[svn-r14307] Description:

    - Extracted common code from H5D_select_read/H5D_select_write into single
        routine (H5D_select_io) and made H5D_select_read/H5D_select_write
        "gateway" routines, passing I/O buffer to operate on in "op" struct.
    - Create optimized pathway in H5D_select_io for I/O operations on single
        elements.
    - Make "get linear offset of first element" callback for each type of
        selection (used in "optimized pathway", above)

Tested on:
        FreeBSD/32 6.2 (duty) in debug mode
        FreeBSD/64 6.2 (liberty) w/C++ & FORTRAN, in debug mode
        Linux/32 2.6 (kagiso) w/PGI compilers, w/C++ & FORTRAN, w/threadsafe,
                                in debug mode
        Linux/64-amd64 2.6 (smirom) w/default API=1.6.x, w/C++ & FORTRAN,
                                in production mode
        Linux/64-ia64 2.6 (cobalt) w/Intel compilers, w/C++ & FORTRAN,
                                in production mode
        Solaris/32 2.10 (linew) w/deprecated symbols disabled, w/C++ & FORTRAN,
                                w/szip filter, in production mode
        Mac OS X/32 10.4.10 (amazon) in debug mode
        Linux/64-ia64 2.4 (tg-login3) w/parallel, w/FORTRAN, in production mode

9 files changed, 542 insertions, 256 deletions

diff --git a/src/H5Dselect.c b/src/H5Dselect.c
index 105b4e5..f08672f 100644
--- a/src/H5Dselect.c
+++ b/src/H5Dselect.c
@@ -46,6 +46,18 @@
 /* Local Prototypes */
 /********************/
 
+/* Struct for holding the vectorized I/O operation buffers "loosely" */
+typedef struct {
+    enum {
+        H5S_SELECT_READ,                /* Read selection */
+        H5S_SELECT_WRITE                /* Write selection */
+    } op_type;
+    union {
+        void *rbuf;                          /* Buffer for read */
+        const void *wbuf;                    /* Buffer to write */
+    } u;
+} H5D_select_buf_t;
+
 /*********************/
 /* Package Variables */
 /*********************/
@@ -419,153 +431,199 @@ done:
 
 
 /*-------------------------------------------------------------------------
- * Function:	H5D_select_read
+ * Function:	H5D_select_io
  *
- * Purpose:	Reads directly from file into application memory.
+ * Purpose:	Perform I/O directly from application memory and a file
  *
  * Return:	Non-negative on success/Negative on failure
  *
  * Programmer:	Quincey Koziol
- *              Tuesday, July 23, 2002
+ *              Tuesday, November 27, 2007
  *
  *-------------------------------------------------------------------------
  */
-herr_t
-H5D_select_read(H5D_io_info_t *io_info,
+static herr_t
+H5D_select_io(H5D_io_info_t *io_info,
     size_t nelmts, size_t elmt_size,
     const H5S_t *file_space, const H5S_t *mem_space,
     haddr_t addr, void *chunk/*in*/,
-    void *buf/*out*/)
+    const H5D_select_buf_t *io_buf)
 {
     H5S_sel_iter_t mem_iter;    /* Memory selection iteration info */
-    hbool_t mem_iter_init=0;    /* Memory selection iteration info has been initialized */
+    hbool_t mem_iter_init = 0;  /* Memory selection iteration info has been initialized */
     H5S_sel_iter_t file_iter;   /* File selection iteration info */
-    hbool_t file_iter_init=0;	/* File selection iteration info has been initialized */
+    hbool_t file_iter_init = 0;	/* File selection iteration info has been initialized */
     hsize_t _mem_off[H5D_IO_VECTOR_SIZE];      /* Array to store sequence offsets in memory */
-    hsize_t *mem_off=NULL;      /* Pointer to sequence offsets in memory */
+    hsize_t *mem_off = NULL;    /* Pointer to sequence offsets in memory */
     hsize_t _file_off[H5D_IO_VECTOR_SIZE];     /* Array to store sequence offsets in the file */
-    hsize_t *file_off=NULL;     /* Pointer to sequence offsets in the file */
+    hsize_t *file_off = NULL;   /* Pointer to sequence offsets in the file */
     size_t _mem_len[H5D_IO_VECTOR_SIZE];       /* Array to store sequence lengths in memory */
-    size_t *mem_len=NULL;       /* Pointer to sequence lengths in memory */
+    size_t *mem_len = NULL;     /* Pointer to sequence lengths in memory */
     size_t _file_len[H5D_IO_VECTOR_SIZE];      /* Array to store sequence lengths in the file */
-    size_t *file_len=NULL;      /* Pointer to sequence lengths in the file */
-    size_t mem_nseq;            /* Number of sequences generated in the file */
-    size_t file_nseq;           /* Number of sequences generated in memory */
-    size_t mem_nelem;           /* Number of elements used in memory sequences */
-    size_t file_nelem;          /* Number of elements used in file sequences */
+    size_t *file_len = NULL;    /* Pointer to sequence lengths in the file */
     size_t curr_mem_seq;        /* Current memory sequence to operate on */
     size_t curr_file_seq;       /* Current file sequence to operate on */
+    size_t mem_nseq;            /* Number of sequences generated in the file */
+    size_t file_nseq;           /* Number of sequences generated in memory */
     ssize_t tmp_file_len;       /* Temporary number of bytes in file sequence */
-    herr_t ret_value=SUCCEED;   /* Return value */
+    herr_t ret_value = SUCCEED; /* Return value */
 
