
+        if(overlap) {
+            /* Set selection to regular hyperslab */
+            if(H5S__set_regular_hyperslab(space, new_start, stride, new_count, new_block,
+                    stride, new_count, new_block) < 0)
+                HGOTO_ERROR(H5E_DATASPACE, H5E_CANTSET, FAIL, "can't set regular hyperslab selection")
 
-            /* Set to empty tree */
-            spans->head=NULL;
+            /* If there's a partial first or last span, have to 'AND' against selection */
+            if(partial_first_span || partial_last_span) {
+                /* Generate span tree for regular selection */
+                if(H5S__hyper_generate_spans(space) < 0)
+                    HGOTO_ERROR(H5E_DATASPACE, H5E_UNINITIALIZED, FAIL, "dataspace does not have span tree")
 
-            /* Set pointer to empty span tree */
-            space->select.sel_info.hslab->span_lst=spans;
+                /* 'AND' against block */
+                if(H5S__generate_hyperslab(space, H5S_SELECT_AND, start, H5S_hyper_ones_g, H5S_hyper_ones_g, block) < 0)
+                    HGOTO_ERROR(H5E_DATASPACE, H5E_CANTINSERT, FAIL, "can't generate hyperslabs")
+            } /* end if */
         } /* end if */
         else {
-            /* Check if we updated the spans */
-            if(updated_spans) {
-                /* Attempt to rebuild "optimized" start/stride/count/block information.
-                 * from resulting hyperslab span tree
-                 */
-                H5S__hyper_rebuild(space);
-            } /* end if */
+            /* Selection & block don't overlap, set to "none" selection */
+            if(H5S_select_none(space) < 0)
+                HGOTO_ERROR(H5E_DATASPACE, H5E_CANTSELECT, FAIL, "can't convert selection")
         } /* end else */
     } /* end else */
 
 done:
-    /* Free resources */
-    if(a_not_b)
-        if(H5S__hyper_free_span_info(a_not_b) < 0)
-            HDONE_ERROR(H5E_INTERNAL, H5E_CANTFREE, FAIL, "failed to release temporary hyperslab spans")
-    if(a_and_b)
-        if(H5S__hyper_free_span_info(a_and_b) < 0)
-            HDONE_ERROR(H5E_INTERNAL, H5E_CANTFREE, FAIL, "failed to release temporary hyperslab spans")
-    if(b_not_a)
-        if(H5S__hyper_free_span_info(b_not_a) < 0)
-            HDONE_ERROR(H5E_INTERNAL, H5E_CANTFREE, FAIL, "failed to release temporary hyperslab spans")
-    if(new_spans)
-        if(H5S__hyper_free_span_info(new_spans) < 0)
-            HDONE_ERROR(H5E_INTERNAL, H5E_CANTFREE, FAIL, "failed to release temporary hyperslab spans")
-
     FUNC_LEAVE_NOAPI(ret_value)
-} /* end H5S__generate_hyperslab() */
+} /* end H5S__hyper_regular_and_single_block() */
 
 
 /*-------------------------------------------------------------------------
@@ -6798,56 +9875,13 @@ H5S_select_hyperslab(H5S_t *space, H5S_seloper_t op, const hsize_t start[],
     } /* end switch */
 
     if(op == H5S_SELECT_SET) {
-        /* If we are setting a new selection, remove current selection first */
-        if(H5S_SELECT_RELEASE(space) < 0)
-            HGOTO_ERROR(H5E_DATASPACE, H5E_CANTDELETE, FAIL, "can't release selection")
-
-        /* Allocate space for the hyperslab selection information */
-        if(NULL == (space->select.sel_info.hslab = H5FL_MALLOC(H5S_hyper_sel_t)))
-            HGOTO_ERROR(H5E_RESOURCE, H5E_NOSPACE, FAIL, "can't allocate hyperslab info")
-
-        /* Save the diminfo */
-        space->select.num_elem = 1;
-        for(u = 0; u < space->extent.rank; u++) {
-            space->select.sel_info.hslab->diminfo.app[u].start = start[u];
-            space->select.sel_info.hslab->diminfo.app[u].stride = stride[u];
-            space->select.sel_info.hslab->diminfo.app[u].count = count[u];
-            space->select.sel_info.hslab->diminfo.app[u].block = block[u];
-
-            space->select.sel_info.hslab->diminfo.opt[u].start = start[u];
-            space->select.sel_info.hslab->diminfo.opt[u].stride = opt_stride[u];
-            space->select.sel_info.hslab->diminfo.opt[u].count = opt_count[u];
-            space->select.sel_info.hslab->diminfo.opt[u].block = opt_block[u];
-
-            space->select.num_elem *= (opt_count[u] * opt_block[u]);
-        } /* end for */
-
-        /* Save unlim_dim */
-        space->select.sel_info.hslab->unlim_dim = unlim_dim;
-
-        /* Indicate that the dimension information is valid */
-        space->select.sel_info.hslab->diminfo_valid = H5S_DIMINFO_VALID_YES;
-
-        /* Indicate that there's no slab information */
-        space->select.sel_info.hslab->span_lst = NULL;
-
-        /* Handle unlimited selections */
-        if(unlim_dim >= 0) {
-            /* Calculate num_elem_non_unlim */
-            space->select.sel_info.hslab->num_elem_non_unlim = (hsize_t)1;
-            for(u = 0; u < space->extent.rank; u++)
-                if((int)u != unlim_dim)
-                    space->select.sel_info.hslab->num_elem_non_unlim *= (opt_count[u] * opt_block[u]);
-
-            /* Set num_elem */
-            if(space->select.num_elem != (hsize_t)0)
-                space->select.num_elem = H5S_UNLIMITED;
-        } /* end if */
-
-        /* Set selection type */
-        space->select.type = H5S_sel_hyper;
+        /* Set selection to regular hyperslab */
+        if(H5S__set_regular_hyperslab(space, start, stride, count, block, opt_stride, opt_count, opt_block) < 0)
+            HGOTO_ERROR(H5E_DATASPACE, H5E_CANTSET, FAIL, "can't set regular hyperslab selection")
     } /* end if */
     else if(op >= H5S_SELECT_OR && op <= H5S_SELECT_NOTA) {
+        hbool_t single_block;   /* Whether the selection is a single block */
+
         /* Sanity check */
         HDassert(H5S_GET_SELECT_TYPE(space) == H5S_SEL_HYPERSLABS);
 
@@ -6884,21 +9918,35 @@ H5S_select_hyperslab(H5S_t *space, H5S_seloper_t op, const hsize_t start[],
             } /* end if */
         } /* end if */
 
-        /* Check if there's no hyperslab span information currently */
-        if(NULL == space->select.sel_info.hslab->span_lst)
-            if(H5S__hyper_generate_spans(space) < 0)
-                HGOTO_ERROR(H5E_DATASPACE, H5E_UNINITIALIZED, FAIL, "dataspace does not have span tree")
+        /* Check for a single block selected */
+        single_block = TRUE;
+        for(u = 0; u < space->extent.rank; u++)
+            if(1 != opt_count[u]) {
+                single_block = FALSE;
+                break;
+            } /* end if */
 
-        /* Indicate that the regular dimensions are no longer valid */
-        space->select.sel_info.hslab->diminfo_valid = H5S_DIMINFO_VALID_NO;
+        /* Check for single block "AND" operation on a regular hyperslab, which
+         *      is used for constructing chunk maps and can be optimized for.
+         */
+        if(H5S_SELECT_AND == op && single_block &&
+                space->select.sel_info.hslab->diminfo_valid == H5S_DIMINFO_VALID_YES) {
+            if(H5S__hyper_regular_and_single_block(space, start, opt_block) < 0)
+                HGOTO_ERROR(H5E_DATASPACE, H5E_CANTOPERATE, FAIL, "can't 'AND' single block against regular hyperslab")
+        } /* end if */
+        else {
+            /* Check if there's no hyperslab span information currently */
+            if(NULL == space->select.sel_info.hslab->span_lst)
+                if(H5S__hyper_generate_spans(space) < 0)
+                    HGOTO_ERROR(H5E_DATASPACE, H5E_UNINITIALIZED, FAIL, "dataspace does not have span tree")
 
-        /* Set selection type */
-        /* (Could be overridden by resetting selection to 'none', below) */
-        space->select.type = H5S_sel_hyper;
+            /* Set selection type */
+            space->select.type = H5S_sel_hyper;
 
-        /* Add in the new hyperslab information */
-        if(H5S__generate_hyperslab(space, op, start, opt_stride, opt_count, opt_block) < 0)
-            HGOTO_ERROR(H5E_DATASPACE, H5E_CANTINSERT, FAIL, "can't generate hyperslabs")
+            /* Add in the new hyperslab information */
+            if(H5S__generate_hyperslab(space, op, start, opt_stride, opt_count, opt_block) < 0)
+                HGOTO_ERROR(H5E_DATASPACE, H5E_CANTINSERT, FAIL, "can't generate hyperslabs")
+        } /* end else */
     } /* end if */
     else
         HGOTO_ERROR(H5E_ARGS, H5E_UNSUPPORTED, FAIL, "invalid selection operation")
@@ -6970,690 +10018,265 @@ H5Sselect_hyperslab(hid_t space_id, H5S_seloper_t op, const hsize_t start[],
 done:
     FUNC_LEAVE_API(ret_value)
 } /* end H5Sselect_hyperslab() */
-#else /* NEW_HYPERSLAB_API */ /* Works */
-
-/*-------------------------------------------------------------------------
- * Function:	H5S_operate_hyperslab
- *
- * Purpose:	Combines two hyperslabs with an operation, putting the
- *              result into a third hyperslab selection
- *
- * Return:	non-negative on success/NULL on failure
- *
- * Programmer:	Quincey Koziol
- *              Tuesday, October 30, 2001
- *
- * Modifications:
- *
- *-------------------------------------------------------------------------
- */
-static herr_t
-H5S_operate_hyperslab (H5S_t *result, H5S_hyper_span_info_t *spans1, H5S_seloper_t op, H5S_hyper_span_info_t *spans2,
-    hbool_t can_own_span2, hbool_t *span2_owned)
-{
-    H5S_hyper_span_info_t *a_not_b=NULL;    /* Span tree for hyperslab spans in old span tree and not in new span tree */
-    H5S_hyper_span_info_t *a_and_b=NULL;    /* Span tree for hyperslab spans in both old and new span trees */
-    H5S_hyper_span_info_t *b_not_a=NULL;    /* Span tree for hyperslab spans in new span tree and not in old span tree */
-    herr_t      ret_value=SUCCEED;       /* Return value */
-
-    FUNC_ENTER_NOAPI_NOINIT
-
-    /* Check args */
-    HDassert(result);
-    HDassert(spans2);
-    HDassert(op > H5S_SELECT_NOOP && op < H5S_SELECT_INVALID);
-
-    /* Just copy the selection from spans2 if we are setting the selection */
-    /* ('space1' to 'result' aliasing happens at the next layer up) */
-    if(op==H5S_SELECT_SET) {
-        if(H5S__hyper_merge_spans(result,spans2,can_own_span2)<0)
-            HGOTO_ERROR(H5E_DATASPACE, H5E_CANTINSERT, FAIL, "can't insert hyperslabs")
-
-        /* Update the number of elements in current selection */
-        result->select.num_elem = H5S__hyper_spans_nelem(spans2);
-
-        /* Indicate that we took ownership of span2, if allowed */
-        if(can_own_span2)
-            *span2_owned=TRUE;
-    } /* end if */
-    else {
-        hbool_t updated_spans = FALSE;  /* Whether the spans in the selection were modified */
-
-        HDassert(spans1);
-
-        /* Generate lists of spans which overlap and don't overlap */
-        if(H5S__hyper_clip_spans(spans1,spans2,&a_not_b,&a_and_b,&b_not_a)<0)
-            HGOTO_ERROR(H5E_DATASPACE, H5E_CANTCLIP, FAIL, "can't clip hyperslab information")
-
-        /* Switch on the operation */
-        switch(op) {
-            case H5S_SELECT_OR:
-                /* Copy spans from spans1 to current selection */
-                if(spans1!=NULL) {
-                    if(H5S__hyper_merge_spans(result,spans1,FALSE)<0)
-                        HGOTO_ERROR(H5E_DATASPACE, H5E_CANTINSERT, FAIL, "can't insert hyperslabs")
-
-                    /* Update the number of elements in current selection */
-                    result->select.num_elem = H5S__hyper_spans_nelem(spans1);
-                } /* end if */
-
-                /* Add any new spans from spans2 to current selection */
-                if(b_not_a!=NULL) {
-                    if(H5S__hyper_merge_spans(result,b_not_a,FALSE)<0)
-                        HGOTO_ERROR(H5E_DATASPACE, H5E_CANTINSERT, FAIL, "can't insert hyperslabs")
-
-                    /* Update the number of elements in current selection */
-                    result->select.num_elem += H5S__hyper_spans_nelem(b_not_a);
-
-                    /* Indicate that the spans were updated */
-                    updated_spans = TRUE;
-                } /* end if */
-                break;
-
-            case H5S_SELECT_AND:
-                /* Check if there are any overlapped selections */
-                if(a_and_b!=NULL) {
-                    if(H5S__hyper_merge_spans(result,a_and_b,TRUE)<0)
-                        HGOTO_ERROR(H5E_DATASPACE, H5E_CANTINSERT, FAIL, "can't insert hyperslabs")
-
-                    /* Update the number of elements in current selection */
-                    result->select.num_elem = H5S__hyper_spans_nelem(a_and_b);
-
-                    /* Indicate that the result owns the a_and_b spans */
-                    a_and_b=NULL;
-
-                    /* Indicate that the spans were updated */
-                    updated_spans = TRUE;
-                } /* end if */
-                break;
-
-            case H5S_SELECT_XOR:
-                /* Check if there are any non-overlapped selections */
-                if(a_not_b!=NULL) {
-                    if(H5S__hyper_merge_spans(result,a_not_b,FALSE)<0)
-                        HGOTO_ERROR(H5E_DATASPACE, H5E_CANTINSERT, FAIL, "can't insert hyperslabs")
-
-                    /* Update the number of elements in current selection */
-                    result->select.num_elem = H5S__hyper_spans_nelem(a_not_b);
-
-                    /* Indicate that the spans were updated */
-                    updated_spans = TRUE;
-                } /* end if */
-                if(b_not_a!=NULL) {
-                    if(H5S__hyper_merge_spans(result,b_not_a,FALSE)<0)
-                        HGOTO_ERROR(H5E_DATASPACE, H5E_CANTINSERT, FAIL, "can't insert hyperslabs")
-
-                    /* Update the number of elements in current selection */
-                    result->select.num_elem += H5S__hyper_spans_nelem(b_not_a);
-
-                    /* Indicate that the spans were updated */
-                    updated_spans = TRUE;
-                } /* end if */
-                break;
-
-            case H5S_SELECT_NOTB:
-                /* Check if there are any non-overlapped selections */
-                if(a_not_b!=NULL) {
-                    if(H5S__hyper_merge_spans(result,a_not_b,TRUE)<0)
-                        HGOTO_ERROR(H5E_DATASPACE, H5E_CANTINSERT, FAIL, "can't insert hyperslabs")
-
-                    /* Update the number of elements in current selection */
-                    result->select.num_elem = H5S__hyper_spans_nelem(a_not_b);
-
-                    /* Indicate that the result owns the a_not_b spans */
-                    a_not_b=NULL;
-
-                    /* Indicate that the spans were updated */
-                    updated_spans = TRUE;
-                } /* end if */
-                break;
-
-            case H5S_SELECT_NOTA:
-                /* Check if there are any non-overlapped selections */
-                if(b_not_a!=NULL) {
-                    if(H5S__hyper_merge_spans(result,b_not_a,TRUE)<0)
-                        HGOTO_ERROR(H5E_DATASPACE, H5E_CANTINSERT, FAIL, "can't insert hyperslabs")
-
-                    /* Update the number of elements in current selection */
-                    result->select.num_elem = H5S__hyper_spans_nelem(b_not_a);
-
-                    /* Indicate that the result owns the b_not_a spans */
-                    b_not_a=NULL;
-
-                    /* Indicate that the spans were updated */
-                    updated_spans = TRUE;
-                } /* end if */
-                break;
-
-            default:
-                HGOTO_ERROR(H5E_ARGS, H5E_UNSUPPORTED, FAIL, "invalid selection operation")
-        } /* end switch */
-
-        /* Free the hyperslab trees generated from the clipping algorithm */
-        if(a_not_b)
-            H5S__hyper_free_span_info(a_not_b);
-        if(a_and_b)
-            H5S__hyper_free_span_info(a_and_b);
-        if(b_not_a)
-            H5S__hyper_free_span_info(b_not_a);
-
-        /* Check if the resulting hyperslab span tree is empty */
-        if(result->select.sel_info.hslab->span_lst==NULL) {
-            H5S_hyper_span_info_t *spans;     /* Empty hyperslab span tree */
-
-            /* Sanity check */
-            HDassert(result->select.num_elem == 0);
-
-            /* Allocate a span info node */
-            if((spans = H5FL_MALLOC(H5S_hyper_span_info_t))==NULL)
-                HGOTO_ERROR(H5E_RESOURCE, H5E_NOSPACE, NULL, "can't allocate hyperslab span")
-
-            /* Set the reference count */
-            spans->count=1;
-
-            /* Reset the scratch pad space */
-            spans->scratch=0;
-
-            /* Set to empty tree */
-            spans->head=NULL;
-
-            /* Set pointer to empty span tree */
-            result->select.sel_info.hslab->span_lst=spans;
-        } /* end if */
-        else {
-            /* Check if we updated the spans */
-            if(updated_spans) {
-                /* Attempt to rebuild "optimized" start/stride/count/block information.
-                 * from resulting hyperslab span tree
-                 */
-                H5S__hyper_rebuild(result);
-            } /* end if */
-        } /* end else */
-    } /* end else */
-
-done:
-    FUNC_LEAVE_NOAPI(ret_value)
-}   /* end H5S_operate_hyperslab() */
-
-
-/*-------------------------------------------------------------------------
- * Function:	H5S_generate_hyperlab
- *
- * Purpose:	Generate hyperslab information from H5S_select_hyperslab()
- *
- * Return:	Non-negative on success/Negative on failure
- *
- * Programmer:	Quincey Koziol (split from HS_select_hyperslab()).
- *              Tuesday, September 12, 2000
- *
- * Modifications:
- *
- *-------------------------------------------------------------------------
- */
-static herr_t
-H5S__generate_hyperslab(H5S_t *space, H5S_seloper_t op, const hsize_t start[],
-    const hsize_t stride[], const hsize_t count[], const hsize_t block[])
-{
-    H5S_hyper_span_info_t *new_spans=NULL;   /* Span tree for new hyperslab */
-    H5S_hyper_span_info_t *tmp_spans=NULL;   /* Temporary copy of selection */
-    hbool_t span2_owned=FALSE;          /* Flag to indicate that span2 was used in H5S_operate_hyperslab() */
-    herr_t      ret_value=SUCCEED;       /* Return value */
-
-    FUNC_ENTER_NOAPI_NOINIT
-
-    /* Check args */
-    HDassert(space);
-    HDassert(op > H5S_SELECT_NOOP && op < H5S_SELECT_INVALID);
-    HDassert(start);
-    HDassert(stride);
-    HDassert(count);
-    HDassert(block);
-
-    /* Generate span tree for new hyperslab information */
-    if(NULL == (new_spans = H5S__hyper_make_spans(space->extent.rank, start, stride, count, block)))
-        HGOTO_ERROR(H5E_DATASPACE, H5E_CANTINSERT, FAIL, "can't create hyperslab information")
-
-    /* Copy the original dataspace */
-    if(space->select.sel_info.hslab->span_lst!=NULL) {
-        /* Take ownership of the dataspace's hyperslab spans */
-        /* (These are freed later) */
-        tmp_spans=space->select.sel_info.hslab->span_lst;
-        space->select.sel_info.hslab->span_lst=NULL;
-
-        /* Reset the other dataspace selection information */
-        if(H5S_SELECT_RELEASE(space)<0)
-            HGOTO_ERROR(H5E_DATASPACE, H5E_CANTDELETE, FAIL, "can't release selection")
-
-        /* Allocate space for the hyperslab selection information */
-        if((space->select.sel_info.hslab=H5FL_MALLOC(H5S_hyper_sel_t))==NULL)
-            HGOTO_ERROR(H5E_RESOURCE, H5E_NOSPACE, FAIL, "can't allocate hyperslab info")
-
-        /* Set unlim_dim */
-        space->select.sel_info.hslab->unlim_dim = -1;
-    } /* end if */
-
-    /* Combine tmp_space (really space) & new_space, with the result in space */
-    if(H5S_operate_hyperslab(space,tmp_spans,op,new_spans,TRUE,&span2_owned)<0)
-        HGOTO_ERROR(H5E_DATASPACE, H5E_CANTCLIP, FAIL, "can't clip hyperslab information")
-
-done:
-    /* Free temporary data structures */
-    if(tmp_spans!=NULL)
-        if(H5S__hyper_free_span_info(tmp_spans)<0)
-            HDONE_ERROR(H5E_INTERNAL, H5E_CANTFREE, FAIL, "failed to release temporary hyperslab spans")
-    if(new_spans!=NULL && span2_owned==FALSE)
-        if(H5S__hyper_free_span_info(new_spans)<0)
-            HDONE_ERROR(H5E_INTERNAL, H5E_CANTFREE, FAIL, "failed to release temporary hyperslab spans")
-
-    FUNC_LEAVE_NOAPI(ret_value)
-} /* end H5S__generate_hyperslab() */
 
 
-/*-------------------------------------------------------------------------
- * Function:	H5S_select_hyperslab
- *
- * Purpose:	Internal version of H5Sselect_hyperslab().
- *
- * Return:	Non-negative on success/Negative on failure
- *
- * Programmer:	Quincey Koziol
- *              Wednesday, January 10, 2001
- *
- * Modifications:
- *
- *-------------------------------------------------------------------------
- */
+/*--------------------------------------------------------------------------
+ NAME
+    H5S_combine_hyperslab
+ PURPOSE
+    Specify a hyperslab to combine with the current hyperslab selection, and
+    store the result in the new hyperslab selection.
+ USAGE
+    herr_t H5S_combine_hyperslab(new_space, old_space, op, start, stride, count, block)
+        H5S_t *old_space;            IN: The old space the selection is performed on
+        H5S_seloper_t op;            IN: Operation to perform on current selection
+        const hsize_t start[];       IN: Offset of start of hyperslab
+        const hsize_t *stride;       IN: Hyperslab stride
+        const hsize_t count[];       IN: Number of blocks included in hyperslab
+        const hsize_t *block;        IN: Size of block in hyperslab
+        H5S_t **new_space;           OUT: The new dataspace to store the selection result
+ RETURNS
+    Non-negative on success/Negative on failure
+ DESCRIPTION
+    Combines a hyperslab selection with the current selection for a dataspace.
+    If STRIDE or BLOCK is NULL, they are assumed to be set to all '1'.
+ GLOBAL VARIABLES
+ COMMENTS, BUGS, ASSUMPTIONS
+    In some cases, copying the whole span tree from old_space to new_space
+    can be avoided.  Deal with such cases directly, otherwise this function
+    is equivalent to:
+        1. Copy the whole span tree from old_space into new_space
+        2. Call H5S_select_hyperslab with the new_space.
+ EXAMPLES
+ REVISION LOG
+--------------------------------------------------------------------------*/
 herr_t
-H5S_select_hyperslab (H5S_t *space, H5S_seloper_t op,
-		      const hsize_t start[],
-		      const hsize_t *stride,
-		      const hsize_t count[],
-		      const hsize_t *block)
+H5S_combine_hyperslab(H5S_t *old_space, H5S_seloper_t op, const hsize_t start[],
+    const hsize_t *stride, const hsize_t count[], const hsize_t *block,
+    H5S_t **new_space)
 {
-    hsize_t int_stride[H5S_MAX_RANK];   /* Internal storage for stride information */
-    hsize_t int_count[H5S_MAX_RANK];    /* Internal storage for count information */
-    hsize_t int_block[H5S_MAX_RANK];    /* Internal storage for block information */
-    const hsize_t *opt_stride;      /* Optimized stride information */
-    const hsize_t *opt_count;       /* Optimized count information */
-    const hsize_t *opt_block;       /* Optimized block information */
-    unsigned u;                    /* Counters */
-    int unlim_dim = -1;             /* Unlimited dimension in selection, of -1 if none */
-    herr_t      ret_value=SUCCEED;       /* Return value */
+    unsigned u;                     /* Local index variable */
+    herr_t ret_value = SUCCEED;     /* Return value */
 