-    FUNC_ENTER_NOAPI(H5D_select_read, FAIL);
+    FUNC_ENTER_NOAPI(H5D_select_io, FAIL)
 
     /* Check args */
-    assert(io_info);
-    assert(io_info->dset);
-    assert(io_info->dxpl_cache);
-    assert(io_info->store);
-    assert(buf);
-    assert(TRUE==H5P_isa_class(io_info->dxpl_id,H5P_DATASET_XFER));
-
-    /* Initialize file iterator */
-    if (H5S_select_iter_init(&file_iter, file_space, elmt_size)<0)
-        HGOTO_ERROR (H5E_DATASPACE, H5E_CANTINIT, FAIL, "unable to initialize selection iterator");
-    file_iter_init=1;	/* File selection iteration info has been initialized */
-
-    /* Initialize memory iterator */
-    if (H5S_select_iter_init(&mem_iter, mem_space, elmt_size)<0)
-        HGOTO_ERROR (H5E_DATASPACE, H5E_CANTINIT, FAIL, "unable to initialize selection iterator");
-    mem_iter_init=1;	/* Memory selection iteration info has been initialized */
+    HDassert(io_info);
+    HDassert(io_info->dset);
+    HDassert(io_info->store);
+    HDassert(TRUE == H5P_isa_class(io_info->dxpl_id, H5P_DATASET_XFER));
+    HDassert(io_buf->u.rbuf);
 
     /* Allocate the vector I/O arrays */
     if(io_info->dxpl_cache->vec_size != H5D_IO_VECTOR_SIZE) {
-        if((mem_len = H5FL_SEQ_MALLOC(size_t,io_info->dxpl_cache->vec_size))==NULL)
-            HGOTO_ERROR(H5E_RESOURCE, H5E_NOSPACE, FAIL, "can't allocate I/O length vector array");
-        if((mem_off = H5FL_SEQ_MALLOC(hsize_t,io_info->dxpl_cache->vec_size))==NULL)
-            HGOTO_ERROR(H5E_RESOURCE, H5E_NOSPACE, FAIL, "can't allocate I/O offset vector array");
-        if((file_len = H5FL_SEQ_MALLOC(size_t,io_info->dxpl_cache->vec_size))==NULL)
-            HGOTO_ERROR(H5E_RESOURCE, H5E_NOSPACE, FAIL, "can't allocate I/O length vector array");
-        if((file_off = H5FL_SEQ_MALLOC(hsize_t,io_info->dxpl_cache->vec_size))==NULL)
-            HGOTO_ERROR(H5E_RESOURCE, H5E_NOSPACE, FAIL, "can't allocate I/O offset vector array");
+        if(NULL == (mem_len = H5FL_SEQ_MALLOC(size_t,io_info->dxpl_cache->vec_size)))
+            HGOTO_ERROR(H5E_RESOURCE, H5E_NOSPACE, FAIL, "can't allocate I/O length vector array")
+        if(NULL == (mem_off = H5FL_SEQ_MALLOC(hsize_t,io_info->dxpl_cache->vec_size)))
+            HGOTO_ERROR(H5E_RESOURCE, H5E_NOSPACE, FAIL, "can't allocate I/O offset vector array")
+        if(NULL == (file_len = H5FL_SEQ_MALLOC(size_t,io_info->dxpl_cache->vec_size)))
+            HGOTO_ERROR(H5E_RESOURCE, H5E_NOSPACE, FAIL, "can't allocate I/O length vector array")
+        if(NULL == (file_off = H5FL_SEQ_MALLOC(hsize_t,io_info->dxpl_cache->vec_size)))
+            HGOTO_ERROR(H5E_RESOURCE, H5E_NOSPACE, FAIL, "can't allocate I/O offset vector array")
     } /* end if */
     else {
-        mem_len=_mem_len;
-        mem_off=_mem_off;
-        file_len=_file_len;
-        file_off=_file_off;
+        mem_len = _mem_len;
+        mem_off = _mem_off;
+        file_len = _file_len;
+        file_off = _file_off;
     } /* end else */
 
-    /* Initialize sequence counts */
-    curr_mem_seq=curr_file_seq=0;
-    mem_nseq=file_nseq=0;
-
-    /* Loop, until all bytes are processed */
-    while(nelmts>0) {
-        /* Check if more file sequences are needed */
-        if(curr_file_seq>=file_nseq) {
-            /* Get sequences for file selection */
-            if(H5S_SELECT_GET_SEQ_LIST(file_space,H5S_GET_SEQ_LIST_SORTED,&file_iter,io_info->dxpl_cache->vec_size,nelmts,&file_nseq,&file_nelem,file_off,file_len)<0)
-                HGOTO_ERROR (H5E_INTERNAL, H5E_UNSUPPORTED, FAIL, "sequence length generation failed");
-
-            /* Start at the beginning of the sequences again */
-            curr_file_seq=0;
+    /* Check for only one element in selection */
+    if(nelmts == 1) {
+        /* Get offset of first element in selections */
+        if(H5S_SELECT_OFFSET(file_space, file_off) < 0)
+            HGOTO_ERROR(H5E_INTERNAL, H5E_UNSUPPORTED, FAIL, "can't retrieve file selection offset")
+        if(H5S_SELECT_OFFSET(mem_space, mem_off) < 0)
+            HGOTO_ERROR(H5E_INTERNAL, H5E_UNSUPPORTED, FAIL, "can't retrieve memory selection offset")
+
+        /* Set up necessary information for I/O operation */
+        file_nseq = mem_nseq = 1;
+        curr_mem_seq = curr_file_seq = 0;
+        *file_off *= elmt_size;
+        *mem_off *= elmt_size;
+        *file_len = *mem_len = elmt_size;
+
+        /* Perform I/O on memory and file sequences */
+        if(io_buf->op_type == H5S_SELECT_READ) {
+            if((tmp_file_len = (*io_info->ops.readvv)(io_info,
+                    file_nseq, &curr_file_seq, file_len, file_off,
+                    mem_nseq, &curr_mem_seq, mem_len, mem_off,
+                    addr, chunk, io_buf->u.rbuf)) < 0)
+                HGOTO_ERROR(H5E_DATASPACE, H5E_READERROR, FAIL, "read error")
         } /* end if */
-
-        /* Check if more memory sequences are needed */
-        if(curr_mem_seq>=mem_nseq) {
-            /* Get sequences for memory selection */
-            if(H5S_SELECT_GET_SEQ_LIST(mem_space,0,&mem_iter,io_info->dxpl_cache->vec_size,nelmts,&mem_nseq,&mem_nelem,mem_off,mem_len)<0)
-                HGOTO_ERROR (H5E_INTERNAL, H5E_UNSUPPORTED, FAIL, "sequence length generation failed");
-
-            /* Start at the beginning of the sequences again */
-            curr_mem_seq=0;
-        } /* end if */
-
-        /* Read file sequences into current memory sequence */
-        if ((tmp_file_len=(*io_info->ops.readvv)(io_info,
-                file_nseq, &curr_file_seq, file_len, file_off,
-                mem_nseq, &curr_mem_seq, mem_len, mem_off,
-                addr, chunk, buf))<0)
-            HGOTO_ERROR(H5E_DATASPACE, H5E_READERROR, FAIL, "read error");
+        else {
+            HDassert(io_buf->op_type == H5S_SELECT_WRITE);
+            if((tmp_file_len = (*io_info->ops.writevv)(io_info,
+                    file_nseq, &curr_file_seq, file_len, file_off,
+                    mem_nseq, &curr_mem_seq, mem_len, mem_off,
+                    addr, chunk, io_buf->u.wbuf)) < 0)
+                HGOTO_ERROR(H5E_DATASPACE, H5E_WRITEERROR, FAIL, "write error")
+        } /* end else */
 