     FUNC_ENTER_NOAPI(FAIL)
 
     /* Check args */
-    HDassert(space);
+    HDassert(old_space);
     HDassert(start);
     HDassert(count);
-    HDassert(op > H5S_SELECT_NOOP && op < H5S_SELECT_INVALID);
+    HDassert(op >= H5S_SELECT_SET && op <= H5S_SELECT_NOTA);
+    HDassert(new_space);
+    HDassert(*new_space == NULL);
 
     /* Point to the correct stride values */
-    if(stride==NULL)
+    if(stride == NULL)
         stride = H5S_hyper_ones_g;
 
     /* Point to the correct block values */
-    if(block==NULL)
+    if(block == NULL)
         block = H5S_hyper_ones_g;
 
-    /* Check for unlimited dimension */
-    for(u = 0; u<space->extent.rank; u++)
-        if((count[u] == H5S_UNLIMITED) || (block[u] == H5S_UNLIMITED)) {
-            if(unlim_dim >= 0)
-                HGOTO_ERROR(H5E_DATASPACE, H5E_UNSUPPORTED, FAIL, "cannot have more than one unlimited dimension in selection")
-            else {
-                if(count[u] == block[u] /* == H5S_UNLIMITED */)
-                    HGOTO_ERROR(H5E_DATASPACE, H5E_UNSUPPORTED, FAIL, "count and block cannot both be unlimited")
-                unlim_dim = (int)u;
-            } /* end else */
-        } /* end if */
-
-    /*
-     * Check new selection.
-     */
-    for(u=0; u<space->extent.rank; u++) {
+    /* Check new selection. */
+    for(u = 0; u < old_space->extent.rank; u++) {
         /* Check for overlapping hyperslab blocks in new selection. */
-        if(count[u]>1 && stride[u]<block[u])
+        if(count[u] > 1 && stride[u] < block[u])
             HGOTO_ERROR(H5E_ARGS, H5E_BADVALUE, FAIL, "hyperslab blocks overlap")
 
         /* Detect zero-sized hyperslabs in new selection */
         if(count[u] == 0 || block[u] == 0) {
             switch(op) {
-                case H5S_SELECT_SET:   /* Select "set" operation */
                 case H5S_SELECT_AND:   /* Binary "and" operation for hyperslabs */
                 case H5S_SELECT_NOTA:  /* Binary "B not A" operation for hyperslabs */
                     /* Convert to "none" selection */
-                    if(H5S_select_none(space)<0)
-                        HGOTO_ERROR(H5E_DATASPACE, H5E_CANTDELETE, FAIL, "can't convert selection")
+                    /* Copy the first dataspace without sharing the list of spans */
+                    if(NULL == ((*new_space) = H5S_copy(old_space, TRUE, TRUE)))
+                        HGOTO_ERROR(H5E_DATASPACE, H5E_CANTINIT, FAIL, "unable to copy dataspace")
+                    if(H5S_select_none((*new_space)) < 0)
+                        HGOTO_ERROR(H5E_DATASPACE, H5E_CANTSELECT, FAIL, "can't convert selection")
                     HGOTO_DONE(SUCCEED);
 
                 case H5S_SELECT_OR:    /* Binary "or" operation for hyperslabs */
                 case H5S_SELECT_XOR:   /* Binary "xor" operation for hyperslabs */
                 case H5S_SELECT_NOTB:  /* Binary "A not B" operation for hyperslabs */
+                    /* Copy the first dataspace with sharing the list of spans */
+                    if(NULL == ((*new_space) = H5S_copy(old_space, FALSE, TRUE)))
+                        HGOTO_ERROR(H5E_DATASPACE, H5E_CANTINIT, FAIL, "unable to copy dataspace")
                     HGOTO_DONE(SUCCEED);        /* Selection stays same */
 
+                case H5S_SELECT_NOOP:
+                case H5S_SELECT_SET:
+                case H5S_SELECT_APPEND:
+                case H5S_SELECT_PREPEND:
+                case H5S_SELECT_INVALID:
                 default:
                     HGOTO_ERROR(H5E_ARGS, H5E_UNSUPPORTED, FAIL, "invalid selection operation")
             } /* end switch */
         } /* end if */
     } /* end for */
 
-    /* Optimize hyperslab parameters to merge contiguous blocks, etc. */
-    if(stride == H5S_hyper_ones_g && block == H5S_hyper_ones_g) {
-        /* Point to existing arrays */
-        opt_stride = H5S_hyper_ones_g;
-        opt_count = H5S_hyper_ones_g;
-        opt_block = count;
-    } /* end if */
-    else {
-        /* Point to local arrays */
-        opt_stride = int_stride;
-        opt_count = int_count;
-        opt_block = int_block;
-        for(u=0; u<space->extent.rank; u++) {
-            /* contiguous hyperslabs have the block size equal to the stride */
-            if((stride[u] == block[u]) && (count[u] != H5S_UNLIMITED)) {
-                int_count[u]=1;
-                int_stride[u]=1;
-                if(block[u]==1)
-                    int_block[u]=count[u];
-                else
-                    int_block[u]=block[u]*count[u];
-            } /* end if */
-            else {
-                if(count[u]==1)
-                    int_stride[u]=1;
-                else {
-                    HDassert((stride[u] > block[u]) || ((stride[u] == block[u])
-                            && (count[u] == H5S_UNLIMITED)));
-                    int_stride[u]=stride[u];
-                } /* end else */
-                int_count[u]=count[u];
-                int_block[u]=block[u];
-            } /* end else */
-        } /* end for */
-    } /* end else */
-
-    /* Check for operating on unlimited selection */
-    if((H5S_GET_SELECT_TYPE(space) == H5S_SEL_HYPERSLABS)
-            && (space->select.sel_info.hslab->unlim_dim >= 0)
-            && (op != H5S_SELECT_SET))
-            {
-        /* Check for invalid operation */
-        if(unlim_dim >= 0)
-            HGOTO_ERROR(H5E_DATASPACE, H5E_UNSUPPORTED, FAIL, "cannot modify unlimited selection with another unlimited selection")
-        if(!((op == H5S_SELECT_AND) || (op == H5S_SELECT_NOTA)))
-            HGOTO_ERROR(H5E_DATASPACE, H5E_UNSUPPORTED, FAIL, "unsupported operation on unlimited selection")
-        HDassert(space->select.sel_info.hslab->diminfo_valid);
+    if(H5S_GET_SELECT_TYPE(old_space) == H5S_SEL_HYPERSLABS) {
+        hsize_t *old_low_bounds;                /* Pointer to old space's low & high bounds */
+        hsize_t *old_high_bounds;
+        hsize_t new_low_bounds[H5S_MAX_RANK];   /* New space's low & high bounds */
+        hsize_t new_high_bounds[H5S_MAX_RANK];
+        hbool_t overlapped = FALSE;
+
+        /* Set up old space's low & high bounds */
+        if(old_space->select.sel_info.hslab->span_lst) {
+            old_low_bounds = old_space->select.sel_info.hslab->span_lst->low_bounds;
+            old_high_bounds = old_space->select.sel_info.hslab->span_lst->high_bounds;
+        } /* end if */
+        else {
+            old_low_bounds = old_space->select.sel_info.hslab->diminfo.low_bounds;
+            old_high_bounds = old_space->select.sel_info.hslab->diminfo.high_bounds;
+        } /* end else */
 
-        /* Clip unlimited selection to include new selection */
-        if(H5S_hyper_clip_unlim(space,
-                start[space->select.sel_info.hslab->unlim_dim]
-                + ((opt_count[space->select.sel_info.hslab->unlim_dim]
-                - (hsize_t)1)
-                * opt_stride[space->select.sel_info.hslab->unlim_dim])
-                + opt_block[space->select.sel_info.hslab->unlim_dim]) < 0)
-            HGOTO_ERROR(H5E_DATASPACE, H5E_CANTCLIP, FAIL, "failed to clip unlimited selection")
+        /* Generate bounding box for hyperslab parameters */
+        for(u = 0; u < old_space->extent.rank; u++) {
+            new_low_bounds[u] = start[u];
+            new_high_bounds[u] = start[u] + stride[u] * (count[u] - 1) + (block[u] - 1);
+        } /* end for */
 
-        /* If an empty space was returned it must be "none" */
-        HDassert((space->select.num_elem > (hsize_t)0)
-                || (space->select.type->type == H5S_SEL_NONE));
-    } /* end if */
+        /* Check bound box of both spaces to see if they overlap */
+        if(H5S_RANGE_OVERLAP(old_low_bounds[0], old_high_bounds[0],
+                new_low_bounds[0], new_high_bounds[0]))
+            overlapped = TRUE;
+
+        /* Non-overlapping situations can be handled in special ways */
+        if(!overlapped) {
+            H5S_hyper_span_info_t *new_spans = NULL;
+            H5S_hyper_dim_t new_hyper_diminfo[H5S_MAX_RANK];
+
+            if(NULL == ((*new_space) = H5S_copy(old_space, TRUE, TRUE)))
+                HGOTO_ERROR(H5E_DATASPACE, H5E_CANTCOPY, FAIL, "unable to copy dataspace")
+            if(NULL != (*new_space)->select.sel_info.hslab->span_lst) {
+                old_space->select.sel_info.hslab->span_lst->count--;
+                (*new_space)->select.sel_info.hslab->span_lst = NULL;
+            } /* end if */
 
-    /* Fixup operation for non-hyperslab selections */
-    switch(H5S_GET_SELECT_TYPE(space)) {
-        case H5S_SEL_NONE:   /* No elements selected in dataspace */
+            /* Generate hyperslab info for new space */
             switch(op) {
-                case H5S_SELECT_SET:   /* Select "set" operation */
-                    /* Change "none" selection to hyperslab selection */
-                    break;
+                case H5S_SELECT_OR:
+                case H5S_SELECT_XOR:
+                    /* Add the new space to the space */
+                    if(NULL == (new_spans = H5S__hyper_make_spans(old_space->extent.rank, start, stride, count, block)))
+                        HGOTO_ERROR(H5E_DATASPACE, H5E_CANTINSERT, FAIL, "can't create hyperslab information")
+                    if(NULL != old_space->select.sel_info.hslab->span_lst)
+                        (*new_space)->select.sel_info.hslab->span_lst = H5S__hyper_copy_span(old_space->select.sel_info.hslab->span_lst, old_space->extent.rank);
+                    if(H5S__hyper_add_disjoint_spans(*new_space, new_spans) < 0)
+                        HGOTO_ERROR(H5E_DATASPACE, H5E_CANTINSERT, FAIL, "can't append hyperslabs")
+
+                    /* Build diminfo struct */
+                    for(u = 0; u < (*new_space)->extent.rank; u++) {
+                        new_hyper_diminfo[u].start = start[u];
+                        new_hyper_diminfo[u].stride = stride[u];
+                        new_hyper_diminfo[u].count = count[u];
+                        new_hyper_diminfo[u].block = block[u];
+                    } /* end for */
 
-                case H5S_SELECT_OR:    /* Binary "or" operation for hyperslabs */
-                case H5S_SELECT_XOR:   /* Binary "xor" operation for hyperslabs */
-                case H5S_SELECT_NOTA:  /* Binary "B not A" operation for hyperslabs */
-                    op=H5S_SELECT_SET; /* Maps to "set" operation when applied to "none" selection */
+                    /* Update space's dim info */
+                    if(H5S__hyper_update_diminfo(*new_space, op, new_hyper_diminfo) < 0)
+                        HGOTO_ERROR(H5E_DATASPACE, H5E_CANTCOUNT, FAIL, "can't update hyperslab info")
                     break;
 
-                case H5S_SELECT_AND:   /* Binary "and" operation for hyperslabs */
-                case H5S_SELECT_NOTB:  /* Binary "A not B" operation for hyperslabs */
-                    HGOTO_DONE(SUCCEED);        /* Selection stays "none" */
-
-                default:
-                    HGOTO_ERROR(H5E_ARGS, H5E_UNSUPPORTED, FAIL, "invalid selection operation")
-            } /* end switch */
-            break;
-
-        case H5S_SEL_ALL:    /* All elements selected in dataspace */
-            switch(op) {
-                case H5S_SELECT_SET:   /* Select "set" operation */
-                    /* Change "all" selection to hyperslab selection */
+                case H5S_SELECT_AND:
+                    if(H5S_select_none((*new_space)) < 0)
+                        HGOTO_ERROR(H5E_DATASPACE, H5E_CANTSELECT, FAIL, "can't convert selection")
                     break;
 
-                case H5S_SELECT_OR:    /* Binary "or" operation for hyperslabs */
-                    HGOTO_DONE(SUCCEED);        /* Selection stays "all" */
-
-                case H5S_SELECT_AND:   /* Binary "and" operation for hyperslabs */
-                    op=H5S_SELECT_SET; /* Maps to "set" operation when applied to "none" selection */
+                case H5S_SELECT_NOTB:
+                    if(NULL != old_space->select.sel_info.hslab->span_lst) {
+                        if(NULL == ((*new_space)->select.sel_info.hslab->span_lst = H5S__hyper_copy_span(old_space->select.sel_info.hslab->span_lst, old_space->extent.rank)))
+                            HGOTO_ERROR(H5E_DATASPACE, H5E_CANTCOPY, FAIL, "unable to copy dataspace")
+                    } /* end if */
+                    else {
+                        if(H5S_select_none((*new_space)) < 0)
+                            HGOTO_ERROR(H5E_DATASPACE, H5E_CANTSELECT, FAIL, "can't convert selection")
+                    } /* end else */
                     break;
 
-                case H5S_SELECT_XOR:   /* Binary "xor" operation for hyperslabs */
-                case H5S_SELECT_NOTB:  /* Binary "A not B" operation for hyperslabs */
-                    /* Convert current "all" selection to "real" hyperslab selection */
-                    /* Then allow operation to proceed */
-                    {
-                        hsize_t tmp_start[H5S_MAX_RANK];   /* Temporary start information */
-                        hsize_t tmp_stride[H5S_MAX_RANK];   /* Temporary stride information */
-                        hsize_t tmp_count[H5S_MAX_RANK];    /* Temporary count information */
-                        hsize_t tmp_block[H5S_MAX_RANK];    /* Temporary block information */
-
-                        /* Fill in temporary information for the dimensions */
-                        for(u=0; u<space->extent.rank; u++) {
-                            tmp_start[u]=0;
-                            tmp_stride[u]=1;
-                            tmp_count[u]=1;
-                            tmp_block[u]=space->extent.size[u];
-                        } /* end for */
-
-                        /* Convert to hyperslab selection */
-                        if(H5S_select_hyperslab(space,H5S_SELECT_SET,tmp_start,tmp_stride,tmp_count,tmp_block)<0)
-                            HGOTO_ERROR(H5E_DATASPACE, H5E_CANTDELETE, FAIL, "can't convert selection")
-                    } /* end case */
+                case H5S_SELECT_NOTA:
+                    if(H5S__set_regular_hyperslab(*new_space, start, stride, count, block, stride, count, block) < 0)
+                        HGOTO_ERROR(H5E_DATASPACE, H5E_CANTSET, FAIL, "can't set regular selection")
                     break;
 
-                case H5S_SELECT_NOTA:  /* Binary "B not A" operation for hyperslabs */
-                    /* Convert to "none" selection */
-                    if(H5S_select_none(space)<0)
-                        HGOTO_ERROR(H5E_DATASPACE, H5E_CANTDELETE, FAIL, "can't convert selection")
-                    HGOTO_DONE(SUCCEED);
-
+                case H5S_SELECT_NOOP:
+                case H5S_SELECT_SET:
+                case H5S_SELECT_APPEND:
+                case H5S_SELECT_PREPEND:
+                case H5S_SELECT_INVALID:
                 default:
                     HGOTO_ERROR(H5E_ARGS, H5E_UNSUPPORTED, FAIL, "invalid selection operation")
             } /* end switch */
-            break;
-
-        case H5S_SEL_HYPERSLABS:
-            /* Hyperslab operation on hyperslab selection, OK */
-            break;
-
-        case H5S_SEL_POINTS: /* Can't combine hyperslab operations and point selections currently */
-            if(op==H5S_SELECT_SET)      /* Allow only "set" operation to proceed */
-                break;
-            /* Else fall through to error */
-
-        default:
-            HGOTO_ERROR(H5E_ARGS, H5E_UNSUPPORTED, FAIL, "invalid selection operation")
-    } /* end switch */
-
-
-    if(op==H5S_SELECT_SET) {
-        /* If we are setting a new selection, remove current selection first */
-        if(H5S_SELECT_RELEASE(space)<0)
-            HGOTO_ERROR(H5E_DATASPACE, H5E_CANTDELETE, FAIL, "can't release hyperslab")
-
-        /* Allocate space for the hyperslab selection information */
-        if(NULL == (space->select.sel_info.hslab = H5FL_MALLOC(H5S_hyper_sel_t)))
-            HGOTO_ERROR(H5E_RESOURCE, H5E_NOSPACE, FAIL, "can't allocate hyperslab info")
-
-        /* Save the diminfo */
-        space->select.num_elem=1;
-        for(u=0; u<space->extent.rank; u++) {
-            space->select.sel_info.hslab->diminfo.app[u].start = start[u];
-            space->select.sel_info.hslab->diminfo.app[u].stride = stride[u];
-            space->select.sel_info.hslab->diminfo.app[u].count = count[u];
-            space->select.sel_info.hslab->diminfo.app[u].block = block[u];
-
-            space->select.sel_info.hslab->diminfo.opt[u].start = start[u];
-            space->select.sel_info.hslab->diminfo.opt[u].stride = opt_stride[u];
-            space->select.sel_info.hslab->diminfo.opt[u].count = opt_count[u];
-            space->select.sel_info.hslab->diminfo.opt[u].block = opt_block[u];
-
-            space->select.num_elem*=(opt_count[u]*opt_block[u]);
-        } /* end for */
-
-        /* Save unlim_dim */
-        space->select.sel_info.hslab->unlim_dim = unlim_dim;
-
-        /* Indicate that the dimension information is valid */
-        space->select.sel_info.hslab->diminfo_valid = H5S_DIMINFO_VALID_YES;
 
-        /* Indicate that there's no slab information */
-        space->select.sel_info.hslab->span_lst = NULL;
+            HGOTO_DONE(SUCCEED);
+        } /* end if(!overlapped) */
+    } /* end if the selection of old space is H5S_SEL_HYPERSLABS */
 
-        /* Handle unlimited selections */
-        if(unlim_dim >= 0) {
-            /* Calculate num_elem_non_unlim */
-            space->select.sel_info.hslab->num_elem_non_unlim = (hsize_t)1;
-            for(u = 0; u < space->extent.rank; u++)
-                if((int)u != unlim_dim)
-                    space->select.sel_info.hslab->num_elem_non_unlim *= (opt_count[u] * opt_block[u]);
+    /* Copy the first dataspace with sharing the list of spans */
+    if(NULL == ((*new_space) = H5S_copy(old_space, TRUE, TRUE)))
+        HGOTO_ERROR(H5E_DATASPACE, H5E_CANTINIT, FAIL, "unable to copy dataspace")
 
-            /* Set num_elem */
-            if(space->select.num_elem != (hsize_t)0)
-                space->select.num_elem = H5S_UNLIMITED;
-        } /* end if */
-    } /* end if */
-    else if(op>=H5S_SELECT_OR && op<=H5S_SELECT_NOTA) {
-        /* Sanity check */
-        HDassert(H5S_GET_SELECT_TYPE(space) == H5S_SEL_HYPERSLABS);
-
-        /* Handle unlimited selections */
-        if(unlim_dim >= 0) {
-            hsize_t bounds_start[H5S_MAX_RANK];
-            hsize_t bounds_end[H5S_MAX_RANK];
-            hsize_t tmp_count = opt_count[unlim_dim];
-            hsize_t tmp_block = opt_block[unlim_dim];
-
-            /* Check for invalid operation */
-            if(space->select.sel_info.hslab->unlim_dim >= 0)
-                HGOTO_ERROR(H5E_DATASPACE, H5E_UNSUPPORTED, FAIL, "cannot modify unlimited selection with another unlimited selection")
-            if(!((op == H5S_SELECT_AND) || (op == H5S_SELECT_NOTB)))
-                HGOTO_ERROR(H5E_DATASPACE, H5E_UNSUPPORTED, FAIL, "unsupported operation with unlimited selection")
-
-            /* Get bounds of existing selection */
-            if(H5S__hyper_bounds(space, bounds_start, bounds_end) < 0)
-                HGOTO_ERROR(H5E_DATASPACE, H5E_CANTGET, FAIL, "can't get selection bounds")
-
-            /* Patch count and block to remove unlimited and include the
-             * existing selection */
-            H5S__hyper_get_clip_diminfo(start[unlim_dim], opt_stride[unlim_dim], &tmp_count, &tmp_block, bounds_end[unlim_dim] + (hsize_t)1);
-            HDassert((tmp_count == 1) || (opt_count != H5S_hyper_ones_g));
-            HDassert((tmp_block == 1) || (opt_block != H5S_hyper_ones_g));
-            if(opt_count != H5S_hyper_ones_g) {
-                HDassert(opt_count == int_count);
-                int_count[unlim_dim] = tmp_count;
-            } /* end if */
-            if(opt_block != H5S_hyper_ones_g) {
-                HDassert(opt_block == int_block);
-                int_block[unlim_dim] = tmp_block;
-            } /* end if */
-        } /* end if */
-
-        /* Check if there's no hyperslab span information currently */
-        if(NULL == space->select.sel_info.hslab->span_lst)
-            if(H5S__hyper_generate_spans(space) < 0)
-                HGOTO_ERROR(H5E_DATASPACE, H5E_UNINITIALIZED, FAIL, "dataspace does not have span tree")
-
-        /* Indicate that the regular dimensions are no longer valid */
-        space->select.sel_info.hslab->diminfo_valid = H5S_DIMINFO_VALID_NO;
-
-        /* Add in the new hyperslab information */
-        if(H5S__generate_hyperslab (space, op, start, opt_stride, opt_count, opt_block)<0)
-            HGOTO_ERROR(H5E_DATASPACE, H5E_CANTINSERT, FAIL, "can't generate hyperslabs")
-    } /* end if */
-    else
-        HGOTO_ERROR(H5E_ARGS, H5E_UNSUPPORTED, FAIL, "invalid selection operation")
-
-    /* Set selection type */
-    space->select.type = H5S_sel_hyper;
+    /* Note: a little overhead in calling the function as some conditions are checked again */
+    if(H5S_select_hyperslab(*new_space, op, start, stride, count, block) < 0)
+        HGOTO_ERROR(H5E_DATASPACE, H5E_CANTINIT, FAIL, "unable to set hyperslab selection")
 
 done:
     FUNC_LEAVE_NOAPI(ret_value)
-}   /* end H5S_select_hyperslab() */
+} /* end H5S_combine_hyperslab() */
 
 
-/*--------------------------------------------------------------------------
- NAME
-    H5Sselect_hyperslab
- PURPOSE
-    Specify a hyperslab to combine with the current hyperslab selection
- USAGE
-    herr_t H5Sselect_hyperslab(dsid, op, start, stride, count, block)
-        hid_t dsid;             IN: Dataspace ID of selection to modify
-        H5S_seloper_t op;       IN: Operation to perform on current selection
-        const hsize_t *start;        IN: Offset of start of hyperslab
-        const hsize_t *stride;       IN: Hyperslab stride
-        const hsize_t *count;        IN: Number of blocks included in hyperslab
-        const hsize_t *block;        IN: Size of block in hyperslab
- RETURNS
-    Non-negative on success/Negative on failure
- DESCRIPTION
-    Combines a hyperslab selection with the current selection for a dataspace.
-    If the current selection is not a hyperslab, it is freed and the hyperslab
-    parameters passed in are combined with the H5S_SEL_ALL hyperslab (ie. a
-    selection composing the entire current extent).  If STRIDE or BLOCK is
-    NULL, they are assumed to be set to all '1'.
- GLOBAL VARIABLES
- COMMENTS, BUGS, ASSUMPTIONS
- EXAMPLES
- REVISION LOG
---------------------------------------------------------------------------*/
-herr_t
-H5Sselect_hyperslab(hid_t space_id, H5S_seloper_t op, const hsize_t start[],
-         const hsize_t stride[], const hsize_t count[], const hsize_t block[])
+/*-------------------------------------------------------------------------
+ * Function:    H5S__fill_in_select
+ *
+ * Purpose:    Combines two hyperslabs with an operation, putting the
+ *              result into a third hyperslab selection
+ *
+ * Return:    Non-negative on success/negative on failure
+ *
+ * Programmer:    Chao Mei
+ *              Tuesday, July 5, 2011
+ *
+ *-------------------------------------------------------------------------
+ */
+static herr_t
+H5S__fill_in_select(H5S_t *space1, H5S_seloper_t op, H5S_t *space2, H5S_t **result)
 {
-    H5S_t	*space = NULL;  /* Dataspace to modify selection of */
-    herr_t      ret_value=SUCCEED;       /* Return value */
-
-    FUNC_ENTER_API(FAIL)
-    H5TRACE6("e", "iSs*h*h*h*h", space_id, op, start, stride, count, block);
+    hbool_t span2_owned;
+    hbool_t updated_spans;
+    herr_t ret_value = SUCCEED;         /* Return value */
 