         /* Decrement number of elements left to process */
-        assert((tmp_file_len%elmt_size)==0);
-        nelmts-=(tmp_file_len/elmt_size);
-    } /* end while */
+        HDassert((tmp_file_len % elmt_size) == 0);
+    } /* end if */
+    else {
+        size_t mem_nelem;           /* Number of elements used in memory sequences */
+        size_t file_nelem;          /* Number of elements used in file sequences */
+
+        /* Initialize file iterator */
+        if(H5S_select_iter_init(&file_iter, file_space, elmt_size) < 0)
+            HGOTO_ERROR(H5E_DATASPACE, H5E_CANTINIT, FAIL, "unable to initialize selection iterator")
+        file_iter_init = 1;	/* File selection iteration info has been initialized */
+
+        /* Initialize memory iterator */
+        if(H5S_select_iter_init(&mem_iter, mem_space, elmt_size) < 0)
+            HGOTO_ERROR(H5E_DATASPACE, H5E_CANTINIT, FAIL, "unable to initialize selection iterator")
+        mem_iter_init = 1;	/* Memory selection iteration info has been initialized */
+
+        /* Initialize sequence counts */
+        curr_mem_seq = curr_file_seq = 0;
+        mem_nseq = file_nseq = 0;
+
+        /* Loop, until all bytes are processed */
+        while(nelmts > 0) {
+            /* Check if more file sequences are needed */
+            if(curr_file_seq >= file_nseq) {
+                /* Get sequences for file selection */
+                if(H5S_SELECT_GET_SEQ_LIST(file_space, H5S_GET_SEQ_LIST_SORTED, &file_iter, io_info->dxpl_cache->vec_size, nelmts, &file_nseq, &file_nelem, file_off, file_len) < 0)
+                    HGOTO_ERROR(H5E_INTERNAL, H5E_UNSUPPORTED, FAIL, "sequence length generation failed")
+
+                /* Start at the beginning of the sequences again */
+                curr_file_seq = 0;
+            } /* end if */
+
+            /* Check if more memory sequences are needed */
+            if(curr_mem_seq >= mem_nseq) {
+                /* Get sequences for memory selection */
+                if(H5S_SELECT_GET_SEQ_LIST(mem_space, 0, &mem_iter, io_info->dxpl_cache->vec_size, nelmts, &mem_nseq, &mem_nelem, mem_off, mem_len) < 0)
+                    HGOTO_ERROR(H5E_INTERNAL, H5E_UNSUPPORTED, FAIL, "sequence length generation failed")
+
+                /* Start at the beginning of the sequences again */
+                curr_mem_seq = 0;
+            } /* end if */
+
+            /* Perform I/O on memory and file sequences */
+            if(io_buf->op_type == H5S_SELECT_READ) {
+                if((tmp_file_len = (*io_info->ops.readvv)(io_info,
+                        file_nseq, &curr_file_seq, file_len, file_off,
+                        mem_nseq, &curr_mem_seq, mem_len, mem_off,
+                        addr, chunk, io_buf->u.rbuf)) < 0)
+                    HGOTO_ERROR(H5E_DATASPACE, H5E_READERROR, FAIL, "read error")
+            } /* end if */
+            else {
+                HDassert(io_buf->op_type == H5S_SELECT_WRITE);
+                if((tmp_file_len = (*io_info->ops.writevv)(io_info,
+                        file_nseq, &curr_file_seq, file_len, file_off,
+                        mem_nseq, &curr_mem_seq, mem_len, mem_off,
+                        addr, chunk, io_buf->u.wbuf)) < 0)
+                    HGOTO_ERROR(H5E_DATASPACE, H5E_WRITEERROR, FAIL, "write error")
+            } /* end else */
+
+            /* Decrement number of elements left to process */
+            HDassert((tmp_file_len % elmt_size) == 0);
+            nelmts -= (tmp_file_len / elmt_size);
+        } /* end while */
+    } /* end else */
 
 done:
     /* Release file selection iterator */
-    if(file_iter_init) {
-        if (H5S_SELECT_ITER_RELEASE(&file_iter)<0)
-            HDONE_ERROR (H5E_DATASPACE, H5E_CANTRELEASE, FAIL, "unable to release selection iterator");
-    } /* end if */
+    if(file_iter_init)
+        if(H5S_SELECT_ITER_RELEASE(&file_iter) < 0)
+            HDONE_ERROR(H5E_DATASPACE, H5E_CANTRELEASE, FAIL, "unable to release selection iterator")
 
     /* Release memory selection iterator */
-    if(mem_iter_init) {
-        if (H5S_SELECT_ITER_RELEASE(&mem_iter)<0)
-            HDONE_ERROR (H5E_DATASPACE, H5E_CANTRELEASE, FAIL, "unable to release selection iterator");
-    } /* end if */
+    if(mem_iter_init)
+        if(H5S_SELECT_ITER_RELEASE(&mem_iter) < 0)
+            HDONE_ERROR(H5E_DATASPACE, H5E_CANTRELEASE, FAIL, "unable to release selection iterator")
 
     /* Free vector arrays */
     if(io_info->dxpl_cache->vec_size != H5D_IO_VECTOR_SIZE) {
-        if(file_len!=NULL)
-            H5FL_SEQ_FREE(size_t,file_len);
-        if(file_off!=NULL)
-            H5FL_SEQ_FREE(hsize_t,file_off);
-        if(mem_len!=NULL)
-            H5FL_SEQ_FREE(size_t,mem_len);
-        if(mem_off!=NULL)
-            H5FL_SEQ_FREE(hsize_t,mem_off);
+        if(file_len != NULL)
+            H5FL_SEQ_FREE(size_t, file_len);
+        if(file_off != NULL)
+            H5FL_SEQ_FREE(hsize_t, file_off);
+        if(mem_len != NULL)
+            H5FL_SEQ_FREE(size_t, mem_len);
+        if(mem_off != NULL)
+            H5FL_SEQ_FREE(hsize_t, mem_off);
     } /* end if */
-    FUNC_LEAVE_NOAPI(ret_value);
-} /* end H5D_select_read() */
+
+    FUNC_LEAVE_NOAPI(ret_value)
+} /* end H5D_select_io() */
 
 
 /*-------------------------------------------------------------------------
- * Function:	H5D_select_write
+ * Function:	H5D_select_read
  *
- * Purpose:	Writes directly from application memory into a file
+ * Purpose:	Reads directly from file into application memory.
  *
  * Return:	Non-negative on success/Negative on failure
  *
@@ -575,133 +633,63 @@ done:
  *-------------------------------------------------------------------------
  */
 herr_t
-H5D_select_write(H5D_io_info_t *io_info,
+H5D_select_read(H5D_io_info_t *io_info,
     size_t nelmts, size_t elmt_size,
     const H5S_t *file_space, const H5S_t *mem_space,
     haddr_t addr, void *chunk/*in*/,
-    const void *buf/*out*/)
+    void *buf/*out*/)
 {
-    H5S_sel_iter_t mem_iter;    /* Memory selection iteration info */
-    hbool_t mem_iter_init=0;    /* Memory selection iteration info has been initialized */
-    H5S_sel_iter_t file_iter;   /* File selection iteration info */
-    hbool_t file_iter_init=0;	/* File selection iteration info has been initialized */
-    hsize_t _mem_off[H5D_IO_VECTOR_SIZE];      /* Array to store sequence offsets in memory */
-    hsize_t *mem_off=NULL;      /* Pointer to sequence offsets in memory */
-    hsize_t _file_off[H5D_IO_VECTOR_SIZE];     /* Array to store sequence offsets in the file */
-    hsize_t *file_off=NULL;     /* Pointer to sequence offsets in the file */
-    size_t _mem_len[H5D_IO_VECTOR_SIZE];       /* Array to store sequence lengths in memory */
-    size_t *mem_len=NULL;       /* Pointer to sequence lengths in memory */
-    size_t _file_len[H5D_IO_VECTOR_SIZE];      /* Array to store sequence lengths in the file */
-    size_t *file_len=NULL;      /* Pointer to sequence lengths in the file */
-    size_t mem_nseq;            /* Number of sequences generated in the file */
-    size_t file_nseq;           /* Number of sequences generated in memory */
-    size_t mem_nelem;           /* Number of elements used in memory sequences */
-    size_t file_nelem;          /* Number of elements used in file sequences */
-    size_t curr_mem_seq;        /* Current memory sequence to operate on */
-    size_t curr_file_seq;       /* Current file sequence to operate on */
-    ssize_t tmp_file_len;       /* Temporary number of bytes in file sequence */
-    herr_t ret_value=SUCCEED;   /* Return value */
+    H5D_select_buf_t io_buf;      /* Selection I/O operation to perform */
+    herr_t ret_value = SUCCEED; /* Return value */
 