-    /* Check args */
-    if (NULL == (space = (H5S_t *)H5I_object_verify(space_id, H5I_DATASPACE)))
-        HGOTO_ERROR(H5E_ARGS, H5E_BADTYPE, FAIL, "not a dataspace")
-    if (H5S_SCALAR==H5S_GET_EXTENT_TYPE(space))
-        HGOTO_ERROR(H5E_ARGS, H5E_BADTYPE, FAIL, "hyperslab doesn't support H5S_SCALAR space")
-    if (H5S_NULL==H5S_GET_EXTENT_TYPE(space))
-        HGOTO_ERROR(H5E_ARGS, H5E_BADTYPE, FAIL, "hyperslab doesn't support H5S_NULL space")
-    if(start==NULL || count==NULL)
-        HGOTO_ERROR(H5E_ARGS, H5E_BADVALUE, FAIL, "hyperslab not specified")
-    if(!(op>H5S_SELECT_NOOP && op<H5S_SELECT_INVALID))
-        HGOTO_ERROR(H5E_ARGS, H5E_UNSUPPORTED, FAIL, "invalid selection operation")
-    if(stride!=NULL) {
-        unsigned u;             /* Local index variable */
+    FUNC_ENTER_STATIC
 
-        /* Check for 0-sized strides */
-        for(u=0; u<space->extent.rank; u++) {
-            if(stride[u]==0)
-                HGOTO_ERROR(H5E_ARGS, H5E_BADVALUE, FAIL, "invalid stride==0 value")
-        } /* end for */
+    /* Sanity check */
+    HDassert(space1);
+    HDassert(space2);
+    HDassert(op >= H5S_SELECT_OR && op <= H5S_SELECT_NOTA);
+    HDassert(space1->extent.rank == space2->extent.rank);
+    /* The result is either a to-be-created space or an empty one */
+    HDassert(NULL == *result || *result == space1);
+    HDassert(space1->select.sel_info.hslab->span_lst);
+    HDassert(space2->select.sel_info.hslab->span_lst);
+
+    /* Note: the offset of space2 is not considered here for bounding box */
+    if(H5S__fill_in_new_space(space1, op, space2->select.sel_info.hslab->span_lst, FALSE, &span2_owned, &updated_spans, result) < 0)
+        HGOTO_ERROR(H5E_DATASPACE, H5E_CANTSELECT, FAIL, "can't create the specified selection")
+
+    /* Update diminfo if space2's diminfo was valid, otherwise just mark it as
+     * invalid if the spans were updated */
+    HDassert(result);
+    if(updated_spans) {
+        if(space2->select.sel_info.hslab->diminfo_valid == H5S_DIMINFO_VALID_YES) {
+            if(H5S__hyper_update_diminfo(*result, op, space2->select.sel_info.hslab->diminfo.opt) < 0)
+                HGOTO_ERROR(H5E_DATASPACE, H5E_CANTCOUNT, FAIL, "can't update hyperslab info")
+        } /* end if */
+        else
+            (*result)->select.sel_info.hslab->diminfo_valid = H5S_DIMINFO_VALID_NO;
     } /* end if */
 
-    if (H5S_select_hyperslab(space, op, start, stride, count, block)<0)
-        HGOTO_ERROR(H5E_DATASPACE, H5E_CANTINIT, FAIL, "unable to set hyperslab selection")
-
 done:
-    FUNC_LEAVE_API(ret_value)
-} /* end H5Sselect_hyperslab() */
+    FUNC_LEAVE_NOAPI(ret_value)
+} /* end H5S__fill_in_select() */
 
 
 /*--------------------------------------------------------------------------
@@ -7664,7 +10287,7 @@ done:
     return a new dataspace with the combined selection as the selection in the
     new dataspace.
  USAGE
-    hid_t H5Srefine_hyperslab(dsid, op, start, stride, count, block)
+    hid_t H5Scombine_hyperslab(dsid, op, start, stride, count, block)
         hid_t dsid;             IN: Dataspace ID of selection to use
         H5S_seloper_t op;       IN: Operation to perform on current selection
         const hsize_t *start;        IN: Offset of start of hyperslab
@@ -7704,12 +10327,8 @@ H5Scombine_hyperslab(hid_t space_id, H5S_seloper_t op, const hsize_t start[],
     if(!(op >= H5S_SELECT_SET && op <= H5S_SELECT_NOTA))
         HGOTO_ERROR(H5E_ARGS, H5E_UNSUPPORTED, H5I_INVALID_HID, "invalid selection operation")
 
-    /* Copy the first dataspace */
-    if (NULL == (new_space = H5S_copy (space, TRUE, TRUE)))
-        HGOTO_ERROR(H5E_DATASPACE, H5E_CANTINIT, H5I_INVALID_HID, "unable to copy dataspace")
-
-    /* Go modify the selection in the new dataspace */
-    if (H5S_select_hyperslab(new_space, op, start, stride, count, block)<0)
+    /* Generate new space, with combination of selections */
+    if(H5S_combine_hyperslab(space, op, start, stride, count, block, &new_space) < 0)
         HGOTO_ERROR(H5E_DATASPACE, H5E_CANTINIT, H5I_INVALID_HID, "unable to set hyperslab selection")
 
     /* Atomize */
@@ -7740,7 +10359,6 @@ static H5S_t *
 H5S__combine_select(H5S_t *space1, H5S_seloper_t op, H5S_t *space2)
 {
     H5S_t *new_space = NULL;    /* New dataspace generated */
-    hbool_t span2_owned=FALSE;          /* Flag to indicate that span2 was used in H5S_operate_hyperslab() */
     H5S_t *ret_value = NULL;    /* Return value */
 
     FUNC_ENTER_STATIC
@@ -7750,34 +10368,38 @@ H5S__combine_select(H5S_t *space1, H5S_seloper_t op, H5S_t *space2)
     HDassert(space2);
     HDassert(op >= H5S_SELECT_OR && op <= H5S_SELECT_NOTA);
 
-    /* Check that the space selections both have span trees */
-    if(space1->select.sel_info.hslab->span_lst==NULL)
-        if(H5S__hyper_generate_spans(space1)<0)
-            HGOTO_ERROR(H5E_DATASPACE, H5E_UNINITIALIZED, NULL, "dataspace does not have span tree")
-    if(space2->select.sel_info.hslab->span_lst==NULL)
-        if(H5S__hyper_generate_spans(space2)<0)
+    /* Check if space1 selections has span trees */
+    if(NULL == space1->select.sel_info.hslab->span_lst)
+        if(H5S__hyper_generate_spans(space1) < 0)
             HGOTO_ERROR(H5E_DATASPACE, H5E_UNINITIALIZED, NULL, "dataspace does not have span tree")
 
-    /* Copy the first dataspace */
-    if (NULL == (new_space = H5S_copy (space1, TRUE, TRUE)))
-        HGOTO_ERROR(H5E_DATASPACE, H5E_CANTINIT, NULL, "unable to copy dataspace")
-
-    /* Free the current selection for the new dataspace */
-    if(H5S_SELECT_RELEASE(new_space)<0)
-        HGOTO_ERROR(H5E_DATASPACE, H5E_CANTDELETE, NULL, "can't release selection")
+    if(NULL == space2->select.sel_info.hslab->span_lst) {
+        hsize_t tmp_start[H5S_MAX_RANK];
+        hsize_t tmp_stride[H5S_MAX_RANK];
+        hsize_t tmp_count[H5S_MAX_RANK];
+        hsize_t tmp_block[H5S_MAX_RANK];
+        unsigned u;
+
+        for(u = 0; u < space2->extent.rank; u++) {
+            tmp_start[u] = space2->select.sel_info.hslab->diminfo.opt[u].start;
+            tmp_stride[u] = space2->select.sel_info.hslab->diminfo.opt[u].stride;
+            tmp_count[u] = space2->select.sel_info.hslab->diminfo.opt[u].count;
+            tmp_block[u] = space2->select.sel_info.hslab->diminfo.opt[u].block;
+        } /* end for */
 
-    /* Allocate space for the hyperslab selection information */
-    if((new_space->select.sel_info.hslab = H5FL_CALLOC(H5S_hyper_sel_t)) == NULL)
-        HGOTO_ERROR(H5E_RESOURCE, H5E_NOSPACE, NULL, "can't allocate hyperslab info")
-    new_space->select.sel_info.hslab->diminfo_valid = H5S_DIMINFO_VALID_NO;
+        /* Combine hyperslab selection with regular selection directly */
+        if(H5S_combine_hyperslab(space1, op, tmp_start, tmp_stride, tmp_count, tmp_block, &new_space) < 0)
+            HGOTO_ERROR(H5E_DATASPACE, H5E_CANTINIT, NULL, "unable to set hyperslab selection")
+    } /* end if */
+    else{
+        /* Combine new_space (a copy of space 1) & space2, with the result in new_space */
+        if(H5S__fill_in_select(space1, op, space2, &new_space) < 0)
+            HGOTO_ERROR(H5E_DATASPACE, H5E_CANTCLIP, NULL, "can't clip hyperslab information")
+    } /* end else */
 
     /* Set unlim_dim */
     new_space->select.sel_info.hslab->unlim_dim = -1;
 
-    /* Combine space1 & space2, with the result in new_space */
-    if(H5S_operate_hyperslab(new_space,space1->select.sel_info.hslab->span_lst,op,space2->select.sel_info.hslab->span_lst,FALSE,&span2_owned)<0)
-        HGOTO_ERROR(H5E_DATASPACE, H5E_CANTCLIP, NULL, "can't clip hyperslab information")
-
     /* Set return value */
     ret_value = new_space;
 
@@ -7814,37 +10436,47 @@ done:
 hid_t
 H5Scombine_select(hid_t space1_id, H5S_seloper_t op, hid_t space2_id)
 {
-    H5S_t	*space1;                /* First Dataspace */
-    H5S_t	*space2;                /* Second Dataspace */
-    H5S_t	*new_space = NULL;      /* New Dataspace */
-    hid_t	ret_value;              /* Return value */
+    H5S_t    *space1;                /* First Dataspace */
+    H5S_t    *space2;                /* Second Dataspace */
+    H5S_t    *new_space = NULL;      /* New Dataspace */
+    hid_t    ret_value;              /* Return value */
 
-    FUNC_ENTER_API(FAIL)
+    FUNC_ENTER_API(H5I_INVALID_HID)
     H5TRACE3("i", "iSsi", space1_id, op, space2_id);
 
     /* Check args */
     if(NULL == (space1 = (H5S_t *)H5I_object_verify(space1_id, H5I_DATASPACE)))
-        HGOTO_ERROR(H5E_ARGS, H5E_BADTYPE, FAIL, "not a dataspace")
+        HGOTO_ERROR(H5E_ARGS, H5E_BADTYPE, H5I_INVALID_HID, "not a dataspace")
     if(NULL == (space2 = (H5S_t *)H5I_object_verify(space2_id, H5I_DATASPACE)))
-        HGOTO_ERROR(H5E_ARGS, H5E_BADTYPE, FAIL, "not a dataspace")
+        HGOTO_ERROR(H5E_ARGS, H5E_BADTYPE, H5I_INVALID_HID, "not a dataspace")
     if(!(op >= H5S_SELECT_OR && op <= H5S_SELECT_NOTA))
-        HGOTO_ERROR(H5E_ARGS, H5E_UNSUPPORTED, FAIL, "invalid selection operation")
+        HGOTO_ERROR(H5E_ARGS, H5E_UNSUPPORTED, H5I_INVALID_HID, "invalid selection operation")
 
     /* Check that both dataspaces have the same rank */
     if(space1->extent.rank != space2->extent.rank)
-        HGOTO_ERROR(H5E_ARGS, H5E_BADVALUE, FAIL, "dataspaces not same rank")
+        HGOTO_ERROR(H5E_ARGS, H5E_BADVALUE, H5I_INVALID_HID, "dataspaces not same rank")
+
+    /* Note: currently, the offset of each dataspace is ignored */
+#if 0
+    /* Check that both dataspaces have the same offset */
+    /* Same note as in H5Smodify_select */
+    for(u=0; u<space1->extent.rank; u++) {
+        if(space1->select.offset[u] != space2->select.offset[u])
+            HGOTO_ERROR(H5E_ARGS, H5E_BADVALUE, H5I_INVALID_HID, "dataspaces not same offset")
+    } /* end for */
+#endif
 
     /* Check that both dataspaces have hyperslab selections */
     if(H5S_GET_SELECT_TYPE(space1) != H5S_SEL_HYPERSLABS || H5S_GET_SELECT_TYPE(space2) != H5S_SEL_HYPERSLABS)
-        HGOTO_ERROR(H5E_ARGS, H5E_BADVALUE, FAIL, "dataspaces don't have hyperslab selections")
+        HGOTO_ERROR(H5E_ARGS, H5E_BADVALUE, H5I_INVALID_HID, "dataspaces don't have hyperslab selections")
 
     /* Go combine the dataspaces */
     if(NULL == (new_space = H5S__combine_select(space1, op, space2)))
-        HGOTO_ERROR(H5E_DATASPACE, H5E_CANTINIT, FAIL, "unable to create hyperslab selection")
+        HGOTO_ERROR(H5E_DATASPACE, H5E_CANTINIT, H5I_INVALID_HID, "unable to create hyperslab selection")
 
     /* Atomize */
     if((ret_value = H5I_register(H5I_DATASPACE, new_space, TRUE)) < 0)
-        HGOTO_ERROR(H5E_ATOM, H5E_CANTREGISTER, FAIL, "unable to register dataspace atom")
+        HGOTO_ERROR(H5E_ATOM, H5E_CANTREGISTER, H5I_INVALID_HID, "unable to register dataspace atom")
 
 done:
     if(ret_value < 0 && new_space)
@@ -7857,7 +10489,7 @@ done:
 /*-------------------------------------------------------------------------
  * Function:    H5S__modify_select
  *
- * Purpose:     Internal version of H5Sselect_select().
+ * Purpose:     Internal version of H5Smodify_select().
  *
  * Return:      New dataspace on success/NULL on failure
  *
@@ -7869,8 +10501,6 @@ done:
 herr_t
 H5S__modify_select(H5S_t *space1, H5S_seloper_t op, H5S_t *space2)
 {
-    H5S_hyper_span_info_t *tmp_spans = NULL;   /* Temporary copy of selection */
-    hbool_t span2_owned=FALSE;          /* Flag to indicate that span2 was used in H5S_operate_hyperslab() */
     herr_t      ret_value = SUCCEED;       /* Return value */
 
     FUNC_ENTER_PACKAGE
@@ -7878,53 +10508,52 @@ H5S__modify_select(H5S_t *space1, H5S_seloper_t op, H5S_t *space2)
     /* Check args */
     HDassert(space1);
     HDassert(space2);
-    HDassert(op > H5S_SELECT_NOOP && op < H5S_SELECT_INVALID);
+    HDassert(op >= H5S_SELECT_OR && op <= H5S_SELECT_NOTA);
 
     /* Check that the space selections both have span trees */
-    if(space1->select.sel_info.hslab->span_lst==NULL)
-        if(H5S__hyper_generate_spans(space1)<0)
-            HGOTO_ERROR(H5E_DATASPACE, H5E_UNINITIALIZED, FAIL, "dataspace does not have span tree")
-    if(space2->select.sel_info.hslab->span_lst==NULL)
-        if(H5S__hyper_generate_spans(space2)<0)
+    if(NULL == space1->select.sel_info.hslab->span_lst)
+        if(H5S__hyper_generate_spans(space1) < 0)
             HGOTO_ERROR(H5E_DATASPACE, H5E_UNINITIALIZED, FAIL, "dataspace does not have span tree")
 
-    /* Take ownership of the dataspace's hyperslab spans */
-    /* (These are freed later) */
-    tmp_spans=space1->select.sel_info.hslab->span_lst;
-    space1->select.sel_info.hslab->span_lst=NULL;
-
-    /* Reset the other dataspace selection information */
-    if(H5S_SELECT_RELEASE(space1)<0)
-        HGOTO_ERROR(H5E_DATASPACE, H5E_CANTDELETE, FAIL, "can't release selection")
-
-    /* Allocate space for the hyperslab selection information */
-    if((space1->select.sel_info.hslab = H5FL_CALLOC(H5S_hyper_sel_t)) == NULL)
-        HGOTO_ERROR(H5E_RESOURCE, H5E_NOSPACE, FAIL, "can't allocate hyperslab info")
-    space1->select.sel_info.hslab->diminfo_valid = H5S_DIMINFO_VALID_NO;
-
     /* Set unlim_dim */
     space1->select.sel_info.hslab->unlim_dim = -1;
 
-    /* Combine tmp_spans (from space1) & spans from space2, with the result in space1 */
-    if(H5S_operate_hyperslab(space1,tmp_spans,op,space2->select.sel_info.hslab->span_lst,FALSE,&span2_owned)<0)
-        HGOTO_ERROR(H5E_DATASPACE, H5E_CANTCLIP, FAIL, "can't clip hyperslab information")
+    if(NULL == space2->select.sel_info.hslab->span_lst) {
+        hsize_t tmp_start[H5S_MAX_RANK];
+        hsize_t tmp_stride[H5S_MAX_RANK];
+        hsize_t tmp_count[H5S_MAX_RANK];
+        hsize_t tmp_block[H5S_MAX_RANK];
+        unsigned u;
+
+        for(u = 0; u < space2->extent.rank; u++) {
+            tmp_start[u] = space2->select.sel_info.hslab->diminfo.opt[u].start;
+            tmp_stride[u] = space2->select.sel_info.hslab->diminfo.opt[u].stride;
+            tmp_count[u] = space2->select.sel_info.hslab->diminfo.opt[u].count;
+            tmp_block[u] = space2->select.sel_info.hslab->diminfo.opt[u].block;
+        } /* end for */
 
-done:
-    if(tmp_spans!=NULL)
-        H5S__hyper_free_span_info(tmp_spans);
+        /* Call H5S_select_hyperslab directly */
+        if(H5S_select_hyperslab(space1, op, tmp_start, tmp_stride, tmp_count, tmp_block) < 0)
+            HGOTO_ERROR(H5E_DATASPACE, H5E_CANTINIT, FAIL, "unable to set hyperslab selection")
+    } /* end if */
+    else
+        /* Combine spans from space1 & spans from space2, with the result in space1 */
+        if(H5S__fill_in_select(space1, op, space2, &space1) < 0)
+            HGOTO_ERROR(H5E_DATASPACE, H5E_CANTCLIP, FAIL, "can't perform operation on two selections")
 
+done:
     FUNC_LEAVE_NOAPI(ret_value)
 } /* end H5S__modify_select() */
 
 
 /*--------------------------------------------------------------------------
  NAME
-    H5Sselect_select
+    H5Smodify_select
  PURPOSE
     Refine a hyperslab selection with an operation using a second hyperslab
     to modify it
  USAGE
-    herr_t H5Sselect_select(space1, op, space2)
+    herr_t H5Smodify_select(space1, op, space2)
         hid_t space1;           IN/OUT: First Dataspace ID
         H5S_seloper_t op;       IN: Selection operation
         hid_t space2;           IN: Second Dataspace ID
@@ -7940,10 +10569,10 @@ done:
  REVISION LOG
 --------------------------------------------------------------------------*/
 herr_t
-H5Sselect_select(hid_t space1_id, H5S_seloper_t op, hid_t space2_id)
+H5Smodify_select(hid_t space1_id, H5S_seloper_t op, hid_t space2_id)
 {
-    H5S_t   *space1;                /* First Dataspace */
-    H5S_t   *space2;                /* Second Dataspace */
+    H5S_t    *space1;                /* First Dataspace */
+    H5S_t    *space2;                /* Second Dataspace */
     herr_t      ret_value = SUCCEED;    /* Return value */
 
     FUNC_ENTER_API(FAIL)
@@ -7961,6 +10590,31 @@ H5Sselect_select(hid_t space1_id, H5S_seloper_t op, hid_t space2_id)
     if(space1->extent.rank != space2->extent.rank)
         HGOTO_ERROR(H5E_ARGS, H5E_BADVALUE, FAIL, "dataspaces not same rank")
 
+    /* Check that both dataspaces have the same offset */
+    /** Note that this is a tricky part of this function. It's
+     *  possible that two dataspaces have different "offset". If the
+     *  space2 has smaller offset value than that of space1 in a
+     *  dimension, then the span elements of this dimension in
+     *  space2 could have negative "low" and "high" values relative
+     *  to the offset in space1. In other words, if the bounds of
+     *  span elements in space2 are adjusted relative to the offset
+     *  in space1, then every span element's bound is computed as
+     *  "origin_bound+offset2-offset1". Therefore, if offset2 (the
+     *  offset of space2) is smaller, then
+     *  "origin_bound+offset2-offset1" could be negative which is
+     *  not allowed by the bound type declaration as hsize_t!
+     *  As a result, if the op is an OR selection, then the final
+     *  result may contain span elements that have negative bound!
+     *  So right now, the difference in the offset is totally
+     *  ignored!!
+     */
+#if 0
+    for(u=0; u<space1->extent.rank; u++) {
+        if(space1->select.offset[u] != space2->select.offset[u])
+            HGOTO_ERROR(H5E_ARGS, H5E_BADVALUE, FAIL, "dataspaces not same offset")
+    } /* end for */
+#endif
+
     /* Check that both dataspaces have hyperslab selections */
     if(H5S_GET_SELECT_TYPE(space1) != H5S_SEL_HYPERSLABS || H5S_GET_SELECT_TYPE(space2) != H5S_SEL_HYPERSLABS)
         HGOTO_ERROR(H5E_ARGS, H5E_BADVALUE, FAIL, "dataspaces don't have hyperslab selections")
@@ -7971,1345 +10625,652 @@ H5Sselect_select(hid_t space1_id, H5S_seloper_t op, hid_t space2_id)
 
 done:
     FUNC_LEAVE_API(ret_value)
-} /* end H5Sselect_select() */
-#endif /* NEW_HYPERSLAB_API */ /* Works */
+} /* end H5Smodify_select() */
 
 
 /*--------------------------------------------------------------------------
  NAME
-    H5S__hyper_get_seq_list_gen
+    H5S__hyper_proj_int_build_proj
  PURPOSE
-    Create a list of offsets & lengths for a selection
+    Secondary iteration routine for H5S__hyper_project_intersection
  USAGE
-    herr_t H5S_select_hyper_get_file_list_gen(space,iter,maxseq,maxelem,nseq,nelem,off,len)
-        H5S_t *space;           IN: Dataspace containing selection to use.
-        H5S_sel_iter_t *iter;   IN/OUT: Selection iterator describing last
-                                    position of interest in selection.
-        size_t maxseq;          IN: Maximum number of sequences to generate
-        size_t maxelem;         IN: Maximum number of elements to include in the
-                                    generated sequences
-        size_t *nseq;           OUT: Actual number of sequences generated
-        size_t *nelem;          OUT: Actual number of elements in sequences generated
-        hsize_t *off;           OUT: Array of offsets
-        size_t *len;            OUT: Array of lengths
+    herr_t H5S__hyper_proj_int_build_proj(udata)
+        H5S_hyper_project_intersect_ud_t *udata; IN/OUT: Persistent shared data for iteration
  RETURNS
     Non-negative on success/Negative on failure.
  DESCRIPTION
-    Use the selection in the dataspace to generate a list of byte offsets and
-    lengths for the region(s) selected.  Start/Restart from the position in the
-    ITER parameter.  The number of sequences generated is limited by the MAXSEQ
-    parameter and the number of sequences actually generated is stored in the
-    NSEQ parameter.
+    Takes the skip and nelem amounts listed in udata and converts them to
+    span trees in the projected space, using the destination space.  This
+    is a non-recursive algorithm by necessity, it saves the current state
+    of iteration in udata and resumes in the same location on subsequent
+    calls.
  GLOBAL VARIABLES
  COMMENTS, BUGS, ASSUMPTIONS
  EXAMPLES
  REVISION LOG
 --------------------------------------------------------------------------*/
 static herr_t
-H5S__hyper_get_seq_list_gen(const H5S_t *space, H5S_sel_iter_t *iter,
-    size_t maxseq, size_t maxelem, size_t *nseq, size_t *nelem,
-    hsize_t *off, size_t *len)
-{
-    H5S_hyper_span_t *curr_span;    /* Current hyperslab span node */
-    H5S_hyper_span_t **ispan;       /* Iterator's hyperslab span nodes */
-    hsize_t slab[H5S_MAX_RANK]; /* Cumulative size of each dimension in bytes */
-    hsize_t acc;       /* Accumulator for computing cumulative sizes */
-    hsize_t loc_off;   /* Element offset in the dataspace */
-    hsize_t last_span_end = 0; /* The offset of the end of the last span */
-    hsize_t *abs_arr;  /* Absolute hyperslab span position */
-    const hssize_t *off_arr;  /* Offset within the dataspace extent */
-    size_t span_size = 0; /* Number of bytes in current span to actually process */
-    size_t io_left;    /* Number of elements left to process */
-    size_t io_bytes_left;   /* Number of bytes left to process */
-    size_t io_used;    /* Number of elements processed */
-    size_t curr_seq = 0; /* Number of sequence/offsets stored in the arrays */
-    size_t elem_size;  /* Size of each element iterating over */
-    unsigned ndims;    /* Number of dimensions of dataset */
-    unsigned fast_dim; /* Rank of the fastest changing dimension for the dataspace */
-    int curr_dim;      /* Current dimension being operated on */
-    unsigned u;        /* Index variable */
-    int i;             /* Index variable */
-
-    FUNC_ENTER_STATIC_NOERR
-
-    /* Check args */
-    HDassert(space);
-    HDassert(iter);
-    HDassert(maxseq > 0);
-    HDassert(maxelem > 0);
-    HDassert(nseq);
-    HDassert(nelem);
-    HDassert(off);
-    HDassert(len);
-
-    /* Set the rank of the fastest changing dimension */
-    ndims = space->extent.rank;
-    fast_dim = (ndims - 1);
-
-    /* Get the pointers to the current span info and span nodes */
-    curr_span = iter->u.hyp.span[fast_dim];
-    abs_arr = iter->u.hyp.off;
-    off_arr = space->select.offset;
-    ispan = iter->u.hyp.span;
-    elem_size = iter->elmt_size;
-
-    /* Set the amount of elements to perform I/O on, etc. */
-    H5_CHECK_OVERFLOW(iter->elmt_left, hsize_t, size_t);
-    io_left = MIN(maxelem, (size_t)iter->elmt_left);
-    io_bytes_left = io_left * elem_size;
-
-    /* Compute the cumulative size of dataspace dimensions */
-    for(i = (int)fast_dim, acc = elem_size; i >= 0; i--) {
-        slab[i] = acc;
-        acc *= space->extent.size[i];
-    } /* end for */
-
-    /* Set the offset of the first element iterated on */
-    for(u = 0, loc_off = 0; u < ndims; u++)
-        /* Compute the sequential element offset */
-        loc_off += ((hsize_t)((hssize_t)abs_arr[u] + off_arr[u])) * slab[u];
-
-    /* Range check against number of elements left in selection */
-    HDassert(io_bytes_left <= (iter->elmt_left * elem_size));
-
-    /* Take care of any partial spans leftover from previous I/Os */
-    if(abs_arr[fast_dim]!=curr_span->low) {
-
-        /* Finish the span in the fastest changing dimension */
-
-        /* Compute the number of bytes to attempt in this span */
-        H5_CHECKED_ASSIGN(span_size, size_t, ((curr_span->high-abs_arr[fast_dim])+1)*elem_size, hsize_t);
-
-        /* Check number of bytes against upper bounds allowed */
-        if(span_size>io_bytes_left)
-            span_size=io_bytes_left;
-
-        /* Add the partial span to the list of sequences */
-        off[curr_seq]=loc_off;
-        len[curr_seq]=span_size;
-
-        /* Increment sequence count */
-        curr_seq++;
-
-        /* Set the location of the last span's end */
-        last_span_end=loc_off+span_size;
-
-        /* Decrement I/O left to perform */
-        io_bytes_left-=span_size;
+H5S__hyper_proj_int_build_proj(H5S_hyper_project_intersect_ud_t *udata) {
+    H5S_hyper_span_info_t *copied_span_info = NULL; /* Temporary span info pointer */
+    herr_t ret_value = SUCCEED; /* Return value */
 
-        /* Advance the hyperslab iterator */
-        /* Check if we are done */
-        if(io_bytes_left > 0) {
-            /* Move to next span in fastest changing dimension */
-            curr_span = curr_span->next;
+    FUNC_ENTER_STATIC
 
-            if(NULL != curr_span) {
-                /* Move location offset of destination */
-                loc_off += (curr_span->low - abs_arr[fast_dim]) * elem_size;
+    HDassert(udata->nelem > 0);
 
-                /* Move iterator for fastest changing dimension */
-                abs_arr[fast_dim] = curr_span->low;
-            } /* end if */
-        } /* end if */
-        else {
-            abs_arr[fast_dim] += span_size / elem_size;
+    /*
+     * Skip over skipped elements
+     */
+    if(udata->skip > 0) {
+        /* Work upwards, finishing each span tree before moving up */
+        HDassert(udata->ds_span[udata->depth]);
+        do {
+            /* Check for lowest dimension */
+            if(udata->ds_span[udata->depth]->down) {
+                if(udata->ds_low[udata->depth] <= udata->ds_span[udata->depth]->high) {
+                    /* If we will run out of elements to skip in this span,
+                     * advance to the first not fully skipped span and break
+                     * out of this loop (start moving downwards) */
+                    if(udata->skip < H5S__hyper_spans_nelem_helper(udata->ds_span[udata->depth]->down, 0, udata->op_gen)
+                            * (udata->ds_span[udata->depth]->high - udata->ds_low[udata->depth] + 1)) {
+                        udata->ds_low[udata->depth] += udata->skip / udata->ds_span[udata->depth]->down->op_info[0].u.nelmts;
+                        udata->skip %= udata->ds_span[udata->depth]->down->op_info[0].u.nelmts;
+                        break;
+                    } /* end if */
 
-            /* Check if we are still within the span */
-            if(abs_arr[fast_dim] <= curr_span->high) {
-                iter->u.hyp.span[fast_dim] = curr_span;
+                    /* Skip over this entire span */
+                    udata->skip -= udata->ds_span[udata->depth]->down->op_info[0].u.nelmts
+                            * (udata->ds_span[udata->depth]->high - udata->ds_low[udata->depth] + 1);
+                } /* end if */
             } /* end if */
-            /* If we walked off that span, advance to the next span */
             else {
-                /* Advance span in this dimension */
-                curr_span = curr_span->next;
-
-                /* Check if we have a valid span in this dimension still */
-                if(NULL != curr_span) {
-                    /* Reset absolute position */
-                    abs_arr[fast_dim] = curr_span->low;
-                    iter->u.hyp.span[fast_dim] = curr_span;
-                } /* end if */
-            } /* end else */
-        } /* end else */
-
-        /* Adjust iterator pointers */
-
-        if(NULL == curr_span) {
-/* Same as code in main loop */
-            /* Start at the next fastest dim */
-            curr_dim = (int)(fast_dim - 1);
-
-            /* Work back up through the dimensions */
-            while(curr_dim >= 0) {
-                /* Reset the current span */
-                curr_span = iter->u.hyp.span[curr_dim];
-
-                /* Increment absolute position */
-                abs_arr[curr_dim]++;
-
-                /* Check if we are still within the span */
-                if(abs_arr[curr_dim] <= curr_span->high) {
+                HDassert(udata->ds_rank - udata->depth == 1);
+
+                /* If we will run out of elements to skip in this span,
+                 * skip the remainder of the skipped elements and break out */
+                HDassert(udata->ds_low[udata->depth] <= udata->ds_span[udata->depth]->high);
+                if(udata->skip < (udata->ds_span[udata->depth]->high - udata->ds_low[udata->depth] + 1)) {
+                    udata->ds_low[udata->depth] += udata->skip;
+                    udata->skip = 0;
                     break;
                 } /* end if */
-                /* If we walked off that span, advance to the next span */
-                else {
-                    /* Advance span in this dimension */
-                    curr_span = curr_span->next;
 
-                    /* Check if we have a valid span in this dimension still */
-                    if(NULL != curr_span) {
-                        /* Reset the span in the current dimension */
-                        ispan[curr_dim] = curr_span;
+                /* Skip over this entire span */
+                udata->skip -= udata->ds_span[udata->depth]->high - udata->ds_low[udata->depth] + 1;
+            } /* end else */
 
-                        /* Reset absolute position */
-                        abs_arr[curr_dim] = curr_span->low;
+            /* Advance to next span */
+            udata->ds_span[udata->depth] = udata->ds_span[udata->depth]->next;
+            if(udata->ds_span[udata->depth])
+                udata->ds_low[udata->depth] = udata->ds_span[udata->depth]->low;
+            else if(udata->depth > 0) {
+                /* If present, append this span tree to the higher dimension's,
+                 * and release ownership of it */
+                if(udata->ps_span_info[udata->depth]) {
+                    if(H5S__hyper_append_span(&udata->ps_span_info[udata->depth - 1],
+                            udata->ds_rank - udata->depth + 1, udata->ds_low[udata->depth - 1],
+                            udata->ds_low[udata->depth - 1],
+                            udata->ps_span_info[udata->depth]) < 0)
+                        HGOTO_ERROR(H5E_DATASPACE, H5E_CANTAPPEND, FAIL, "can't allocate hyperslab span")
+                    H5S__hyper_free_span_info(udata->ps_span_info[udata->depth]);
+                    udata->ps_span_info[udata->depth] = NULL;
+                } /* end if */
 
+                /* Ran out of spans, move up one dimension */
+                udata->depth--;
+                HDassert(udata->ds_span[udata->depth]);
+                udata->ds_low[udata->depth]++;
+            } /* end if */
+            else
+                HGOTO_ERROR(H5E_DATASPACE, H5E_BADVALUE, FAIL, "insufficient elements in destination selection")
+        } while((udata->skip > 0)
+                || (udata->ds_low[udata->depth] > udata->ds_span[udata->depth]->high));
+
+        /* Work downwards until skip is 0 */
+        HDassert(udata->ds_span[udata->depth]);
+        while(udata->skip > 0) {
+            HDassert(udata->ds_span[udata->depth]->down);
+            udata->depth++;
+            udata->ds_span[udata->depth] = udata->ds_span[udata->depth - 1]->down->head;
+            udata->ds_low[udata->depth] = udata->ds_span[udata->depth]->low;
+            if(udata->ds_span[udata->depth]->down) {
+                do {
+                    /* If we will run out of elements to skip in this span,
+                     * advance to the first not fully skipped span and
+                     * continue down */
+                    if(udata->skip < H5S__hyper_spans_nelem_helper(udata->ds_span[udata->depth]->down, 0, udata->op_gen)
+                            * (udata->ds_span[udata->depth]->high - udata->ds_low[udata->depth] + 1)) {
+                        udata->ds_low[udata->depth] += udata->skip / udata->ds_span[udata->depth]->down->op_info[0].u.nelmts;
+                        udata->skip %= udata->ds_span[udata->depth]->down->op_info[0].u.nelmts;
                         break;
                     } /* end if */
-                    else {
-                        /* If we finished the span list in this dimension, decrement the dimension worked on and loop again */
-                        curr_dim--;
-                    } /* end else */
-                } /* end else */
-            } /* end while */
-
-            /* Check if we have more spans in the tree */
-            if(curr_dim >= 0) {
-                /* Walk back down the iterator positions, resetting them */
-                while((unsigned)curr_dim < fast_dim) {
-                    HDassert(curr_span);
-                    HDassert(curr_span->down);
-                    HDassert(curr_span->down->head);
-
-                    /* Increment current dimension */
-                    curr_dim++;
-
-                    /* Set the new span_info & span for this dimension */
-                    iter->u.hyp.span[curr_dim] = curr_span->down->head;
-
-                    /* Advance span down the tree */
-                    curr_span = curr_span->down->head;
-
-                    /* Reset the absolute offset for the dim */
-                    abs_arr[curr_dim] = curr_span->low;
-                } /* end while */
-
-                /* Verify that the curr_span points to the fastest dim */
-                HDassert(curr_span == iter->u.hyp.span[fast_dim]);
-
-                /* Reset the buffer offset */
-                for(u = 0, loc_off = 0; u < ndims; u++)
-                    loc_off += ((hsize_t)((hssize_t)abs_arr[u] + off_arr[u])) * slab[u];
-            } /* end else */
-            else
-                /* We had better be done with I/O or bad things are going to happen... */
-                HDassert(io_bytes_left == 0);
-        } /* end if */
-    } /* end if */
-
-    /* Perform the I/O on the elements, based on the position of the iterator */
-    while(io_bytes_left > 0 && curr_seq < maxseq) {
-        /* Sanity check */
-        HDassert(curr_span);
-
-        /* Adjust location offset of destination to compensate for initial increment below */
-        loc_off -= curr_span->pstride;
 
-        /* Loop over all the spans in the fastest changing dimension */
-        while(curr_span != NULL) {
-            /* Move location offset of destination */
-            loc_off += curr_span->pstride;
-
-            /* Compute the number of elements to attempt in this span */
-            H5_CHECKED_ASSIGN(span_size, size_t, curr_span->nelem, hsize_t);
-
-            /* Check number of elements against upper bounds allowed */
-            if(span_size >= io_bytes_left) {
-                /* Trim the number of bytes to output */
-                span_size = io_bytes_left;
-                io_bytes_left = 0;
-
-/* COMMON */
-                /* Store the I/O information for the span */
+                    /* Skip over this entire span */
+                    udata->skip -= udata->ds_span[udata->depth]->down->op_info[0].u.nelmts
+                            * (udata->ds_span[udata->depth]->high - udata->ds_low[udata->depth] + 1);
 
-                /* Check if this is appending onto previous sequence */
-                if(curr_seq > 0 && last_span_end == loc_off)
-                    len[curr_seq - 1] += span_size;
-                else {
-                    off[curr_seq] = loc_off;
-                    len[curr_seq] = span_size;
-
-                    /* Increment the number of sequences in arrays */
-                    curr_seq++;
-                } /* end else */
-
-                /* Set the location of the last span's end */
-                last_span_end = loc_off + span_size;
-/* end COMMON */
-
-                /* Break out now, we are finished with I/O */
-                break;
+                    /* Advance to next span */
+                    udata->ds_span[udata->depth] = udata->ds_span[udata->depth]->next;
+                    HDassert(udata->ds_span[udata->depth]);
+                    udata->ds_low[udata->depth] = udata->ds_span[udata->depth]->low;
+                } while(udata->skip > 0);
             } /* end if */
             else {
-                /* Decrement I/O left to perform */
-                io_bytes_left -= span_size;
-
-/* COMMON */
-                /* Store the I/O information for the span */
-
-                /* Check if this is appending onto previous sequence */
-                if(curr_seq > 0 && last_span_end == loc_off)
-                    len[curr_seq-1]+=span_size;
-                else {
-                    off[curr_seq] = loc_off;
-                    len[curr_seq] = span_size;
-
-                    /* Increment the number of sequences in arrays */
-                    curr_seq++;
-                } /* end else */
+                do {
+                    /* If we will run out of elements to skip in this span,
+                     * skip the remainder of the skipped elements */
+                    if(udata->skip < (udata->ds_span[udata->depth]->high - udata->ds_low[udata->depth] + 1)) {
+                        udata->ds_low[udata->depth] += udata->skip;
+                        udata->skip = 0;
+                        break;
+                    } /* end if */
 
-                /* Set the location of the last span's end */
-                last_span_end = loc_off + span_size;
-/* end COMMON */
+                    /* Skip over this entire span */
+                    udata->skip -= udata->ds_span[udata->depth]->high - udata->ds_low[udata->depth] + 1;
 
-                /* If the sequence & offset arrays are full, do what? */
-                if(curr_seq >= maxseq) {
-                    /* Break out now, we are finished with sequences */
-                    break;
-                } /* end else */
+                    /* Advance to next span */
+                    udata->ds_span[udata->depth] = udata->ds_span[udata->depth]->next;
+                    HDassert(udata->ds_span[udata->depth]);
+                    udata->ds_low[udata->depth] = udata->ds_span[udata->depth]->low;
+                } while(udata->skip > 0);
             } /* end else */
-
-	    /* Move to next span in fastest changing dimension */
-	    curr_span=curr_span->next;
         } /* end while */
+    } /* end if */
 
-        /* Check if we are done */
-        if(io_bytes_left==0 || curr_seq>=maxseq) {
-            HDassert(curr_span);
-            abs_arr[fast_dim]=curr_span->low+(span_size/elem_size);
-
-            /* Check if we are still within the span */
-            if(abs_arr[fast_dim]<=curr_span->high) {
-                iter->u.hyp.span[fast_dim]=curr_span;
-                break;
-            } /* end if */
-            /* If we walked off that span, advance to the next span */
-            else {
-                /* Advance span in this dimension */
-                curr_span=curr_span->next;
-
-                /* Check if we have a valid span in this dimension still */
-                if(curr_span!=NULL) {
-                    /* Reset absolute position */
-                    abs_arr[fast_dim]=curr_span->low;
-                    iter->u.hyp.span[fast_dim]=curr_span;
+    /*
+     * Add requested number of elements to projected space
+     */
+    /* Work upwards, adding all elements of each span tree until it can't fit
+     * all elements */
+    HDassert(udata->ds_span[udata->depth]);
+    do {
+        /* Check for lowest dimension */
+        if(udata->ds_span[udata->depth]->down) {
+            if(udata->ds_low[udata->depth] <= udata->ds_span[udata->depth]->high) {
+                /* If we will run out of elements to add in this span, add
+                 * any complete spans, advance to the first not fully added
+                 * span, and break out of this loop (start moving downwards)
+                 */
+                if(udata->nelem < H5S__hyper_spans_nelem_helper(udata->ds_span[udata->depth]->down, 0, udata->op_gen)
+                        * (udata->ds_span[udata->depth]->high - udata->ds_low[udata->depth] + 1)) {
+                    if(udata->nelem >= udata->ds_span[udata->depth]->down->op_info[0].u.nelmts) {
+                        if(udata->share_selection) {
+                            if(H5S__hyper_append_span(&udata->ps_span_info[udata->depth],
+                                    udata->ds_rank - udata->depth, udata->ds_low[udata->depth],
+                                    udata->ds_low[udata->depth] + (udata->nelem / udata->ds_span[udata->depth]->down->op_info[0].u.nelmts) - 1,
+                                    udata->ds_span[udata->depth]->down) < 0)
+                                HGOTO_ERROR(H5E_DATASPACE, H5E_CANTAPPEND, FAIL, "can't allocate hyperslab span")
+                        } /* end if */
+                        else {
+                            /* If we're not sharing the destination space's
+                             * spans, we must copy it first (then release it
+                             * afterwards) */
+                            if(NULL == (copied_span_info = H5S__hyper_copy_span_helper(udata->ds_span[udata->depth]->down, udata->ds_rank - udata->depth, 1, udata->op_gen)))
+                                HGOTO_ERROR(H5E_DATASPACE, H5E_CANTCOPY, FAIL, "can't copy destination spans")
+                            if(H5S__hyper_append_span(&udata->ps_span_info[udata->depth],
+                                    udata->ds_rank - udata->depth, udata->ds_low[udata->depth],
+                                    udata->ds_low[udata->depth] + (udata->nelem / udata->ds_span[udata->depth]->down->op_info[0].u.nelmts) - 1,
+                                    copied_span_info) < 0)
+                                HGOTO_ERROR(H5E_DATASPACE, H5E_CANTAPPEND, FAIL, "can't allocate hyperslab span")
+                            H5S__hyper_free_span_info(copied_span_info);
+                            copied_span_info = NULL;
+                        } /* end else */
+                        udata->ds_low[udata->depth] += udata->nelem / udata->ds_span[udata->depth]->down->op_info[0].u.nelmts;
+                        udata->nelem %= udata->ds_span[udata->depth]->down->op_info[0].u.nelmts;
+                    } /* end if */
                     break;
                 } /* end if */
-            } /* end else */
-        } /* end if */
-
-        /* Adjust iterator pointers */
-
-        /* Start at the next fastest dim */
-        curr_dim = (int)(fast_dim - 1);
-
-        /* Work back up through the dimensions */
-        while(curr_dim >= 0) {
-            /* Reset the current span */
-	    curr_span=iter->u.hyp.span[curr_dim];
-
-            /* Increment absolute position */
-            abs_arr[curr_dim]++;
-
-            /* Check if we are still within the span */
-            if(abs_arr[curr_dim]<=curr_span->high) {
-                break;
-            } /* end if */
-            /* If we walked off that span, advance to the next span */
-            else {
-                /* Advance span in this dimension */
-                curr_span=curr_span->next;
 
-                /* Check if we have a valid span in this dimension still */
-                if(curr_span!=NULL) {
-                    /* Reset the span in the current dimension */
-                    ispan[curr_dim]=curr_span;
-
-                    /* Reset absolute position */
-                    abs_arr[curr_dim]=curr_span->low;
-
-                    break;
+                /* Append span tree for entire span */
+                if(udata->share_selection) {
+                    if(H5S__hyper_append_span(&udata->ps_span_info[udata->depth],
+                            udata->ds_rank - udata->depth, udata->ds_low[udata->depth],
+                            udata->ds_span[udata->depth]->high,
+                            udata->ds_span[udata->depth]->down) < 0)
+                        HGOTO_ERROR(H5E_DATASPACE, H5E_CANTAPPEND, FAIL, "can't allocate hyperslab span")
                 } /* end if */
                 else {
-                    /* If we finished the span list in this dimension, decrement the dimension worked on and loop again */
-                    curr_dim--;
+                    /* If we're not sharing the destination space's
+                     * spans, we must copy it first (then release it
+                     * afterwards) */
+                    if(NULL == (copied_span_info = H5S__hyper_copy_span_helper(udata->ds_span[udata->depth]->down, udata->ds_rank - udata->depth, 1, udata->op_gen)))
+                        HGOTO_ERROR(H5E_DATASPACE, H5E_CANTCOPY, FAIL, "can't copy destination spans")
+                    if(H5S__hyper_append_span(&udata->ps_span_info[udata->depth],
+                            udata->ds_rank - udata->depth, udata->ds_low[udata->depth],
+                            udata->ds_span[udata->depth]->high,
+                            copied_span_info) < 0)
+                        HGOTO_ERROR(H5E_DATASPACE, H5E_CANTAPPEND, FAIL, "can't allocate hyperslab span")
+                    H5S__hyper_free_span_info(copied_span_info);
+                    copied_span_info = NULL;
                 } /* end else */
-            } /* end else */
-        } /* end while */
-
-        /* Check if we are finished with the spans in the tree */
-        if(curr_dim < 0) {
-            /* We had better be done with I/O or bad things are going to happen... */
-            HDassert(io_bytes_left == 0);
-            break;
+                udata->nelem -= udata->ds_span[udata->depth]->down->op_info[0].u.nelmts
+                        * (udata->ds_span[udata->depth]->high - udata->ds_low[udata->depth] + 1);
+            } /* end if */
         } /* end if */
         else {
-            /* Walk back down the iterator positions, resetting them */
-            while((unsigned)curr_dim < fast_dim) {
-                HDassert(curr_span);
-                HDassert(curr_span->down);
-                HDassert(curr_span->down->head);
-
-                /* Increment current dimension to the next dimension down */
-                curr_dim++;
-
-                /* Set the new span for the next dimension down */
-                iter->u.hyp.span[curr_dim] = curr_span->down->head;
-
-                /* Advance span down the tree */
-                curr_span = curr_span->down->head;
-
-                /* Reset the absolute offset for the dim */
-                abs_arr[curr_dim] = curr_span->low;
-            } /* end while */
+            HDassert(udata->ds_rank - udata->depth == 1);
+
+            /* If we will run out of elements to add in this span, add the
+             * remainder of the elements and break out */
+            HDassert(udata->ds_low[udata->depth] <= udata->ds_span[udata->depth]->high);
+            if(udata->nelem < (udata->ds_span[udata->depth]->high - udata->ds_low[udata->depth] + 1)) {
+                if(H5S__hyper_append_span(&udata->ps_span_info[udata->depth], 1,
+                        udata->ds_low[udata->depth], udata->ds_low[udata->depth] + udata->nelem - 1, NULL) < 0)
+                    HGOTO_ERROR(H5E_DATASPACE, H5E_CANTAPPEND, FAIL, "can't allocate hyperslab span")
+                udata->ds_low[udata->depth] += udata->nelem;
+                udata->nelem = 0;
+                break;
+            } /* end if */
 