-    FUNC_ENTER_NOAPI(H5D_select_write, FAIL);
+    FUNC_ENTER_NOAPI(H5D_select_read, FAIL)
 
-    /* Check args */
-    assert(io_info);
-    assert(io_info->dset);
-    assert(io_info->store);
-    assert(TRUE==H5P_isa_class(io_info->dxpl_id,H5P_DATASET_XFER));
-    assert(buf);
-
-    /* Allocate the vector I/O arrays */
-    if(io_info->dxpl_cache->vec_size != H5D_IO_VECTOR_SIZE) {
-        if((mem_len = H5FL_SEQ_MALLOC(size_t,io_info->dxpl_cache->vec_size))==NULL)
-            HGOTO_ERROR(H5E_RESOURCE, H5E_NOSPACE, FAIL, "can't allocate I/O length vector array");
-        if((mem_off = H5FL_SEQ_MALLOC(hsize_t,io_info->dxpl_cache->vec_size))==NULL)
-            HGOTO_ERROR(H5E_RESOURCE, H5E_NOSPACE, FAIL, "can't allocate I/O offset vector array");
-        if((file_len = H5FL_SEQ_MALLOC(size_t,io_info->dxpl_cache->vec_size))==NULL)
-            HGOTO_ERROR(H5E_RESOURCE, H5E_NOSPACE, FAIL, "can't allocate I/O length vector array");
-        if((file_off = H5FL_SEQ_MALLOC(hsize_t,io_info->dxpl_cache->vec_size))==NULL)
-            HGOTO_ERROR(H5E_RESOURCE, H5E_NOSPACE, FAIL, "can't allocate I/O offset vector array");
-    } /* end if */
-    else {
-        mem_len=_mem_len;
-        mem_off=_mem_off;
-        file_len=_file_len;
-        file_off=_file_off;
-    } /* end else */
-
-    /* Initialize file iterator */
-    if (H5S_select_iter_init(&file_iter, file_space, elmt_size)<0)
-        HGOTO_ERROR (H5E_DATASPACE, H5E_CANTINIT, FAIL, "unable to initialize selection iterator");
-    file_iter_init=1;	/* File selection iteration info has been initialized */
-
-    /* Initialize memory iterator */
-    if (H5S_select_iter_init(&mem_iter, mem_space, elmt_size)<0)
-        HGOTO_ERROR (H5E_DATASPACE, H5E_CANTINIT, FAIL, "unable to initialize selection iterator");
-    mem_iter_init=1;	/* Memory selection iteration info has been initialized */
+    /* Construct proper I/O operation */
+    io_buf.op_type = H5S_SELECT_READ;
+    io_buf.u.rbuf = buf;
 
-    /* Initialize sequence counts */
-    curr_mem_seq=curr_file_seq=0;
-    mem_nseq=file_nseq=0;
+    /* Call generic selection operation */
+    if(H5D_select_io(io_info, nelmts, elmt_size, file_space, mem_space, addr, chunk, &io_buf) < 0)
+        HGOTO_ERROR(H5E_DATASPACE, H5E_READERROR, FAIL, "read error")
 
-    /* Loop, until all bytes are processed */
-    while(nelmts>0) {
-        /* Check if more file sequences are needed */
-        if(curr_file_seq>=file_nseq) {
-            /* Get sequences for file selection */
-            if(H5S_SELECT_GET_SEQ_LIST(file_space,H5S_GET_SEQ_LIST_SORTED,&file_iter,io_info->dxpl_cache->vec_size,nelmts,&file_nseq,&file_nelem,file_off,file_len)<0)
-                HGOTO_ERROR (H5E_INTERNAL, H5E_UNSUPPORTED, FAIL, "sequence length generation failed");
-
-            /* Start at the beginning of the sequences again */
-            curr_file_seq=0;
-        } /* end if */
+done:
+    FUNC_LEAVE_NOAPI(ret_value)
+} /* end H5D_select_read() */
 