-            /* Verify that the curr_span points to the fastest dim */
-            HDassert(curr_span == iter->u.hyp.span[fast_dim]);
+            /* Append span tree for entire span */
+            if(H5S__hyper_append_span(&udata->ps_span_info[udata->depth], 1,
+                    udata->ds_low[udata->depth], udata->ds_span[udata->depth]->high, NULL) < 0)
+                    HGOTO_ERROR(H5E_DATASPACE, H5E_CANTAPPEND, FAIL, "can't allocate hyperslab span")
+            udata->nelem -= udata->ds_span[udata->depth]->high - udata->ds_low[udata->depth] + 1;
         } /* end else */
 
-        /* Reset the buffer offset */
-        for(u = 0, loc_off = 0; u < ndims; u++)
-            loc_off += ((hsize_t)((hssize_t)abs_arr[u] + off_arr[u])) * slab[u];
-    } /* end while */
-
-    /* Decrement number of elements left in iterator */
-    io_used = (io_left - (io_bytes_left / elem_size));
-    iter->elmt_left -= io_used;
-
-    /* Set the number of sequences generated */
-    *nseq = curr_seq;
-
-    /* Set the number of elements used */
-    *nelem = io_used;
-
-    FUNC_LEAVE_NOAPI(SUCCEED)
-} /* end H5S__hyper_get_seq_list_gen() */
-
-
-/*--------------------------------------------------------------------------
- NAME
-    H5S__hyper_get_seq_list_opt
- PURPOSE
-    Create a list of offsets & lengths for a selection
- USAGE
-    herr_t H5S_select_hyper_get_file_list_opt(space,iter,maxseq,maxelem,nseq,nelem,off,len)
-        H5S_t *space;           IN: Dataspace containing selection to use.
-        H5S_sel_iter_t *iter;   IN/OUT: Selection iterator describing last
-                                    position of interest in selection.
-        size_t maxseq;          IN: Maximum number of sequences to generate
-        size_t maxelem;         IN: Maximum number of elements to include in the
-                                    generated sequences
-        size_t *nseq;           OUT: Actual number of sequences generated
-        size_t *nelem;          OUT: Actual number of elements in sequences generated
-        hsize_t *off;           OUT: Array of offsets
-        size_t *len;            OUT: Array of lengths
- RETURNS
-    Non-negative on success/Negative on failure.
- DESCRIPTION
-    Use the selection in the dataspace to generate a list of byte offsets and
-    lengths for the region(s) selected.  Start/Restart from the position in the
-    ITER parameter.  The number of sequences generated is limited by the MAXSEQ
-    parameter and the number of sequences actually generated is stored in the
-    NSEQ parameter.
- GLOBAL VARIABLES
- COMMENTS, BUGS, ASSUMPTIONS
- EXAMPLES
- REVISION LOG
---------------------------------------------------------------------------*/
-static herr_t
-H5S__hyper_get_seq_list_opt(const H5S_t *space, H5S_sel_iter_t *iter,
-    size_t maxseq, size_t maxelem, size_t *nseq, size_t *nelem,
-    hsize_t *off, size_t *len)
-{
-    hsize_t *mem_size;                  /* Size of the source buffer */
-    hsize_t slab[H5S_MAX_RANK];     /* Hyperslab size */
-    const hssize_t *sel_off;            /* Selection offset in dataspace */
-    hsize_t offset[H5S_MAX_RANK];   /* Coordinate offset in dataspace */
-    hsize_t tmp_count[H5S_MAX_RANK];/* Temporary block count */
-    hsize_t tmp_block[H5S_MAX_RANK];/* Temporary block offset */
-    hsize_t wrap[H5S_MAX_RANK];     /* Bytes to wrap around at the end of a row */
-    hsize_t skip[H5S_MAX_RANK];     /* Bytes to skip between blocks */
-    const H5S_hyper_dim_t *tdiminfo;    /* Temporary pointer to diminfo information */
-    hsize_t fast_dim_start,    /* Local copies of fastest changing dimension info */
-        fast_dim_stride,
-        fast_dim_block,
-        fast_dim_offset;
-    size_t fast_dim_buf_off;    /* Local copy of amount to move fastest dimension buffer offset */
-    size_t fast_dim_count;      /* Number of blocks left in fastest changing dimension */
-    size_t tot_blk_count;       /* Total number of blocks left to output */
-    size_t act_blk_count;       /* Actual number of blocks to output */
-    size_t total_rows;          /* Total number of entire rows to output */
-    size_t curr_rows;           /* Current number of entire rows to output */
-    unsigned fast_dim;  /* Rank of the fastest changing dimension for the dataspace */
-    unsigned ndims;     /* Number of dimensions of dataset */
-    int temp_dim;       /* Temporary rank holder */
-    hsize_t acc;	/* Accumulator */
-    hsize_t loc;        /* Coordinate offset */
-    size_t curr_seq = 0; /* Current sequence being operated on */
-    size_t actual_elem; /* The actual number of elements to count */
-    size_t actual_bytes;/* The actual number of bytes to copy */
-    size_t io_left;     /* The number of elements left in I/O operation */
-    size_t start_io_left; /* The initial number of elements left in I/O operation */
-    size_t elem_size;   /* Size of each element iterating over */
-    unsigned u;         /* Local index variable */
-    int i;              /* Local index variable */
-
-    FUNC_ENTER_STATIC_NOERR
-
-    /* Check args */
-    HDassert(space);
-    HDassert(iter);
-    HDassert(maxseq > 0);
-    HDassert(maxelem > 0);
-    HDassert(nseq);
-    HDassert(nelem);
-    HDassert(off);
-    HDassert(len);
-
-    /* Set the local copy of the diminfo pointer */
-    tdiminfo = iter->u.hyp.diminfo;
-
-    /* Check if this is a "flattened" regular hyperslab selection */
-    if(iter->u.hyp.iter_rank != 0 && iter->u.hyp.iter_rank < space->extent.rank) {
-        /* Set the aliases for a few important dimension ranks */
-        ndims = iter->u.hyp.iter_rank;
-        fast_dim = ndims - 1;
-
-        /* Set the local copy of the selection offset */
-        sel_off = iter->u.hyp.sel_off;
-
-        /* Set up the pointer to the size of the memory space */
-        mem_size = iter->u.hyp.size;
-    } /* end if */
-    else {
-        /* Set the aliases for a few important dimension ranks */
-        ndims = space->extent.rank;
-        fast_dim = ndims - 1;
-
-        /* Set the local copy of the selection offset */
-        sel_off = space->select.offset;
-
-        /* Set up the pointer to the size of the memory space */
-        mem_size = space->extent.size;
-    } /* end else */
-
-    /* initialize row sizes for each dimension */
-    elem_size = iter->elmt_size;
-    for(i = (int)fast_dim, acc = elem_size; i >= 0; i--) {
-        slab[i] = acc;
-        acc *= mem_size[i];
-    } /* end for */
-
-    /* Calculate the number of elements to sequence through */
-    H5_CHECK_OVERFLOW(iter->elmt_left, hsize_t, size_t);
-    io_left = MIN((size_t)iter->elmt_left, maxelem);
-
-    /* Sanity check that there aren't any "remainder" sequences in process */
-    HDassert(!((iter->u.hyp.off[fast_dim] - tdiminfo[fast_dim].start) % tdiminfo[fast_dim].stride != 0 ||
-            ((iter->u.hyp.off[fast_dim] != tdiminfo[fast_dim].start) && tdiminfo[fast_dim].count == 1)));
-
-    /* We've cleared the "remainder" of the previous fastest dimension
-     * sequence before calling this routine, so we must be at the beginning of
-     * a sequence.  Use the fancy algorithm to compute the offsets and run
-     * through as many as possible, until the buffer fills up.
-     */
-
-    /* Keep the number of elements we started with */
-    start_io_left = io_left;
-
-    /* Compute the arrays to perform I/O on */
-
-    /* Copy the location of the point to get */
-    /* (Add in the selection offset) */
-    for(u = 0; u < ndims; u++)
-        offset[u] = (hsize_t)((hssize_t)iter->u.hyp.off[u] + sel_off[u]);
+        /* Advance to next span */
+        udata->ds_span[udata->depth] = udata->ds_span[udata->depth]->next;
+        if(udata->ds_span[udata->depth])
+            udata->ds_low[udata->depth] = udata->ds_span[udata->depth]->low;
+        else if(udata->depth > 0) {
+            /* Append this span tree to the higher dimension's, and release
+             * ownership of it */
+            HDassert(udata->ps_span_info[udata->depth]);
+            if(H5S__hyper_append_span(&udata->ps_span_info[udata->depth - 1],
+                    udata->ds_rank - udata->depth + 1, udata->ds_low[udata->depth - 1],
+                    udata->ds_low[udata->depth - 1],
+                    udata->ps_span_info[udata->depth]) < 0)
+                HGOTO_ERROR(H5E_DATASPACE, H5E_CANTAPPEND, FAIL, "can't allocate hyperslab span")
+            H5S__hyper_free_span_info(udata->ps_span_info[udata->depth]);
+            udata->ps_span_info[udata->depth] = NULL;
 
-    /* Compute the current "counts" for this location */
-    for(u = 0; u < ndims; u++) {
-        if(tdiminfo[u].count == 1) {
-            tmp_count[u] = 0;
-            tmp_block[u] = iter->u.hyp.off[u] - tdiminfo[u].start;
+            /* Ran out of spans, move up one dimension */
+            udata->depth--;
+            HDassert(udata->ds_span[udata->depth]);
+            udata->ds_low[udata->depth]++;
         } /* end if */
         else {
-            tmp_count[u] = (iter->u.hyp.off[u] - tdiminfo[u].start) / tdiminfo[u].stride;
-            tmp_block[u] = (iter->u.hyp.off[u] - tdiminfo[u].start) % tdiminfo[u].stride;
+            /* We have finished the entire destination span tree.  If there are
+             * still elements to add, issue an error. */
+            if(udata->nelem > 0)
+                HGOTO_ERROR(H5E_DATASPACE, H5E_BADVALUE, FAIL, "insufficient elements in destination selection")
+            break;
         } /* end else */
-    } /* end for */
-
-    /* Compute the initial buffer offset */
-    for(u = 0, loc = 0; u < ndims; u++)
-        loc += offset[u] * slab[u];
-
-    /* Set the number of elements to write each time */
-    H5_CHECKED_ASSIGN(actual_elem, size_t, tdiminfo[fast_dim].block, hsize_t);
-
-    /* Set the number of actual bytes */
-    actual_bytes = actual_elem * elem_size;
-
-    /* Set local copies of information for the fastest changing dimension */
-    fast_dim_start = tdiminfo[fast_dim].start;
-    fast_dim_stride = tdiminfo[fast_dim].stride;
-    fast_dim_block = tdiminfo[fast_dim].block;
-    H5_CHECKED_ASSIGN(fast_dim_buf_off, size_t, slab[fast_dim] * fast_dim_stride, hsize_t);
-    fast_dim_offset = (hsize_t)((hssize_t)fast_dim_start + sel_off[fast_dim]);
-
-    /* Compute the number of blocks which would fit into the buffer */
-    H5_CHECK_OVERFLOW(io_left / fast_dim_block, hsize_t, size_t);
-    tot_blk_count = (size_t)(io_left / fast_dim_block);
-
-    /* Don't go over the maximum number of sequences allowed */
-    tot_blk_count = MIN(tot_blk_count, (maxseq - curr_seq));
-
-    /* Compute the amount to wrap at the end of each row */
-    for(u = 0; u < ndims; u++)
-        wrap[u] = (mem_size[u] - (tdiminfo[u].stride * tdiminfo[u].count)) * slab[u];
-
-    /* Compute the amount to skip between blocks */
-    for(u = 0; u < ndims; u++)
-        skip[u] = (tdiminfo[u].stride - tdiminfo[u].block) * slab[u];
-
-    /* Check if there is a partial row left (with full blocks) */
-    if(tmp_count[fast_dim] > 0) {
-        /* Get number of blocks in fastest dimension */
-        H5_CHECKED_ASSIGN(fast_dim_count, size_t, tdiminfo[fast_dim].count - tmp_count[fast_dim], hsize_t);
-
-        /* Make certain this entire row will fit into buffer */
-        fast_dim_count = MIN(fast_dim_count, tot_blk_count);
-
-        /* Number of blocks to sequence over */
-        act_blk_count = fast_dim_count;
-
-        /* Loop over all the blocks in the fastest changing dimension */
-        while(fast_dim_count > 0) {
-            /* Store the sequence information */
-            off[curr_seq] = loc;
-            len[curr_seq] = actual_bytes;
-
-            /* Increment sequence count */
-            curr_seq++;
-
-            /* Increment information to reflect block just processed */
-            loc += fast_dim_buf_off;
-
-            /* Decrement number of blocks */
-            fast_dim_count--;
-        } /* end while */
-
-        /* Decrement number of elements left */
-        io_left -= actual_elem * act_blk_count;
-
-        /* Decrement number of blocks left */
-        tot_blk_count -= act_blk_count;
-
-        /* Increment information to reflect block just processed */
-        tmp_count[fast_dim] += act_blk_count;
-
-        /* Check if we finished the entire row of blocks */
-        if(tmp_count[fast_dim] >= tdiminfo[fast_dim].count) {
-            /* Increment offset in destination buffer */
-            loc += wrap[fast_dim];
-
-            /* Increment information to reflect block just processed */
-            offset[fast_dim] = fast_dim_offset;    /* reset the offset in the fastest dimension */
-            tmp_count[fast_dim] = 0;
-
-            /* Increment the offset and count for the other dimensions */
-            temp_dim = (int)fast_dim - 1;
-            while(temp_dim >= 0) {
-                /* Move to the next row in the curent dimension */
-                offset[temp_dim]++;
-                tmp_block[temp_dim]++;
-
-                /* If this block is still in the range of blocks to output for the dimension, break out of loop */
-                if(tmp_block[temp_dim] < tdiminfo[temp_dim].block)
+    } while((udata->nelem > 0)
+            || (udata->ds_low[udata->depth] > udata->ds_span[udata->depth]->high));
+
+    /* Work downwards until nelem is 0 */
+    HDassert(udata->ds_span[udata->depth] || (udata->nelem == 0));
+    while(udata->nelem > 0) {
+        HDassert(udata->ds_span[udata->depth]->down);
+        udata->depth++;
+        udata->ds_span[udata->depth] = udata->ds_span[udata->depth - 1]->down->head;
+        udata->ds_low[udata->depth] = udata->ds_span[udata->depth]->low;
+        if(udata->ds_span[udata->depth]->down) {
+            do {
+                /* If we will run out of elements to add in this span, add
+                 * any complete spans, advance to the first not fully added
+                 * span and continue down
+                 */
+                HDassert(udata->ds_low[udata->depth] <= udata->ds_span[udata->depth]->high);
+                if(udata->nelem < H5S__hyper_spans_nelem_helper(udata->ds_span[udata->depth]->down, 0, udata->op_gen)
+                        * (udata->ds_span[udata->depth]->high - udata->ds_low[udata->depth] + 1)) {
+                    if(udata->nelem >= udata->ds_span[udata->depth]->down->op_info[0].u.nelmts) {
+                        if(udata->share_selection) {
+                            if(H5S__hyper_append_span(&udata->ps_span_info[udata->depth],
+                                    udata->ds_rank - udata->depth, udata->ds_low[udata->depth],
+                                    udata->ds_low[udata->depth] + (udata->nelem / udata->ds_span[udata->depth]->down->op_info[0].u.nelmts) - 1,
+                                    udata->ds_span[udata->depth]->down) < 0)
+                                HGOTO_ERROR(H5E_DATASPACE, H5E_CANTAPPEND, FAIL, "can't allocate hyperslab span")
+                        } /* end if */
+                        else {
+                            /* If we're not sharing the destination space's
+                             * spans, we must copy it first (then release it
+                             * afterwards) */
+                            if(NULL == (copied_span_info = H5S__hyper_copy_span_helper(udata->ds_span[udata->depth]->down, udata->ds_rank - udata->depth, 1, udata->op_gen)))
+                                HGOTO_ERROR(H5E_DATASPACE, H5E_CANTCOPY, FAIL, "can't copy destination spans")
+                            if(H5S__hyper_append_span(&udata->ps_span_info[udata->depth],
+                                    udata->ds_rank - udata->depth, udata->ds_low[udata->depth],
+                                    udata->ds_low[udata->depth] + (udata->nelem / udata->ds_span[udata->depth]->down->op_info[0].u.nelmts) - 1,
+                                    copied_span_info) < 0)
+                                HGOTO_ERROR(H5E_DATASPACE, H5E_CANTAPPEND, FAIL, "can't allocate hyperslab span")
+                            H5S__hyper_free_span_info(copied_span_info);
+                            copied_span_info = NULL;
+                        } /* end else */
+                        udata->ds_low[udata->depth] += udata->nelem / udata->ds_span[udata->depth]->down->op_info[0].u.nelmts;
+                        udata->nelem %= udata->ds_span[udata->depth]->down->op_info[0].u.nelmts;
+                    } /* end if */
                     break;
-                else {
-                    /* Move to the next block in the current dimension */
-                    offset[temp_dim] += (tdiminfo[temp_dim].stride - tdiminfo[temp_dim].block);
-                    loc += skip[temp_dim];
-                    tmp_block[temp_dim] = 0;
-                    tmp_count[temp_dim]++;
+                } /* end if */
 
-                    /* If this block is still in the range of blocks to output for the dimension, break out of loop */
-                    if(tmp_count[temp_dim] < tdiminfo[temp_dim].count)
-                        break;
-                    else {
-                        offset[temp_dim] = (hsize_t)((hssize_t)tdiminfo[temp_dim].start + sel_off[temp_dim]);
-                        loc += wrap[temp_dim];
-                        tmp_count[temp_dim] = 0; /* reset back to the beginning of the line */
-                        tmp_block[temp_dim] = 0;
-                    } /* end else */
+                /* Append span tree for entire span */
+                if(udata->share_selection) {
+                    if(H5S__hyper_append_span(&udata->ps_span_info[udata->depth],
+                            udata->ds_rank - udata->depth, udata->ds_low[udata->depth],
+                            udata->ds_span[udata->depth]->high,
+                            udata->ds_span[udata->depth]->down) < 0)
+                        HGOTO_ERROR(H5E_DATASPACE, H5E_CANTAPPEND, FAIL, "can't allocate hyperslab span")
+                } /* end if */
+                else {
+                    /* If we're not sharing the destination space's
+                     * spans, we must copy it first (then release it
+                     * afterwards) */
+                    if(NULL == (copied_span_info = H5S__hyper_copy_span_helper(udata->ds_span[udata->depth]->down, udata->ds_rank - udata->depth, 1, udata->op_gen)))
+                        HGOTO_ERROR(H5E_DATASPACE, H5E_CANTCOPY, FAIL, "can't copy destination spans")
+                    if(H5S__hyper_append_span(&udata->ps_span_info[udata->depth],
+                            udata->ds_rank - udata->depth, udata->ds_low[udata->depth],
+                            udata->ds_span[udata->depth]->high,
+                            copied_span_info) < 0)
+                        HGOTO_ERROR(H5E_DATASPACE, H5E_CANTAPPEND, FAIL, "can't allocate hyperslab span")
+                    H5S__hyper_free_span_info(copied_span_info);
+                    copied_span_info = NULL;
                 } /* end else */
-
-                /* Decrement dimension count */
-                temp_dim--;
-            } /* end while */
+                udata->nelem -= udata->ds_span[udata->depth]->down->op_info[0].u.nelmts
+                        * (udata->ds_span[udata->depth]->high - udata->ds_low[udata->depth] + 1);
+
+                /* Advance to next span */
+                udata->ds_span[udata->depth] = udata->ds_span[udata->depth]->next;
+                HDassert(udata->ds_span[udata->depth]);
+                udata->ds_low[udata->depth] = udata->ds_span[udata->depth]->low;
+            } while(udata->nelem > 0);
         } /* end if */
         else {
-            /* Update the offset in the fastest dimension */
-            offset[fast_dim] += (fast_dim_stride * act_blk_count);
-        } /* end else */
-    } /* end if */
-
-    /* Compute the number of entire rows to read in */
-    H5_CHECK_OVERFLOW(tot_blk_count / tdiminfo[fast_dim].count, hsize_t, size_t);
-    curr_rows = total_rows = (size_t)(tot_blk_count / tdiminfo[fast_dim].count);
-
-    /* Reset copy of number of blocks in fastest dimension */
-    H5_CHECKED_ASSIGN(fast_dim_count, size_t, tdiminfo[fast_dim].count, hsize_t);
-
-    /* Read in data until an entire sequence can't be written out any longer */
-    while(curr_rows > 0) {
-
-#define DUFF_GUTS                                                       \
-/* Store the sequence information */                                    \
-off[curr_seq] = loc;                                                    \
-len[curr_seq] = actual_bytes;                                           \
-                                                                        \
-/* Increment sequence count */                                          \
-curr_seq++;                                                             \
-                                                                        \
-/* Increment information to reflect block just processed */             \
-loc += fast_dim_buf_off;
-
-#ifdef NO_DUFFS_DEVICE
-        /* Loop over all the blocks in the fastest changing dimension */
-        while(fast_dim_count > 0) {
-            DUFF_GUTS
-
-            /* Decrement number of blocks */
-            fast_dim_count--;
-        } /* end while */
-#else /* NO_DUFFS_DEVICE */
-        {
-            size_t duffs_index; /* Counting index for Duff's device */
-
-            duffs_index = (fast_dim_count + 7) / 8;
-            switch (fast_dim_count % 8) {
-                default:
-                    HDassert(0 && "This Should never be executed!");
-                    break;
-                case 0:
-                    do
-                      {
-                        DUFF_GUTS
-                        H5_ATTR_FALLTHROUGH
-                case 7:
-                        DUFF_GUTS
-                        H5_ATTR_FALLTHROUGH
-                case 6:
-                        DUFF_GUTS
-                        H5_ATTR_FALLTHROUGH
-                case 5:
-                        DUFF_GUTS
-                        H5_ATTR_FALLTHROUGH
-                case 4:
-                        DUFF_GUTS
-                        H5_ATTR_FALLTHROUGH
-                case 3:
-                        DUFF_GUTS
-                        H5_ATTR_FALLTHROUGH
-                case 2:
-                        DUFF_GUTS
-                        H5_ATTR_FALLTHROUGH
-                case 1:
-                        DUFF_GUTS
-                  } while (--duffs_index > 0);
-            } /* end switch */
-        }
-#endif /* NO_DUFFS_DEVICE */
-#undef DUFF_GUTS
-
-        /* Increment offset in destination buffer */
-        loc += wrap[fast_dim];
-
-        /* Increment the offset and count for the other dimensions */
-        temp_dim = (int)fast_dim - 1;
-        while(temp_dim >= 0) {
-            /* Move to the next row in the curent dimension */
-            offset[temp_dim]++;
-            tmp_block[temp_dim]++;
-
-            /* If this block is still in the range of blocks to output for the dimension, break out of loop */
-            if(tmp_block[temp_dim] < tdiminfo[temp_dim].block)
-                break;
-            else {
-                /* Move to the next block in the current dimension */
-                offset[temp_dim] += (tdiminfo[temp_dim].stride - tdiminfo[temp_dim].block);
-                loc += skip[temp_dim];
-                tmp_block[temp_dim] = 0;
-                tmp_count[temp_dim]++;
-
-                /* If this block is still in the range of blocks to output for the dimension, break out of loop */
-                if(tmp_count[temp_dim] < tdiminfo[temp_dim].count)
+            HDassert(udata->ds_rank - udata->depth == 1);
+            do {
+                /* If we will run out of elements to add in this span, add
+                 * the remainder of the elements and break out */
+                HDassert(udata->ds_low[udata->depth] <= udata->ds_span[udata->depth]->high);
+                if(udata->nelem < (udata->ds_span[udata->depth]->high - udata->ds_low[udata->depth] + 1)) {
+                    if(H5S__hyper_append_span(&udata->ps_span_info[udata->depth], 1,
+                            udata->ds_low[udata->depth], udata->ds_low[udata->depth] + udata->nelem - 1, NULL) < 0)
+                        HGOTO_ERROR(H5E_DATASPACE, H5E_CANTAPPEND, FAIL, "can't allocate hyperslab span")
+                    udata->ds_low[udata->depth] += udata->nelem;
+                    udata->nelem = 0;
                     break;
-                else {
-                    offset[temp_dim] = (hsize_t)((hssize_t)tdiminfo[temp_dim].start + sel_off[temp_dim]);
-                    loc += wrap[temp_dim];
-                    tmp_count[temp_dim] = 0; /* reset back to the beginning of the line */
-                    tmp_block[temp_dim] = 0;
-                } /* end else */
-            } /* end else */
-
-            /* Decrement dimension count */
-            temp_dim--;
-        } /* end while */
+                } /* end if */
 