-        /* Check if more memory sequences are needed */
-        if(curr_mem_seq>=mem_nseq) {
-            /* Get sequences for memory selection */
-            if(H5S_SELECT_GET_SEQ_LIST(mem_space,0,&mem_iter,io_info->dxpl_cache->vec_size,nelmts,&mem_nseq,&mem_nelem,mem_off,mem_len)<0)
-                HGOTO_ERROR (H5E_INTERNAL, H5E_UNSUPPORTED, FAIL, "sequence length generation failed");
+
+/*-------------------------------------------------------------------------
+ * Function:	H5D_select_write
+ *
+ * Purpose:	Writes directly from application memory into a file
+ *
+ * Return:	Non-negative on success/Negative on failure
+ *
+ * Programmer:	Quincey Koziol
+ *              Tuesday, July 23, 2002
+ *
+ *-------------------------------------------------------------------------
+ */
+herr_t
+H5D_select_write(H5D_io_info_t *io_info,
+    size_t nelmts, size_t elmt_size,
+    const H5S_t *file_space, const H5S_t *mem_space,
+    haddr_t addr, void *chunk/*in*/,
+    const void *buf/*out*/)
+{
+    H5D_select_buf_t io_buf;      /* Selection I/O operation to perform */
+    herr_t ret_value = SUCCEED; /* Return value */
 
-            /* Start at the beginning of the sequences again */
-            curr_mem_seq=0;
-        } /* end if */
+    FUNC_ENTER_NOAPI(H5D_select_write, FAIL)
 
-        /* Write memory sequences into file sequences */
-        if ((tmp_file_len=(*io_info->ops.writevv)(io_info,
-                file_nseq, &curr_file_seq, file_len, file_off,
-                mem_nseq, &curr_mem_seq, mem_len, mem_off,
-                addr, chunk, buf))<0)
-            HGOTO_ERROR(H5E_DATASPACE, H5E_WRITEERROR, FAIL, "write error");
+    /* Construct proper I/O operation */
+    io_buf.op_type = H5S_SELECT_WRITE;
+    io_buf.u.wbuf = buf;
 
-        /* Decrement number of elements left to process */
-        assert((tmp_file_len%elmt_size)==0);
-        nelmts-=(tmp_file_len/elmt_size);
-    } /* end while */
+    /* Call generic selection operation */
+    if(H5D_select_io(io_info, nelmts, elmt_size, file_space, mem_space, addr, chunk, &io_buf) < 0)
+        HGOTO_ERROR(H5E_DATASPACE, H5E_WRITEERROR, FAIL, "write error")
 
 done:
-    /* Release file selection iterator */
-    if(file_iter_init) {
-        if (H5S_SELECT_ITER_RELEASE(&file_iter)<0)
-            HDONE_ERROR (H5E_DATASPACE, H5E_CANTRELEASE, FAIL, "unable to release selection iterator");
-    } /* end if */
-
-    /* Release memory selection iterator */
-    if(mem_iter_init) {
-        if (H5S_SELECT_ITER_RELEASE(&mem_iter)<0)
-            HDONE_ERROR (H5E_DATASPACE, H5E_CANTRELEASE, FAIL, "unable to release selection iterator");
-    } /* end if */
-
-    /* Free vector arrays */
-    if(io_info->dxpl_cache->vec_size != H5D_IO_VECTOR_SIZE) {
-        if(file_len!=NULL)
-            H5FL_SEQ_FREE(size_t,file_len);
-        if(file_off!=NULL)
-            H5FL_SEQ_FREE(hsize_t,file_off);
-        if(mem_len!=NULL)
-            H5FL_SEQ_FREE(size_t,mem_len);
-        if(mem_off!=NULL)
-            H5FL_SEQ_FREE(hsize_t,mem_off);
-    } /* end if */
-
-    FUNC_LEAVE_NOAPI(ret_value);
+    FUNC_LEAVE_NOAPI(ret_value)
 } /* end H5D_select_write() */
 