-        /* Decrement the number of rows left */
-        curr_rows--;
+                /* Append span tree for entire span */
+                if(H5S__hyper_append_span(&udata->ps_span_info[udata->depth], 1,
+                        udata->ds_low[udata->depth], udata->ds_span[udata->depth]->high, NULL) < 0)
+                    HGOTO_ERROR(H5E_DATASPACE, H5E_CANTAPPEND, FAIL, "can't allocate hyperslab span")
+                udata->nelem -= udata->ds_span[udata->depth]->high - udata->ds_low[udata->depth] + 1;
+
+                /* Advance to next span */
+                udata->ds_span[udata->depth] = udata->ds_span[udata->depth]->next;
+                HDassert(udata->ds_span[udata->depth]);
+                udata->ds_low[udata->depth] = udata->ds_span[udata->depth]->low;
+            } while(udata->nelem > 0);
+        } /* end else */
     } /* end while */
 
-    /* Adjust the number of blocks & elements left to transfer */
-
-    /* Decrement number of elements left */
-    H5_CHECK_OVERFLOW(actual_elem * (total_rows * tdiminfo[fast_dim].count), hsize_t, size_t);
-    io_left -= (size_t)(actual_elem * (total_rows * tdiminfo[fast_dim].count));
-
-    /* Decrement number of blocks left */
-    H5_CHECK_OVERFLOW((total_rows * tdiminfo[fast_dim].count), hsize_t, size_t);
-    tot_blk_count -= (size_t)(total_rows * tdiminfo[fast_dim].count);
-
-    /* Read in partial row of blocks */
-    if(io_left > 0 && curr_seq < maxseq) {
-        /* Get remaining number of blocks left to output */
-        fast_dim_count = tot_blk_count;
-
-        /* Loop over all the blocks in the fastest changing dimension */
-        while(fast_dim_count > 0) {
-            /* Store the sequence information */
-            off[curr_seq] = loc;
-            len[curr_seq] = actual_bytes;
-
-            /* Increment sequence count */
-            curr_seq++;
-
-            /* Increment information to reflect block just processed */
-            loc += fast_dim_buf_off;
+    HDassert(udata->skip == 0);
+    HDassert(udata->nelem == 0);
 
-            /* Decrement number of blocks */
-            fast_dim_count--;
-        } /* end while */
+    /* Mark projected space as changed (for all ranks) */
+    udata->ps_clean_bitmap = 0;
 
-        /* Decrement number of elements left */
-        io_left -= actual_elem * tot_blk_count;
-
-        /* Increment information to reflect block just processed */
-        offset[fast_dim] += (fast_dim_stride * tot_blk_count);    /* move the offset in the fastest dimension */
-
-        /* Handle any leftover, partial blocks in this row */
-        if(io_left > 0 && curr_seq < maxseq) {
-            actual_elem = io_left;
-            actual_bytes = actual_elem * elem_size;
-
-            /* Store the sequence information */
-            off[curr_seq] = loc;
-            len[curr_seq] = actual_bytes;
-
-            /* Increment sequence count */
-            curr_seq++;
-
-            /* Decrement the number of elements left */
-            io_left -= actual_elem;
-
-            /* Increment buffer correctly */
-            offset[fast_dim] += actual_elem;
-        } /* end if */
-
-        /* don't bother checking slower dimensions */
-        HDassert(io_left == 0 || curr_seq == maxseq);
+done:
+    /* Cleanup on failure */
+    if(copied_span_info) {
+        HDassert(ret_value < 0);
+        H5S__hyper_free_span_info(copied_span_info);
+        copied_span_info = NULL;
     } /* end if */
 
-    /* Update the iterator */
-
-    /* Update the iterator with the location we stopped */
-    /* (Subtract out the selection offset) */
-    for(u = 0; u < ndims; u++)
-        iter->u.hyp.off[u] = (hsize_t)((hssize_t)offset[u] - sel_off[u]);
-
-    /* Decrement the number of elements left in selection */
-    iter->elmt_left -= (start_io_left - io_left);
-
-    /* Increment the number of sequences generated */
-    *nseq += curr_seq;
-
-    /* Increment the number of elements used */
-    *nelem += start_io_left - io_left;
-
-    FUNC_LEAVE_NOAPI(SUCCEED)
-} /* end H5S__hyper_get_seq_list_opt() */
+    FUNC_LEAVE_NOAPI(ret_value)
+} /* end H5S__hyper_proj_int_build_proj() */
 
 
 /*--------------------------------------------------------------------------
  NAME
-    H5S__hyper_get_seq_list_single
+    H5S__hyper_proj_int_iterate
  PURPOSE
-    Create a list of offsets & lengths for a selection
+    Main iteration routine for H5S__hyper_project_intersection
  USAGE
-    herr_t H5S__hyper_get_seq_list_single(space, flags, iter, maxseq, maxelem, nseq, nelem, off, len)
-        H5S_t *space;           IN: Dataspace containing selection to use.
-        unsigned flags;         IN: Flags for extra information about operation
-        H5S_sel_iter_t *iter;   IN/OUT: Selection iterator describing last
-                                    position of interest in selection.
-        size_t maxseq;          IN: Maximum number of sequences to generate
-        size_t maxelem;         IN: Maximum number of elements to include in the
-                                    generated sequences
-        size_t *nseq;           OUT: Actual number of sequences generated
-        size_t *nelem;          OUT: Actual number of elements in sequences generated
-        hsize_t *off;           OUT: Array of offsets
-        size_t *len;            OUT: Array of lengths
+    herr_t H5S__hyper_proj_int_iterate(ss_span_info,sis_span_info,count,depth,udata)
+        const H5S_hyper_span_info_t *ss_span_info; IN: Span tree for source selection
+        const H5S_hyper_span_info_t *sis_span_info; IN: Span tree for source intersect selection
+        hsize_t count;          IN: Number of times to compute the intersection of ss_span_info and sis_span_info
+        unsigned depth;         IN: Depth of iteration (in terms of rank)
+        H5S_hyper_project_intersect_ud_t *udata; IN/OUT: Persistent shared data for iteration
  RETURNS
     Non-negative on success/Negative on failure.
  DESCRIPTION
-    Use the selection in the dataspace to generate a list of byte offsets and
-    lengths for the region(s) selected.  Start/Restart from the position in the
-    ITER parameter.  The number of sequences generated is limited by the MAXSEQ
-    parameter and the number of sequences actually generated is stored in the
-    NSEQ parameter.
+    Computes the intersection of ss_span_info and sis_span_info and projects it
+    to the projected space (held in udata).  It accomplishes this by iterating
+    over both spaces and computing the number of elements to skip (in
+    ss_span_info) and the number of elements to add (the intersection) in a
+    sequential fashion (similar to run length encoding).  As necessary, this
+    function both recurses into lower dimensions and calls
+    H5S__hyper_proj_int_build_proj to convert the skip/nelem pairs to the
+    projected span tree.
  GLOBAL VARIABLES
  COMMENTS, BUGS, ASSUMPTIONS
  EXAMPLES
  REVISION LOG
 --------------------------------------------------------------------------*/
 static herr_t
-H5S__hyper_get_seq_list_single(const H5S_t *space, H5S_sel_iter_t *iter,
-    size_t maxseq, size_t maxelem, size_t *nseq, size_t *nelem,
-    hsize_t *off, size_t *len)
+H5S__hyper_proj_int_iterate(const H5S_hyper_span_info_t *ss_span_info,
+    const H5S_hyper_span_info_t *sis_span_info, hsize_t count, unsigned depth,
+    H5S_hyper_project_intersect_ud_t *udata)
 {
-    const H5S_hyper_dim_t *tdiminfo;    /* Temporary pointer to diminfo information */
-    const hssize_t *sel_off;    /* Selection offset in dataspace */
-    hsize_t *mem_size;      /* Size of the source buffer */
-    hsize_t base_offset[H5S_MAX_RANK];   /* Base coordinate offset in dataspace */
-    hsize_t offset[H5S_MAX_RANK];   /* Coordinate offset in dataspace */
-    hsize_t slab[H5S_MAX_RANK];     /* Hyperslab size */
-    hsize_t fast_dim_block;     /* Local copies of fastest changing dimension info */
-    hsize_t acc;	        /* Accumulator */
-    hsize_t loc;                /* Coordinate offset */
-    size_t tot_blk_count;       /* Total number of blocks left to output */
-    size_t elem_size;           /* Size of each element iterating over */
-    size_t io_left;             /* The number of elements left in I/O operation */
-    size_t actual_elem;         /* The actual number of elements to count */
-    unsigned ndims;             /* Number of dimensions of dataset */
-    unsigned fast_dim;          /* Rank of the fastest changing dimension for the dataspace */
-    unsigned skip_dim;          /* Rank of the dimension to skip along */
+    const H5S_hyper_span_t *ss_span; /* Current span in source space */
+    const H5S_hyper_span_t *sis_span; /* Current span in source intersect space */
+    hsize_t ss_low;             /* Current low bounds of source span */
+    hsize_t sis_low;            /* Current low bounds of source intersect span */
+    hsize_t high;               /* High bounds of current intersection */
+    hsize_t low;                /* Low bounds of current intersection */
+    hsize_t old_skip;           /* Value of udata->skip before main loop */
+    hsize_t old_nelem;          /* Value of udata->nelem before main loop */
+    hbool_t check_intersect;    /* Whether to check for intersecting elements */
     unsigned u;                 /* Local index variable */
-    int i;                      /* Local index variable */
-
-    FUNC_ENTER_STATIC_NOERR
-
-    /* Check args */
-    HDassert(space);
-    HDassert(iter);
-    HDassert(maxseq > 0);
-    HDassert(maxelem > 0);
-    HDassert(nseq);
-    HDassert(nelem);
-    HDassert(off);
-    HDassert(len);
-
-    /* Set a local copy of the diminfo pointer */
-    tdiminfo = iter->u.hyp.diminfo;
-
-    /* Check if this is a "flattened" regular hyperslab selection */
-    if(iter->u.hyp.iter_rank != 0 && iter->u.hyp.iter_rank < space->extent.rank) {
-        /* Set the aliases for a few important dimension ranks */
-        ndims = iter->u.hyp.iter_rank;
-
-        /* Set the local copy of the selection offset */
-        sel_off = iter->u.hyp.sel_off;
-
-        /* Set up the pointer to the size of the memory space */
-        mem_size = iter->u.hyp.size;
-    } /* end if */
-    else {
-        /* Set the aliases for a few important dimension ranks */
-        ndims = space->extent.rank;
-
-        /* Set the local copy of the selection offset */
-        sel_off = space->select.offset;
-
-        /* Set up the pointer to the size of the memory space */
-        mem_size = space->extent.size;
-    } /* end else */
-    fast_dim = ndims - 1;
-
-    /* initialize row sizes for each dimension */
-    elem_size = iter->elmt_size;
-    for(i = (int)fast_dim, acc = elem_size; i >= 0; i--) {
-        slab[i] = acc;
-        acc *= mem_size[i];
-    } /* end for */
-
-    /* Copy the base location of the block */
-    /* (Add in the selection offset) */
-    for(u = 0; u < ndims; u++)
-        base_offset[u] = (hsize_t)((hssize_t)tdiminfo[u].start + sel_off[u]);
-
-    /* Copy the location of the point to get */
-    /* (Add in the selection offset) */
-    for(u = 0; u < ndims; u++)
-        offset[u] = (hsize_t)((hssize_t)iter->u.hyp.off[u] + sel_off[u]);
-
-    /* Compute the initial buffer offset */
-    for(u = 0, loc = 0; u < ndims; u++)
-        loc += offset[u] * slab[u];
-
-    /* Set local copies of information for the fastest changing dimension */
-    fast_dim_block = tdiminfo[fast_dim].block;
-
-    /* Calculate the number of elements to sequence through */
-    H5_CHECK_OVERFLOW(iter->elmt_left, hsize_t, size_t);
-    io_left = MIN((size_t)iter->elmt_left, maxelem);
-
-    /* Compute the number of blocks which would fit into the buffer */
-    H5_CHECK_OVERFLOW(io_left / fast_dim_block, hsize_t, size_t);
-    tot_blk_count = (size_t)(io_left / fast_dim_block);
-
-    /* Don't go over the maximum number of sequences allowed */
-    tot_blk_count = MIN(tot_blk_count, maxseq);
-
-    /* Set the number of elements to write each time */
-    H5_CHECKED_ASSIGN(actual_elem, size_t, fast_dim_block, hsize_t);
-
-    /* Check for blocks to operate on */
-    if(tot_blk_count > 0) {
-        size_t actual_bytes;        /* The actual number of bytes to copy */
-
-        /* Set the number of actual bytes */
-        actual_bytes = actual_elem * elem_size;
+    herr_t ret_value = SUCCEED; /* Return value */
 
-        /* Check for 1-dim selection */
-        if(0 == fast_dim) {
-            /* Sanity checks */
-            HDassert(1 == tot_blk_count);
-            HDassert(io_left == actual_elem);
+    FUNC_ENTER_STATIC
 
-            /* Store the sequence information */
-            *off++ = loc;
-            *len++ = actual_bytes;
+    /* Check for non-overlapping bounds */
+    check_intersect = TRUE;
+    for(u = 0; u < (udata->ss_rank - depth); u++)
+        if(!H5S_RANGE_OVERLAP(ss_span_info->low_bounds[u],
+                ss_span_info->high_bounds[u],
+                sis_span_info->low_bounds[u],
+                sis_span_info->high_bounds[u])) {
+            check_intersect = FALSE;
+            break;
         } /* end if */
-        else {
-            hsize_t skip_slab;          /* Temporary copy of slab[fast_dim - 1] */
-            size_t blk_count;           /* Total number of blocks left to output */
-
-            /* Find first dimension w/block >1 */
-            skip_dim = fast_dim;
-            for(i = (int)(fast_dim - 1); i >= 0; i--)
-                if(tdiminfo[i].block > 1) {
-                    skip_dim = (unsigned)i;
-                    break;
-                } /* end if */
-            skip_slab = slab[skip_dim];
-
-            /* Check for being able to use fast algorithm for 1-D */
-            if(0 == skip_dim) {
-                /* Create sequences until an entire row can't be used */
-                blk_count = tot_blk_count;
-                while(blk_count > 0) {
-                    /* Store the sequence information */
-                    *off++ = loc;
-                    *len++ = actual_bytes;
 
-                    /* Increment offset in destination buffer */
-                    loc += skip_slab;
+    /* Only enter main loop if there's something to do */
+    if(check_intersect) {
+        /* Set ps_clean_bitmap */
+        udata->ps_clean_bitmap |= (((uint32_t)1) << depth);
 
-                    /* Decrement block count */
-                    blk_count--;
-                } /* end while */
-
-                /* Move to the next location */
-                offset[skip_dim] += tot_blk_count;
-            } /* end if */
-            else {
-                hsize_t tmp_block[H5S_MAX_RANK];/* Temporary block offset */
-                hsize_t skip[H5S_MAX_RANK];     /* Bytes to skip between blocks */
-                int temp_dim;               /* Temporary rank holder */
+        /* Save old skip and nelem */
+        old_skip = udata->skip;
+        old_nelem = udata->nelem;
 
-                /* Set the starting block location */
-                for(u = 0; u < ndims; u++)
-                    tmp_block[u] = iter->u.hyp.off[u] - tdiminfo[u].start;
+        /* Intersect spaces once per count */
+        for(u = 0; u < count; u++) {
+            ss_span = ss_span_info->head;
+            sis_span = sis_span_info->head;
+            HDassert(ss_span && sis_span);
+            ss_low = ss_span->low;
+            sis_low = sis_span->low;
 
-                /* Compute the amount to skip between sequences */
-                for(u = 0; u < ndims; u++)
-                    skip[u] = (mem_size[u] - tdiminfo[u].block) * slab[u];
-
-                /* Create sequences until an entire row can't be used */
-                blk_count = tot_blk_count;
-                while(blk_count > 0) {
-                    /* Store the sequence information */
-                    *off++ = loc;
-                    *len++ = actual_bytes;
+            /* Main loop */
+            do {
+                /* Check if spans overlap */
+                if(H5S_RANGE_OVERLAP(ss_low, ss_span->high,
+                        sis_low, sis_span->high)) {
+                    high = MIN(ss_span->high, sis_span->high);
+                    if(ss_span->down) {
+                        /* Add skipped elements if there's a pre-gap */
+                        if(ss_low < sis_low) {
+                            low = sis_low;
+                            H5S_HYPER_PROJ_INT_ADD_SKIP(udata, H5S__hyper_spans_nelem_helper(ss_span->down, 0, udata->op_gen) * (sis_low - ss_low), FAIL);
+                        } /* end if */
+                        else
+                            low = ss_low;
 
-                    /* Set temporary dimension for advancing offsets */
-                    temp_dim = (int)skip_dim;
+                        /* Recurse into next dimension down */
+                        if(H5S__hyper_proj_int_iterate(ss_span->down, sis_span->down, high - low + 1, depth + 1, udata) < 0)
+                            HGOTO_ERROR(H5E_DATASPACE, H5E_CANTCOMPARE, FAIL, "can't iterate over source selections")
+                    } /* end if */
+                    else {
+                        HDassert(depth == udata->ss_rank - 1);
 
-                    /* Increment offset in destination buffer */
-                    loc += skip_slab;
+                        /* Add skipped elements if there's a pre-gap */
+                        if(ss_low < sis_low) {
+                            low = sis_low;
+                            H5S_HYPER_PROJ_INT_ADD_SKIP(udata, sis_low - ss_low, FAIL);
+                        } /* end if */
+                        else
+                            low = ss_low;
 
-                    /* Increment the offset and count for the other dimensions */
-                    while(temp_dim >= 0) {
-                        /* Move to the next row in the curent dimension */
-                        offset[temp_dim]++;
-                        tmp_block[temp_dim]++;
+                        /* Add overlapping elements */
+                        udata->nelem += high - low + 1;
+                    } /* end else */
 
-                        /* If this block is still in the range of blocks to output for the dimension, break out of loop */
-                        if(tmp_block[temp_dim] < tdiminfo[temp_dim].block)
-                            break;
-                        else {
-                            offset[temp_dim] = base_offset[temp_dim];
-                            loc += skip[temp_dim];
-                            tmp_block[temp_dim] = 0;
-                        } /* end else */
+                    /* Advance spans */
+                    if(ss_span->high == sis_span->high) {
+                        /* Advance both spans */
+                        ss_span = ss_span->next;
+                        if(ss_span)
+                            ss_low = ss_span->low;
+                        sis_span = sis_span->next;
+                        if(sis_span)
+                            sis_low = sis_span->low;
+                    } /* end if */
+                    else if(ss_span->high == high) {
+                        /* Advance source span */
+                        HDassert(ss_span->high < sis_span->high);
+                        sis_low = high + 1;
+                        ss_span = ss_span->next;
+                        if(ss_span)
+                            ss_low = ss_span->low;
+                    } /* end if */
+                    else {
+                        /* Advance source intersect span */
+                        HDassert(ss_span->high > sis_span->high);
+                        ss_low = high + 1;
+                        sis_span = sis_span->next;
+                        if(sis_span)
+                            sis_low = sis_span->low;
+                    } /* end else */
+                } /* end if */
+                else {
+                    /* Advance spans */
+                    if(ss_span->high < sis_low) {
+                        /* Add skipped elements */
+                        if(ss_span->down)
+                            H5S_HYPER_PROJ_INT_ADD_SKIP(udata, H5S__hyper_spans_nelem_helper(ss_span->down, 0, udata->op_gen) * (ss_span->high - ss_low + 1), FAIL);
+                        else
+                            H5S_HYPER_PROJ_INT_ADD_SKIP(udata, ss_span->high - ss_low + 1, FAIL);
 
-                        /* Decrement dimension count */
-                        temp_dim--;
+                        /* Advance source span */
+                        ss_span = ss_span->next;
+                        if(ss_span)
+                            ss_low = ss_span->low;
+                    } /* end if */
+                    else {
+                        /* Advance source intersect span */
+                        HDassert(ss_low > sis_span->high);
+                        sis_span = sis_span->next;
+                        if(sis_span)
+                            sis_low = sis_span->low;
+                    } /* end else */
+                } /* end else */
+            } while(ss_span && sis_span);
+
+            if(ss_span && !((depth == 0) && (u == count - 1))) {
+                /* Count remaining elements in ss_span_info */
+                if(ss_span->down) {
+                    H5S_HYPER_PROJ_INT_ADD_SKIP(udata, H5S__hyper_spans_nelem_helper(ss_span->down, 0, udata->op_gen) * (ss_span->high - ss_low + 1), FAIL);
+                    ss_span = ss_span->next;
+                    while(ss_span) {
+                        H5S_HYPER_PROJ_INT_ADD_SKIP(udata, H5S__hyper_spans_nelem_helper(ss_span->down, 0, udata->op_gen) * (ss_span->high - ss_span->low + 1), FAIL);
+                        ss_span = ss_span->next;
                     } /* end while */
-
-                    /* Decrement block count */
-                    blk_count--;
-                } /* end while */
-            } /* end else */
-        } /* end else */
-
-        /* Update the iterator, if there were any blocks used */
-
-        /* Decrement the number of elements left in selection */
-        iter->elmt_left -= tot_blk_count * actual_elem;
-
-        /* Check if there are elements left in iterator */
-        if(iter->elmt_left > 0) {
-            /* Update the iterator with the location we stopped */
-            /* (Subtract out the selection offset) */
-            for(u = 0; u < ndims; u++)
-                iter->u.hyp.off[u] = (hsize_t)((hssize_t)offset[u] - sel_off[u]);
-        } /* end if */
-
-        /* Increment the number of sequences generated */
-        *nseq += tot_blk_count;
-
-        /* Increment the number of elements used */
-        *nelem += tot_blk_count * actual_elem;
-    } /* end if */
-
-    /* Check for partial block, with room for another sequence */
-    if(io_left > (tot_blk_count * actual_elem) && tot_blk_count < maxseq) {
-        size_t elmt_remainder;  /* Elements remaining */
-
-        /* Compute elements left */
-        elmt_remainder = io_left - (tot_blk_count * actual_elem);
-        HDassert(elmt_remainder < fast_dim_block);
-        HDassert(elmt_remainder > 0);
-
-        /* Store the sequence information */
-        *off++ = loc;
-        *len++ = elmt_remainder * elem_size;
-
-        /* Update the iterator with the location we stopped */
-        iter->u.hyp.off[fast_dim] += (hsize_t)elmt_remainder;
-
-        /* Decrement the number of elements left in selection */
-        iter->elmt_left -= elmt_remainder;
-
-        /* Increment the number of sequences generated */
-        (*nseq)++;
-
-        /* Increment the number of elements used */
-        *nelem += elmt_remainder;
-    } /* end if */
-
-    /* Sanity check */
-    HDassert(*nseq > 0);
-    HDassert(*nelem > 0);
-
-    FUNC_LEAVE_NOAPI(SUCCEED)
-} /* end H5S__hyper_get_seq_list_single() */
-
-
-/*--------------------------------------------------------------------------
- NAME
-    H5S__hyper_get_seq_list
- PURPOSE
-    Create a list of offsets & lengths for a selection
- USAGE
-    herr_t H5S__hyper_get_seq_list(space,flags,iter,maxseq,maxelem,nseq,nelem,off,len)
-        H5S_t *space;           IN: Dataspace containing selection to use.
-        unsigned flags;         IN: Flags for extra information about operation
-        H5S_sel_iter_t *iter;   IN/OUT: Selection iterator describing last
-                                    position of interest in selection.
-        size_t maxseq;          IN: Maximum number of sequences to generate
-        size_t maxelem;         IN: Maximum number of elements to include in the
-                                    generated sequences
-        size_t *nseq;           OUT: Actual number of sequences generated
-        size_t *nelem;          OUT: Actual number of elements in sequences generated
-        hsize_t *off;           OUT: Array of offsets
-        size_t *len;            OUT: Array of lengths
- RETURNS
-    Non-negative on success/Negative on failure.
- DESCRIPTION
-    Use the selection in the dataspace to generate a list of byte offsets and
-    lengths for the region(s) selected.  Start/Restart from the position in the
-    ITER parameter.  The number of sequences generated is limited by the MAXSEQ
-    parameter and the number of sequences actually generated is stored in the
-    NSEQ parameter.
- GLOBAL VARIABLES
- COMMENTS, BUGS, ASSUMPTIONS
- EXAMPLES
- REVISION LOG
---------------------------------------------------------------------------*/
-static herr_t
-H5S__hyper_get_seq_list(const H5S_t *space, unsigned H5_ATTR_UNUSED flags, H5S_sel_iter_t *iter,
-    size_t maxseq, size_t maxelem, size_t *nseq, size_t *nelem,
-    hsize_t *off, size_t *len)
-{
-    herr_t ret_value = FAIL;    /* return value */
-
-    FUNC_ENTER_STATIC_NOERR
-
-    /* Check args */
-    HDassert(space);
-    HDassert(iter);
-    HDassert(iter->elmt_left > 0);
-    HDassert(maxseq > 0);
-    HDassert(maxelem > 0);
-    HDassert(nseq);
-    HDassert(nelem);
-    HDassert(off);
-    HDassert(len);
-    HDassert(space->select.sel_info.hslab->unlim_dim < 0);
-
-    /* Check for the special case of just one H5Sselect_hyperslab call made */
-    if(H5S_DIMINFO_VALID_YES == space->select.sel_info.hslab->diminfo_valid) {
-        const H5S_hyper_dim_t *tdiminfo;    /* Temporary pointer to diminfo information */
-        const hssize_t *sel_off;    /* Selection offset in dataspace */
-        hsize_t *mem_size;      /* Size of the source buffer */
-        unsigned ndims;         /* Number of dimensions of dataset */
-        unsigned fast_dim;      /* Rank of the fastest changing dimension for the dataspace */
-        hbool_t single_block;   /* Whether the selection is a single block */
-        unsigned u;             /* Local index variable */
-
-        /* Set a local copy of the diminfo pointer */
-        tdiminfo = iter->u.hyp.diminfo;
-
-        /* Check if this is a "flattened" regular hyperslab selection */
-        if(iter->u.hyp.iter_rank != 0 && iter->u.hyp.iter_rank < space->extent.rank) {
-            /* Set the aliases for a few important dimension ranks */
-            ndims = iter->u.hyp.iter_rank;
-
-            /* Set the local copy of the selection offset */
-            sel_off = iter->u.hyp.sel_off;
-
-            /* Set up the pointer to the size of the memory space */
-            mem_size = iter->u.hyp.size;
-        } /* end if */
-        else {
-            /* Set the aliases for a few important dimension ranks */
-            ndims = space->extent.rank;
-
-            /* Set the local copy of the selection offset */
-            sel_off = space->select.offset;
-
-            /* Set up the pointer to the size of the memory space */
-            mem_size = space->extent.size;
-        } /* end else */
-        fast_dim = ndims - 1;
-
-        /* Check if we stopped in the middle of a sequence of elements */
-        if((iter->u.hyp.off[fast_dim] - tdiminfo[fast_dim].start) % tdiminfo[fast_dim].stride != 0 ||
-                ((iter->u.hyp.off[fast_dim] != tdiminfo[fast_dim].start) && tdiminfo[fast_dim].count == 1)) {
-            hsize_t slab[H5S_MAX_RANK];     /* Hyperslab size */
-            hsize_t loc;                /* Coordinate offset */
-            hsize_t acc;	        /* Accumulator */
-            size_t leftover;            /* The number of elements left over from the last sequence */
-            size_t actual_elem;         /* The actual number of elements to count */
-            size_t elem_size;           /* Size of each element iterating over */
-            int i;                      /* Local index variable */
-
-
-            /* Calculate the number of elements left in the sequence */
-            if(tdiminfo[fast_dim].count == 1) {
-                H5_CHECKED_ASSIGN(leftover, size_t, tdiminfo[fast_dim].block - (iter->u.hyp.off[fast_dim] - tdiminfo[fast_dim].start), hsize_t);
+                } /* end if */
+                else {
+                    H5S_HYPER_PROJ_INT_ADD_SKIP(udata, ss_span->high - ss_low + 1, FAIL);
+                    ss_span = ss_span->next;
+                    while(ss_span) {
+                        H5S_HYPER_PROJ_INT_ADD_SKIP(udata, ss_span->high - ss_span->low + 1, FAIL);
+                        ss_span = ss_span->next;
+                    } /* end while */
+                } /* end else */
             } /* end if */
-            else {
-                H5_CHECKED_ASSIGN(leftover, size_t, tdiminfo[fast_dim].block - ((iter->u.hyp.off[fast_dim] - tdiminfo[fast_dim].start) % tdiminfo[fast_dim].stride), hsize_t);
-            } /* end else */
-
-            /* Make certain that we don't write too many */
-            actual_elem = MIN3(leftover, (size_t)iter->elmt_left, maxelem);
-
-            /* Initialize row sizes for each dimension */
-            elem_size = iter->elmt_size;
-            for(i = (int)fast_dim, acc = elem_size; i >= 0; i--) {
-                slab[i] = acc;
-                acc *= mem_size[i];
-            } /* end for */
-
-            /* Compute the initial buffer offset */
-            for(u = 0, loc = 0; u < ndims; u++)
-                loc += ((hsize_t)((hssize_t)iter->u.hyp.off[u] + sel_off[u])) * slab[u];
-
-            /* Add a new sequence */
-            off[0] = loc;
-            H5_CHECKED_ASSIGN(len[0], size_t, actual_elem * elem_size, hsize_t);
-
-            /* Increment sequence array locations */
-            off++;
-            len++;
-
-            /* Advance the hyperslab iterator */
-            H5S__hyper_iter_next(iter, actual_elem);
 
-            /* Decrement the number of elements left in selection */
-            iter->elmt_left -= actual_elem;
-
-            /* Decrement element/sequence limits */
-            maxelem -= actual_elem;
-            maxseq--;
-
-            /* Set the number of sequences generated and elements used */
-            *nseq = 1;
-            *nelem = actual_elem;
-
-            /* Check for using up all the sequences/elements */
-            if(0 == iter->elmt_left || 0 == maxelem || 0 == maxseq)
-                return(SUCCEED);
-        } /* end if */
-        else {
-            /* Reset the number of sequences generated and elements used */
-            *nseq = 0;
-            *nelem = 0;
-        } /* end else */
+            /* Check if the projected space was not changed since we started the
+             * first iteration of the loop, if so we do not need to continue
+             * looping and can just copy the result */
+            if(udata->ps_clean_bitmap & (((uint32_t)1) << depth)) {
+                HDassert(u == 0);
+                if(udata->skip == old_skip) {
+                    /* First case: algorithm added only elements */
+                    HDassert(udata->nelem >= old_nelem);
+                    udata->nelem += (count - 1) * (udata->nelem - old_nelem);
+                } /* end if */
+                else if(udata->nelem == 0) {
+                    /* Second case: algorithm added only skip.  In this case,
+                     * nelem must be 0 since otherwise adding skip would have
+                     * triggered a change in the projected space */
+                    HDassert(old_nelem == 0);
+                    HDassert(udata->skip > old_skip);
+                    udata->skip += (count - 1) * (udata->skip - old_skip);
+                } /* end if */
+                else {
+                    /* Third case: agorithm added skip and nelem (in that
+                     * order).  Add the same skip and nelem once for each item
+                     * remaining in count. */
+                    hsize_t skip_add;
+                    hsize_t nelem_add;
+
+                    HDassert(udata->nelem > 0);
+                    HDassert(udata->skip > old_skip);
+                    HDassert(old_nelem == 0);
+
+                    skip_add = udata->skip - old_skip;
+                    nelem_add = udata->nelem - old_nelem;
+                    for(u = 1; u < count; u++) {
+                        H5S_HYPER_PROJ_INT_ADD_SKIP(udata, skip_add, FAIL);
+                        udata->nelem += nelem_add;
+                    } /* end for */
+                } /* end else */
 
-        /* Check for a single block selected */
-        single_block = TRUE;
-        for(u = 0; u < ndims; u++)
-            if(1 != tdiminfo[u].count) {
-                single_block = FALSE;
+                /* End loop since we already took care of it */
                 break;
             } /* end if */
-
-        /* Check for single block selection */
-        if(single_block)
-            /* Use single-block optimized call to generate sequence list */
-            ret_value = H5S__hyper_get_seq_list_single(space, iter, maxseq, maxelem, nseq, nelem, off, len);
-        else
-            /* Use optimized call to generate sequence list */
-            ret_value = H5S__hyper_get_seq_list_opt(space, iter, maxseq, maxelem, nseq, nelem, off, len);
+        } /* end for */
+    } /* end if */
+    else if(depth > 0)
+        /* Just count skipped elements */
+        H5S_HYPER_PROJ_INT_ADD_SKIP(udata, H5S__hyper_spans_nelem_helper((H5S_hyper_span_info_t *)ss_span_info, 0, udata->op_gen) * count, FAIL); /* Casting away const OK -NAF */
+
+    /* Clean up if we are done */
+    if(depth == 0) {
+        /* Add remaining elements */
+        if(udata->nelem > 0)
+            if(H5S__hyper_proj_int_build_proj(udata) < 0)
+                HGOTO_ERROR(H5E_DATASPACE, H5E_CANTAPPEND, FAIL, "can't add elements to projected selection")
+
+        /* Append remaining span trees */
+        for(u = udata->ds_rank - 1; u > 0; u--)
+            if(udata->ps_span_info[u]) {
+                if(H5S__hyper_append_span(&udata->ps_span_info[u - 1],
+                        udata->ds_rank - u + 1, udata->ds_low[u - 1],
+                        udata->ds_low[u - 1],
+                        udata->ps_span_info[u]) < 0)
+                    HGOTO_ERROR(H5E_DATASPACE, H5E_CANTAPPEND, FAIL, "can't allocate hyperslab span")
+                H5S__hyper_free_span_info(udata->ps_span_info[u]);
+                udata->ps_span_info[u] = NULL;
+            } /* end if */
     } /* end if */
-    else
-        /* Call the general sequence generator routine */
-        ret_value = H5S__hyper_get_seq_list_gen(space, iter, maxseq, maxelem, nseq, nelem, off, len);
 
+done:
     FUNC_LEAVE_NOAPI(ret_value)
-} /* end H5S__hyper_get_seq_list() */
+} /* end H5S__hyper_proj_int_iterate() */
 
 
 /*--------------------------------------------------------------------------
@@ -9320,21 +11281,23 @@ H5S__hyper_get_seq_list(const H5S_t *space, unsigned H5_ATTR_UNUSED flags, H5S_s
     src_intersect_space within the selection of src_space as a selection
     within the selection of dst_space
  USAGE
-    herr_t H5S__hyper_project_intersection(src_space,dst_space,src_intersect_space,proj_space)
+    herr_t H5S__hyper_project_intersection(src_space,dst_space,src_intersect_space,proj_space,share_selection)
         H5S_t *src_space;       IN: Selection that is mapped to dst_space, and intersected with src_intersect_space
         H5S_t *dst_space;       IN: Selection that is mapped to src_space, and which contains the result
         H5S_t *src_intersect_space; IN: Selection whose intersection with src_space is projected to dst_space to obtain the result
         H5S_t *proj_space;      OUT: Will contain the result (intersection of src_intersect_space and src_space projected from src_space to dst_space) after the operation
+        hbool_t share_selection; IN: Whether we are allowed to share structures inside dst_space with proj_space
  RETURNS
     Non-negative on success/Negative on failure.
  DESCRIPTION
     Projects the intersection of of the selections of src_space and
     src_intersect_space within the selection of src_space as a selection
-    within the selection of dst_space.  The result is placed in the
-    selection of proj_space.  Note src_space, dst_space, and
-    src_intersect_space do not need to use hyperslab selections, but they
-    cannot use point selections.  The result is always a hyperslab
-    selection.
+    within the selection of dst_space.  The result is placed in the selection
+    of proj_space.  Note src_space, dst_space, and src_intersect_space do not
+    need to use hyperslab selections, but they cannot use point selections.
+    The result is always a hyperslab or none selection.  Note also that
+    proj_space can share some span trees with dst_space, so proj_space
+    must not be subsequently modified if dst_space must be preserved.
  GLOBAL VARIABLES
  COMMENTS, BUGS, ASSUMPTIONS
  EXAMPLES
@@ -9342,48 +11305,14 @@ H5S__hyper_get_seq_list(const H5S_t *space, unsigned H5_ATTR_UNUSED flags, H5S_s
 --------------------------------------------------------------------------*/
 herr_t
 H5S__hyper_project_intersection(const H5S_t *src_space, const H5S_t *dst_space,
-    const H5S_t *src_intersect_space, H5S_t *proj_space)
+    const H5S_t *src_intersect_space, H5S_t *proj_space,
+    hbool_t share_selection)
 {
-    hsize_t             ss_off[H5S_PROJECT_INTERSECT_NSEQS]; /* Offset array for src_space */
-    size_t              ss_len[H5S_PROJECT_INTERSECT_NSEQS]; /* Length array for src_space */
-    size_t              ss_nseq;        /* Number of sequences for src_space */
-    size_t              ss_nelem;       /* Number of elements for src_space */
-    size_t              ss_i = (size_t)0; /* Index into offset/length arrays for src_space */
-    hbool_t             advance_ss = FALSE; /* Whether to advance ss_i on the next iteration */
-    H5S_sel_iter_t      *ss_iter = NULL; /* Selection iterator for src_space */
-    hbool_t             ss_iter_init = FALSE; /* Whether ss_iter is initialized */
-    hsize_t             ss_sel_off = (hsize_t)0; /* Offset within src_space selection */
-    hsize_t             ds_off[H5S_PROJECT_INTERSECT_NSEQS]; /* Offset array for dst_space */
-    size_t              ds_len[H5S_PROJECT_INTERSECT_NSEQS]; /* Length array for dst_space */
-    size_t              ds_nseq;        /* Number of sequences for dst_space */
-    size_t              ds_nelem;       /* Number of elements for dst_space */
-    size_t              ds_i = (size_t)0; /* Index into offset/length arrays for dst_space */
-    H5S_sel_iter_t      *ds_iter = NULL; /* Selection iterator for dst_space */
-    hbool_t             ds_iter_init = FALSE; /* Whether ds_iter is initialized */
-    hsize_t             ds_sel_off = (hsize_t)0; /* Offset within dst_space selection */
-    hsize_t             sis_off[H5S_PROJECT_INTERSECT_NSEQS]; /* Offset array for src_intersect_space */
-    size_t              sis_len[H5S_PROJECT_INTERSECT_NSEQS]; /* Length array for src_intersect_space */
-    size_t              sis_nseq;       /* Number of sequences for src_intersect_space */
-    size_t              sis_nelem;      /* Number of elements for src_intersect_space */
-    size_t              sis_i = (size_t)0; /* Index into offset/length arrays for src_intersect_space */
-    hbool_t             advance_sis = FALSE; /* Whether to advance sis_i on the next iteration */
-    H5S_sel_iter_t      *sis_iter = NULL; /* Selection iterator for src_intersect_space */
-    hbool_t             sis_iter_init = FALSE; /* Whether sis_iter is initialized */
-    hsize_t             int_sel_off;    /* Offset within intersected selections (ss/sis and ds/ps) */
-    size_t              int_len;        /* Length of segment in intersected selections */
-    hsize_t             proj_off;       /* Segment offset in proj_space */
-    size_t              proj_len;       /* Segment length in proj_space */
-    size_t              proj_len_rem;   /* Remaining length in proj_space for segment */
-    hsize_t             proj_down_dims[H5S_MAX_RANK]; /* "Down" dimensions in proj_space */
-    H5S_hyper_span_info_t *curr_span_tree[H5S_MAX_RANK]; /* Current span tree being built (in each dimension) */
-    H5S_hyper_span_t    *prev_span[H5S_MAX_RANK]; /* Previous span in tree (in each dimension) */
-    hsize_t             curr_span_up_dim[H5S_MAX_RANK]; /* "Up" dimensions for current span */
-    unsigned            proj_rank;      /* Rank of proj_space */
-    hsize_t             low;            /* Low value of span */
-    hsize_t             high;           /* High value of span */
-    size_t              span_len;       /* Length of span */
-    size_t              nelem;          /* Number of elements returned for get_seq_list op */
-    unsigned            i;              /* Local index variable */
+    H5S_hyper_project_intersect_ud_t  udata; /* User data for subroutines */
+    const H5S_hyper_span_info_t *ss_span_info;
+    const H5S_hyper_span_info_t *ds_span_info;
+    H5S_hyper_span_info_t *ss_span_info_buf = NULL;
+    H5S_hyper_span_info_t *ds_span_info_buf = NULL;
     herr_t              ret_value = SUCCEED; /* Return value */
 
     FUNC_ENTER_PACKAGE
@@ -9394,303 +11323,100 @@ H5S__hyper_project_intersection(const H5S_t *src_space, const H5S_t *dst_space,
     HDassert(src_intersect_space);
     HDassert(proj_space);
 
-    /* Assert that src_space and src_intersect_space have same extent and there
+    /* Assert that src_space and src_intersect_space have same rank and there
      * are no point selections */
-    HDassert(H5S_GET_EXTENT_NDIMS(src_space)
-            == H5S_GET_EXTENT_NDIMS(src_intersect_space));
-    HDassert(!HDmemcmp(src_space->extent.size, src_intersect_space->extent.size,
-            (size_t)H5S_GET_EXTENT_NDIMS(src_space)
-            * sizeof(src_space->extent.size[0])));
+    HDassert(H5S_GET_EXTENT_NDIMS(src_space) == H5S_GET_EXTENT_NDIMS(src_intersect_space));
+    HDassert(H5S_GET_SELECT_NPOINTS(src_space) == H5S_GET_SELECT_NPOINTS(dst_space));
     HDassert(H5S_GET_SELECT_TYPE(src_space) != H5S_SEL_POINTS);
     HDassert(H5S_GET_SELECT_TYPE(dst_space) != H5S_SEL_POINTS);
-    HDassert(H5S_GET_SELECT_TYPE(src_intersect_space) != H5S_SEL_POINTS);
-
-    /* Initialize prev_space, curr_span_tree, and curr_span_up_dim */
-    for(i = 0; i < H5S_MAX_RANK; i++) {
-        curr_span_tree[i] = NULL;
-        prev_span[i] = NULL;
-        curr_span_up_dim[i] = (hsize_t)0;
-    } /* end for */
-
-    /* Save rank of projected space */
-    proj_rank = proj_space->extent.rank;
-    HDassert(proj_rank > 0);
-
-    /* Get numbers of elements */
-    ss_nelem = (size_t)H5S_GET_SELECT_NPOINTS(src_space);
-    ds_nelem = (size_t)H5S_GET_SELECT_NPOINTS(dst_space);
-    sis_nelem = (size_t)H5S_GET_SELECT_NPOINTS(src_intersect_space);
-    HDassert(ss_nelem == ds_nelem);
-
-    /* Calculate proj_down_dims (note loop relies on unsigned i wrapping around)
-     */
-    if(H5VM_array_down(proj_rank, proj_space->extent.size, proj_down_dims) < 0)
-        HGOTO_ERROR(H5E_DATASPACE, H5E_CANTSET, FAIL, "can't compute 'down' chunk size value")
-
-    /* Remove current selection from proj_space */
-    if(H5S_SELECT_RELEASE(proj_space) < 0)
-        HGOTO_ERROR(H5E_DATASPACE, H5E_CANTDELETE, FAIL, "can't release selection")
+    HDassert(H5S_GET_SELECT_TYPE(src_intersect_space) == H5S_SEL_HYPERSLABS);
 
-    /* If any selections are empty, skip to the end so "none" is selected */
-    if((ss_nelem == 0) || (ds_nelem == 0) || (sis_nelem == 0))
-        goto loop_end;
+    /* Set up ss_span_info */
+    if(H5S_GET_SELECT_TYPE(src_space) == H5S_SEL_HYPERSLABS) {
+        /* Make certain the selection has a span tree */
+        if(NULL == src_space->select.sel_info.hslab->span_lst)
+            if(H5S__hyper_generate_spans((H5S_t *)src_space) < 0)  /* Casting away const OK -NAF */
+                HGOTO_ERROR(H5E_DATASPACE, H5E_UNINITIALIZED, FAIL, "can't construct span tree for source hyperslab selection")
 
-    /* Allocate space for the hyperslab selection information (note this sets
-     * diminfo arrays to 0, and span list to NULL)
-     */
-    if((proj_space->select.sel_info.hslab = H5FL_CALLOC(H5S_hyper_sel_t)) == NULL)
-        HGOTO_ERROR(H5E_DATASPACE, H5E_CANTALLOC, FAIL, "can't allocate hyperslab info")
-    proj_space->select.sel_info.hslab->diminfo_valid = H5S_DIMINFO_VALID_NO;
-
-    /* Set selection type */
-    proj_space->select.type = H5S_sel_hyper;
-
-    /* Set unlim_dim */
-    proj_space->select.sel_info.hslab->unlim_dim = -1;
-
-    /* Allocate the source space iterator */
-    if(NULL == (ss_iter = H5FL_MALLOC(H5S_sel_iter_t)))
-        HGOTO_ERROR(H5E_DATASPACE, H5E_CANTALLOC, FAIL, "can't allocate source space iterator")
-
-    /* Initialize source space iterator */
-    if(H5S_select_iter_init(ss_iter, src_space, (size_t)1) < 0)
-        HGOTO_ERROR(H5E_DATASPACE, H5E_CANTINIT, FAIL, "unable to initialize selection iterator")
-    ss_iter_init = TRUE;
-
-    /* Get sequence list for source space */
-    if(H5S_SELECT_GET_SEQ_LIST(src_space, 0u, ss_iter, H5S_PROJECT_INTERSECT_NSEQS, ss_nelem, &ss_nseq, &nelem, ss_off, ss_len) < 0)
-        HGOTO_ERROR(H5E_INTERNAL, H5E_UNSUPPORTED, FAIL, "sequence length generation failed")
-    ss_nelem -= nelem;
-    HDassert(ss_nseq > 0);
-
-    /* Allocate the destination space iterator */
-    if(NULL == (ds_iter = H5FL_MALLOC(H5S_sel_iter_t)))
-        HGOTO_ERROR(H5E_DATASPACE, H5E_CANTALLOC, FAIL, "can't allocate destination space iterator")
-
-    /* Initialize destination space iterator */
-    if(H5S_select_iter_init(ds_iter, dst_space, (size_t)1) < 0)
-        HGOTO_ERROR(H5E_DATASPACE, H5E_CANTINIT, FAIL, "unable to initialize selection iterator")
-    ds_iter_init = TRUE;
-
-    /* Get sequence list for destination space */
-    if(H5S_SELECT_GET_SEQ_LIST(dst_space, 0u, ds_iter, H5S_PROJECT_INTERSECT_NSEQS, ds_nelem, &ds_nseq, &nelem, ds_off, ds_len) < 0)
-        HGOTO_ERROR(H5E_DATASPACE, H5E_CANTINIT, FAIL, "unable to initialize selection iterator")
-    ds_nelem -= nelem;
-    HDassert(ds_nseq > 0);
-
-    /* Allocate the source intersect space iterator */
-    if(NULL == (sis_iter = H5FL_MALLOC(H5S_sel_iter_t)))
-        HGOTO_ERROR(H5E_DATASPACE, H5E_CANTALLOC, FAIL, "can't allocate source intersect space iterator")
-
-    /* Initialize source intersect space iterator */
-    if(H5S_select_iter_init(sis_iter, src_intersect_space, (size_t)1) < 0)
-        HGOTO_ERROR(H5E_DATASPACE, H5E_CANTINIT, FAIL, "unable to initialize selection iterator")
-    sis_iter_init = TRUE;
-
-    /* Get sequence list for source intersect space */
-    if(H5S_SELECT_GET_SEQ_LIST(src_intersect_space, 0u, sis_iter, H5S_PROJECT_INTERSECT_NSEQS, sis_nelem, &sis_nseq, &nelem, sis_off, sis_len) < 0)
-        HGOTO_ERROR(H5E_INTERNAL, H5E_UNSUPPORTED, FAIL, "sequence length generation failed")
-    sis_nelem -= nelem;
-    HDassert(sis_nseq > 0);
-
-    /* Loop until we run out of sequences in either the source or source
-     * intersect space */
-    while(1) {
-        while(advance_ss || (ss_off[ss_i] + ss_len[ss_i] <= sis_off[sis_i])) {
-            /* Either we finished the current source sequence or the
-             * sequences do not intersect.  Advance source space. */
-            ss_sel_off += (hsize_t)ss_len[ss_i];
-            if(++ss_i == ss_nseq) {
-                if(ss_nelem > 0) {
-                    /* Try to grab more sequences from src_space */
-                    if(H5S_SELECT_GET_SEQ_LIST(src_space, 0u, ss_iter, H5S_PROJECT_INTERSECT_NSEQS, ss_nelem, &ss_nseq, &nelem, ss_off, ss_len) < 0)
-                        HGOTO_ERROR(H5E_INTERNAL, H5E_UNSUPPORTED, FAIL, "sequence length generation failed")
-                    HDassert(ss_len[0] > 0);
-
-                    /* Update ss_nelem */
-                    HDassert(nelem > 0);
-                    HDassert(nelem <= ss_nelem);
-                    ss_nelem -= nelem;
-
-                    /* Reset source space index */
-                    ss_i = 0;
-                } /* end if */
-                else
-                    /* There are no more sequences in src_space, so we can exit
-                     * the loop.  Use goto instead of break so we exit the outer
-                     * loop. */
-                    goto loop_end;
-            } /* end if */
-
-            /* Reset advance_ss */
-            advance_ss = FALSE;
-        } /* end if */
-        if(advance_sis
-                || (sis_off[sis_i] + sis_len[sis_i] <= ss_off[ss_i])) {
-            do {
-                /* Either we finished the current source intersect sequence or
-                 * the sequences do not intersect.  Advance source intersect
-                 * space. */
-                if(++sis_i == sis_nseq) {
-                    if(sis_nelem > 0) {
-                        /* Try to grab more sequences from src_intersect_space
-                         */
-                        if(H5S_SELECT_GET_SEQ_LIST(src_intersect_space, 0u, sis_iter, H5S_PROJECT_INTERSECT_NSEQS, sis_nelem, &sis_nseq, &nelem, sis_off, sis_len) < 0)
-                            HGOTO_ERROR(H5E_INTERNAL, H5E_UNSUPPORTED, FAIL, "sequence length generation failed")
-                        HDassert(sis_len[0] > 0);
-
-                        /* Update ss_nelem */
-                        HDassert(nelem > 0);
-                        HDassert(nelem <= sis_nelem);
-                        sis_nelem -= nelem;
-
-                        /* Reset source space index */
-                        sis_i = 0;
-                    } /* end if */
-                    else
-                        /* There are no more sequences in src_intersect_space,
-                         * so we can exit the loop.  Use goto instead of break
-                         * so we exit the outer loop. */
-                        goto loop_end;
-                } /* end if */
-            } while(sis_off[sis_i] + sis_len[sis_i] <= ss_off[ss_i]);
-
-            /* Reset advance_sis */
-            advance_sis = FALSE;
-        } /* end if */
-        else {
-            /* Sequences intersect, add intersection to projected space */
-            /* Calculate intersection sequence in terms of offset within source
-             * selection and advance any sequences we complete */
-            if(ss_off[ss_i] >= sis_off[sis_i])
-                int_sel_off = ss_sel_off;
-            else
-                int_sel_off = sis_off[sis_i] - ss_off[ss_i] + ss_sel_off;
-            if((ss_off[ss_i] + (hsize_t)ss_len[ss_i]) <= (sis_off[sis_i]
-                    + (hsize_t)sis_len[sis_i])) {
-                int_len = (size_t)((hsize_t)ss_len[ss_i] + ss_sel_off - int_sel_off);
-                advance_ss = TRUE;
-            } /* end if */
-            else
-                int_len = (size_t)(sis_off[sis_i] + (hsize_t)sis_len[sis_i] - ss_off[ss_i] + ss_sel_off - int_sel_off);
-            if((ss_off[ss_i] + (hsize_t)ss_len[ss_i]) >= (sis_off[sis_i]
-                    + (hsize_t)sis_len[sis_i]))
-                advance_sis = TRUE;
-
-            /* Project intersection sequence to destination selection */
-            while(int_len > (size_t)0) {
-                while(ds_sel_off + (hsize_t)ds_len[ds_i] <= int_sel_off) {
-                    /* Intersection is not projected to this destination
-                     * sequence, advance destination space */
-                    ds_sel_off += (hsize_t)ds_len[ds_i];
-                    if(++ds_i == ds_nseq) {
-                        HDassert(ds_nelem > 0);
-
-                        /* Try to grab more sequences from dst_space */
-                        if(H5S_SELECT_GET_SEQ_LIST(dst_space, 0u, ds_iter, H5S_PROJECT_INTERSECT_NSEQS, ds_nelem, &ds_nseq, &nelem, ds_off, ds_len) < 0)
-                            HGOTO_ERROR(H5E_INTERNAL, H5E_UNSUPPORTED, FAIL, "sequence length generation failed")
-                        HDassert(ds_len[0] > 0);
-
-                        /* Update ss_nelem */
-                        HDassert(nelem > 0);
-                        HDassert(nelem <= ds_nelem);
-                        ds_nelem -= nelem;
-
-                        /* Reset source space index */
-                        ds_i = 0;
-                    } /* end if */
-                } /* end while */
-
-                /* Add sequence to projected space */
-                HDassert(ds_sel_off <= int_sel_off);
-                proj_off = ds_off[ds_i] + int_sel_off - ds_sel_off;
-                proj_len = proj_len_rem = (size_t)MIN(int_len,
-                        (size_t)(ds_sel_off + (hsize_t)ds_len[ds_i]
-                        - int_sel_off));
-
-                /* Add to span tree */
-                while(proj_len_rem > (size_t)0) {
-                    /* Check for more than one full row (in every dim) and
-                     * append multiple spans at once? -NAF */
-                    /* Append spans in higher dimensions if we're going ouside
-                     * the plane of the span currently being built (i.e. it's
-                     * finished being built) */
-                    for(i = proj_rank - 1; ((i > 0)
-                            && ((proj_off / proj_down_dims[i - 1])
-                            != curr_span_up_dim[i - 1])); i--) {
-                        if(curr_span_tree[i]) {
-                            HDassert(prev_span[i]);
-
-                            /* Append complete lower dimension span tree to
-                             * current dimension */
-                            low = curr_span_up_dim[i - 1] % proj_space->extent.size[i - 1];
-                            if(H5S__hyper_append_span(&prev_span[i - 1], &curr_span_tree[i - 1], low, low, curr_span_tree[i], NULL) < 0)
-                                HGOTO_ERROR(H5E_DATASPACE, H5E_CANTAPPEND, FAIL, "can't allocate hyperslab span")
+        /* Simply point to existing span tree */
+        ss_span_info = src_space->select.sel_info.hslab->span_lst;
+    } /* end if */
+    else {
+        /* Create temporary span tree from all selection */
+        HDassert(H5S_GET_SELECT_TYPE(src_space) == H5S_SEL_ALL);
 
-                            /* Reset lower dimension's span tree and previous
-                             * span since we just committed it and will start
-                             * over with a new one */
-                            if(H5S__hyper_free_span_info(curr_span_tree[i]) < 0)
-                                HGOTO_ERROR(H5E_DATASPACE, H5E_CANTFREE, FAIL, "can't free span info")
-                            curr_span_tree[i] = NULL;
-                            prev_span[i] = NULL;
-                        } /* end if */
+        if(NULL == (ss_span_info_buf = H5S__hyper_make_spans(H5S_GET_EXTENT_NDIMS(src_space),
+                H5S_hyper_zeros_g, H5S_hyper_zeros_g, H5S_hyper_ones_g, src_space->extent.size)))
+            HGOTO_ERROR(H5E_DATASPACE, H5E_CANTINIT, FAIL, "can't create span tree for ALL source space")
+        ss_span_info = ss_span_info_buf;
+    } /* end else */
 
-                        /* Update curr_span_up_dim */
-                        curr_span_up_dim[i - 1] = proj_off / proj_down_dims[i - 1];
-                    } /* end for */
+    /* Set up ds_span_info */
+    if(H5S_GET_SELECT_TYPE(dst_space) == H5S_SEL_HYPERSLABS) {
+        /* Make certain the selection has a span tree */
+        if(NULL == dst_space->select.sel_info.hslab->span_lst)
+            if(H5S__hyper_generate_spans((H5S_t *)dst_space) < 0)  /* Casting away const OK -NAF */
+                HGOTO_ERROR(H5E_DATASPACE, H5E_UNINITIALIZED, FAIL, "can't construct span tree for dsetination hyperslab selection")
 
-                    /* Compute bounds for new span in lowest dimension */
-                    low = proj_off % proj_space->extent.size[proj_rank - 1];
-                    span_len = MIN(proj_len_rem,
-                            (size_t)(proj_space->extent.size[proj_rank - 1]
-                            - low));
-                    HDassert(proj_len_rem >= span_len);
-                    high = low + (hsize_t)span_len - (hsize_t)1;
+        /* Simply point to existing span tree */
+        ds_span_info = dst_space->select.sel_info.hslab->span_lst;
+    } /* end if */
+    else {
+        /* Create temporary span tree from all selection */
+        HDassert(H5S_GET_SELECT_TYPE(dst_space) == H5S_SEL_ALL);
 
-                    /* Append span in lowest dimension */
-                    if(H5S__hyper_append_span(&prev_span[proj_rank - 1], &curr_span_tree[proj_rank - 1], low, high, NULL, NULL) < 0)
-                        HGOTO_ERROR(H5E_DATASPACE, H5E_CANTAPPEND, FAIL, "can't allocate hyperslab span")
+        if(NULL == (ds_span_info_buf = H5S__hyper_make_spans(H5S_GET_EXTENT_NDIMS(dst_space),
+                H5S_hyper_zeros_g, H5S_hyper_zeros_g, H5S_hyper_ones_g, dst_space->extent.size)))
+            HGOTO_ERROR(H5E_DATASPACE, H5E_CANTINIT, FAIL, "can't create span tree for ALL destination space")
+        ds_span_info = ds_span_info_buf;
+    } /* end else */
 
-                    /* Update remaining offset and length */
-                    proj_off += (hsize_t)span_len;
-                    proj_len_rem -= span_len;
-                } /* end while */
+    /* Make certain the source intersect selection has a span tree */
+    if(NULL == src_intersect_space->select.sel_info.hslab->span_lst)
+        if(H5S__hyper_generate_spans((H5S_t *)src_intersect_space) < 0)  /* Casting away const OK -NAF */
+            HGOTO_ERROR(H5E_DATASPACE, H5E_UNINITIALIZED, FAIL, "can't construct span tree for source intersect hyperslab selection")
+
+    /* Initialize udata */
+    /* We will use op_info[0] for nelem and op_info[1] for copied spans */
+    HDmemset(&udata, 0, sizeof(udata));
+    udata.ds_span[0] = ds_span_info->head;
+    udata.ds_low[0] = udata.ds_span[0]->low;
+    udata.ss_rank = H5S_GET_EXTENT_NDIMS(src_space);
+    udata.ds_rank = H5S_GET_EXTENT_NDIMS(dst_space);
+    udata.op_gen = H5S__hyper_get_op_gen();
+    udata.share_selection = share_selection;
+
+    /* Iterate over selections and build projected span tree */
+    if(H5S__hyper_proj_int_iterate(ss_span_info, src_intersect_space->select.sel_info.hslab->span_lst, 1, 0, &udata) < 0)
+        HGOTO_ERROR(H5E_DATASPACE, H5E_CANTCOMPARE, FAIL, "selection iteration failed")
 
-                /* Update intersection sequence */
-                int_sel_off += (hsize_t)proj_len;
-                int_len -= proj_len;
-            } /* end while */
-        } /* end else */
-    } /* end while */
+    /* Remove current selection from proj_space */
+    if(H5S_SELECT_RELEASE(proj_space) < 0)
+        HGOTO_ERROR(H5E_DATASPACE, H5E_CANTDELETE, FAIL, "can't release selection")
 
-loop_end:
-    /* Add remaining spans to span tree */
-    for(i = proj_rank - 1; i > 0; i--)
-        if(curr_span_tree[i]) {
-            HDassert(prev_span[i]);
+    /* Check for elements in projected space */
+    if(udata.ps_span_info[0]) {
+        /* Allocate space for the hyperslab selection information (note this sets
+         * diminfo_valid to FALSE, diminfo arrays to 0, and span list to NULL) */
+        if(NULL == (proj_space->select.sel_info.hslab = H5FL_CALLOC(H5S_hyper_sel_t)))
+            HGOTO_ERROR(H5E_DATASPACE, H5E_CANTALLOC, FAIL, "can't allocate hyperslab info")
 
-            /* Append remaining span tree to higher dimension */
-            low = curr_span_up_dim[i - 1] % proj_space->extent.size[i - 1];
-            if(H5S__hyper_append_span(&prev_span[i - 1], &curr_span_tree[i - 1], low, low, curr_span_tree[i], NULL) < 0)
-                HGOTO_ERROR(H5E_DATASPACE, H5E_CANTAPPEND, FAIL, "can't allocate hyperslab span")
+        /* Set selection type */
+        proj_space->select.type = H5S_sel_hyper;
 
-            /* Reset span tree */
-            if(H5S__hyper_free_span_info(curr_span_tree[i]) < 0)
-                HGOTO_ERROR(H5E_DATASPACE, H5E_CANTFREE, FAIL, "can't free span info")
-            curr_span_tree[i] = NULL;
-        } /* end if */
+        /* Set unlim_dim */
+        proj_space->select.sel_info.hslab->unlim_dim = -1;
 
-    /* Add span tree to proj_space */
-    if(curr_span_tree[0]) {
-        proj_space->select.sel_info.hslab->span_lst = curr_span_tree[0];
-        curr_span_tree[0] = NULL;
+        /* Set span tree */
+        proj_space->select.sel_info.hslab->span_lst = udata.ps_span_info[0];
+        udata.ps_span_info[0] = NULL;
 
         /* Set the number of elements in current selection */
         proj_space->select.num_elem = H5S__hyper_spans_nelem(proj_space->select.sel_info.hslab->span_lst);
 
-        /* Attempt to rebuild "optimized" start/stride/count/block information.
-         * from resulting hyperslab span tree */
+        /* Attempt to build "optimized" start/stride/count/block information
+         * from resulting hyperslab span tree.
+         */
         H5S__hyper_rebuild(proj_space);
     } /* end if */
     else
@@ -9699,154 +11425,42 @@ loop_end:
             HGOTO_ERROR(H5E_DATASPACE, H5E_CANTDELETE, FAIL, "can't convert selection")
 
 done:
-    /* Release source selection iterator */
-    if(ss_iter_init && H5S_SELECT_ITER_RELEASE(ss_iter) < 0)
-        HDONE_ERROR(H5E_DATASPACE, H5E_CANTRELEASE, FAIL, "unable to release selection iterator")
-    if(ss_iter)
-        ss_iter = H5FL_FREE(H5S_sel_iter_t, ss_iter);
-
-    /* Release destination selection iterator */
-    if(ds_iter_init && H5S_SELECT_ITER_RELEASE(ds_iter) < 0)
-        HDONE_ERROR(H5E_DATASPACE, H5E_CANTRELEASE, FAIL, "unable to release selection iterator")
-    if(ds_iter)
-        ds_iter = H5FL_FREE(H5S_sel_iter_t, ds_iter);
-
-    /* Release source intersect selection iterator */
-    if(sis_iter_init && H5S_SELECT_ITER_RELEASE(sis_iter) < 0)
-        HDONE_ERROR(H5E_DATASPACE, H5E_CANTRELEASE, FAIL, "unable to release selection iterator")
-    if(sis_iter)
-        sis_iter = H5FL_FREE(H5S_sel_iter_t, sis_iter);
+    /* Free ss_span_info_buf */
+    if(ss_span_info_buf) {
+        H5S__hyper_free_span_info(ss_span_info_buf);
+        ss_span_info_buf = NULL;
+    } /* end if */
+
+    /* Free ds_span_info_buf */
+    if(ds_span_info_buf) {
+        H5S__hyper_free_span_info(ds_span_info_buf);
+        ds_span_info_buf = NULL;
+    } /* end if */
 
     /* Cleanup on error */
     if(ret_value < 0) {
-        /* Remove current selection from proj_space */
-        if(H5S_SELECT_RELEASE(proj_space) < 0)
-            HDONE_ERROR(H5E_DATASPACE, H5E_CANTDELETE, FAIL, "can't release selection")
+        unsigned u;
 
         /* Free span trees */
-        for(i = 0; i < proj_rank; i++)
-            if(curr_span_tree[i]) {
-                if(H5S__hyper_free_span_info(curr_span_tree[i]) < 0)
-                    HGOTO_ERROR(H5E_DATASPACE, H5E_CANTFREE, FAIL, "can't free span info")
-                curr_span_tree[i] = NULL;
+        for(u = 0; u < udata.ds_rank; u++)
+            if(udata.ps_span_info[u]) {
+                H5S__hyper_free_span_info(udata.ps_span_info[u]);
+                udata.ps_span_info[u] = NULL;
             } /* end if */
     } /* end if */
 
-    FUNC_LEAVE_NOAPI(ret_value)
-} /* end H5S__hyper_project_intersection() */
-
-
-/*--------------------------------------------------------------------------
- NAME
-    H5S__hyper_subtract
- PURPOSE
-    Subtract one hyperslab selection from another
- USAGE
-    herr_t H5S__hyper_subtract(space,subtract_space)
-        H5S_t *space;           IN/OUT: Selection to be operated on
-        H5S_t *subtract_space;  IN: Selection that will be subtracted from space
- RETURNS
-    Non-negative on success/Negative on failure.
- DESCRIPTION
-    Removes any and all portions of space that are also present in
-    subtract_space.  In essence, performs an A_NOT_B operation with the
-    two selections.
-
-    Note this function basically duplicates a subset of the functionality
-    of H5S_select_select().  It should probably be removed when that
-    function is enabled.
- GLOBAL VARIABLES
- COMMENTS, BUGS, ASSUMPTIONS
- EXAMPLES
- REVISION LOG
---------------------------------------------------------------------------*/
-herr_t
-H5S__hyper_subtract(H5S_t *space, H5S_t *subtract_space)
-{
-    H5S_hyper_span_info_t *a_not_b = NULL;  /* Span tree for hyperslab spans in old span tree and not in new span tree */
-    H5S_hyper_span_info_t *a_and_b = NULL;  /* Span tree for hyperslab spans in both old and new span trees */
-    H5S_hyper_span_info_t *b_not_a = NULL;  /* Span tree for hyperslab spans in new span tree and not in old span tree */
-    herr_t      ret_value = SUCCEED;        /* Return value */
-
-    FUNC_ENTER_NOAPI_NOINIT
-
-    /* Check args */
-    HDassert(space);
-    HDassert(subtract_space);
-
-    /* Check that the space selections both have span trees */
-    if(space->select.sel_info.hslab->span_lst == NULL)
-        if(H5S__hyper_generate_spans(space) < 0)
-            HGOTO_ERROR(H5E_DATASPACE, H5E_UNINITIALIZED, FAIL, "dataspace does not have span tree")
-    if(subtract_space->select.sel_info.hslab->span_lst == NULL)
-        if(H5S__hyper_generate_spans(subtract_space) < 0)
-            HGOTO_ERROR(H5E_DATASPACE, H5E_UNINITIALIZED, FAIL, "dataspace does not have span tree")
-
-    /* Generate lists of spans which overlap and don't overlap */
-    if(H5S__hyper_clip_spans(space->select.sel_info.hslab->span_lst, subtract_space->select.sel_info.hslab->span_lst, &a_not_b, &a_and_b, &b_not_a)<0)
-        HGOTO_ERROR(H5E_DATASPACE, H5E_CANTCLIP, FAIL, "can't clip hyperslab information")
-
-    /* Reset the other dataspace selection information */
-    if(H5S_SELECT_RELEASE(space) < 0)
-        HGOTO_ERROR(H5E_DATASPACE, H5E_CANTDELETE, FAIL, "can't release selection")
-
-    /* Allocate space for the hyperslab selection information */
-    if((space->select.sel_info.hslab = H5FL_CALLOC(H5S_hyper_sel_t)) == NULL)
-        HGOTO_ERROR(H5E_DATASPACE, H5E_NOSPACE, FAIL, "can't allocate hyperslab info")
-    space->select.sel_info.hslab->diminfo_valid = H5S_DIMINFO_VALID_NO;
-
-    /* Set unlim_dim */
-    space->select.sel_info.hslab->unlim_dim = -1;
-
-    /* Check for anything returned in a_not_b */
-    if(a_not_b) {
-        /* Update spans in space */
-        space->select.sel_info.hslab->span_lst = a_not_b;
-        a_not_b = NULL;
-
-        /* Update number of elements */
-        space->select.num_elem = H5S__hyper_spans_nelem(space->select.sel_info.hslab->span_lst);
-
-        /* Attempt to rebuild "optimized" start/stride/count/block information.
-         * from resulting hyperslab span tree */
-        H5S__hyper_rebuild(space);
-    } /* end if */
-    else {
-        H5S_hyper_span_info_t *spans;     /* Empty hyperslab span tree */
-
-        /* Set number of elements */
-        space->select.num_elem = 0;
+#ifndef NDEBUG
+    /* Verify there are no more span trees */
+    {
+        unsigned u;
 
-        /* Allocate a span info node */
-        if(NULL == (spans = H5FL_MALLOC(H5S_hyper_span_info_t)))
-            HGOTO_ERROR(H5E_DATASPACE, H5E_CANTALLOC, FAIL, "can't allocate hyperslab span")
-
-        /* Set the reference count */
-        spans->count = 1;
-
-        /* Reset the scratch pad space */
-        spans->scratch = 0;
-
-        /* Set to empty tree */
-        spans->head = NULL;
-
-        /* Set pointer to empty span tree */
-        space->select.sel_info.hslab->span_lst = spans;
-    } /* end if */
-
-done:
-    /* Free span trees */
-    if(a_and_b)
-        H5S__hyper_free_span_info(a_and_b);
-    if(b_not_a)
-        H5S__hyper_free_span_info(b_not_a);
-    if(a_not_b) {
-        HDassert(ret_value < 0);
-        H5S__hyper_free_span_info(b_not_a);
-    } /* end if */
+        for(u = 0; u < H5S_MAX_RANK; u++)
+            HDassert(!udata.ps_span_info[u]);
+    } /* end block */
+#endif /* NDEBUG */
 
     FUNC_LEAVE_NOAPI(ret_value)
-} /* end H5S__hyper_subtract() */
+} /* end H5S__hyper_project_intersection() */
 
 
 /*--------------------------------------------------------------------------
@@ -10018,6 +11632,13 @@ H5S_hyper_clip_unlim(H5S_t *space, hsize_t clip_size)
             hslab->diminfo_valid = H5S_DIMINFO_VALID_YES;
     } /* end else */
 
+    /* Update the upper bound, if the diminfo is valid */
+    if(hslab && (H5S_DIMINFO_VALID_YES == hslab->diminfo_valid))
+        hslab->diminfo.high_bounds[orig_unlim_dim] =
+                hslab->diminfo.opt[orig_unlim_dim].start +
+                hslab->diminfo.opt[orig_unlim_dim].stride * (hslab->diminfo.opt[orig_unlim_dim].count - 1) +
+                (hslab->diminfo.opt[orig_unlim_dim].block - 1);
+
 done:
     FUNC_LEAVE_NOAPI(ret_value)
 } /* end H5S_hyper_clip_unlim() */