diff --git a/src/H5Sall.c b/src/H5Sall.c
index 5d01fec..c603251 100644
--- a/src/H5Sall.c
+++ b/src/H5Sall.c
@@ -42,6 +42,7 @@ static hssize_t H5S_all_serial_size(const H5S_t *space);
 static herr_t H5S_all_serialize(const H5S_t *space, uint8_t *buf);
 static herr_t H5S_all_deserialize(H5S_t *space, const uint8_t *buf);
 static herr_t H5S_all_bounds(const H5S_t *space, hsize_t *start, hsize_t *end);
+static herr_t H5S_all_offset(const H5S_t *space, hsize_t *off);
 static htri_t H5S_all_is_contiguous(const H5S_t *space);
 static htri_t H5S_all_is_single(const H5S_t *space);
 static htri_t H5S_all_is_regular(const H5S_t *space);
@@ -70,6 +71,7 @@ const H5S_select_class_t H5S_sel_all[1] = {{
     H5S_all_serialize,
     H5S_all_deserialize,
     H5S_all_bounds,
+    H5S_all_offset,
     H5S_all_is_contiguous,
     H5S_all_is_single,
     H5S_all_is_regular,
@@ -585,26 +587,61 @@ done:
 herr_t
 H5S_all_bounds(const H5S_t *space, hsize_t *start, hsize_t *end)
 {
-    int rank;                  /* Dataspace rank */
-    int i;                     /* index variable */
+    unsigned rank;                  /* Dataspace rank */
+    unsigned i;                     /* index variable */
 
-    FUNC_ENTER_NOAPI_NOFUNC(H5S_all_bounds);
+    FUNC_ENTER_NOAPI_NOFUNC(H5S_all_bounds)
 
-    assert(space);
-    assert(start);
-    assert(end);
+    HDassert(space);
+    HDassert(start);
+    HDassert(end);
 
     /* Get the dataspace extent rank */
-    rank=space->extent.rank;
+    rank = space->extent.rank;
 
     /* Just copy over the complete extent */
-    for(i=0; i<rank; i++) {
-        start[i]=0;
-        end[i]=space->extent.size[i]-1;
+    for(i = 0; i < rank; i++) {
+        start[i] = 0;
+        end[i] = space->extent.size[i] - 1;
     } /* end for */
 
-    FUNC_LEAVE_NOAPI(SUCCEED);
-}   /* H5Sget_all_bounds() */
+    FUNC_LEAVE_NOAPI(SUCCEED)
+}   /* H5S_all_bounds() */
+
+
+/*--------------------------------------------------------------------------
+ NAME
+    H5S_all_offset
+ PURPOSE
+    Gets the linear offset of the first element for the selection.
+ USAGE
+    herr_t H5S_all_offset(space, offset)
+        const H5S_t *space;     IN: Dataspace pointer of selection to query
+        hsize_t *offset;        OUT: Linear offset of first element in selection
+ RETURNS
+    Non-negative on success, negative on failure
+ DESCRIPTION
+    Retrieves the linear offset (in "units" of elements) of the first element
+    selected within the dataspace.
+ GLOBAL VARIABLES
+ COMMENTS, BUGS, ASSUMPTIONS
+    Calling this function on a "none" selection returns fail.
+ EXAMPLES
+ REVISION LOG
+--------------------------------------------------------------------------*/
+herr_t
+H5S_all_offset(const H5S_t *space, hsize_t *offset)
+{
+    FUNC_ENTER_NOAPI_NOFUNC(H5S_all_offset)
+
+    HDassert(space);
+    HDassert(offset);
+
+    /* 'All' selections always start at offset 0 */
+    *offset = 0;
+
+    FUNC_LEAVE_NOAPI(SUCCEED)
+}   /* H5S_all_offset() */
 
 
 /*--------------------------------------------------------------------------
diff --git a/src/H5Shyper.c b/src/H5Shyper.c
index 8acbfd5..9ca1fdc 100644
--- a/src/H5Shyper.c
+++ b/src/H5Shyper.c
@@ -57,6 +57,7 @@ static hssize_t H5S_hyper_serial_size(const H5S_t *space);
 static herr_t H5S_hyper_serialize(const H5S_t *space, uint8_t *buf);
 static herr_t H5S_hyper_deserialize(H5S_t *space, const uint8_t *buf);
 static herr_t H5S_hyper_bounds(const H5S_t *space, hsize_t *start, hsize_t *end);
+static herr_t H5S_hyper_offset(const H5S_t *space, hsize_t *offset);
 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);
@@ -90,6 +91,7 @@ const H5S_select_class_t H5S_sel_hyper[1] = {{
     H5S_hyper_serialize,
     H5S_hyper_deserialize,
     H5S_hyper_bounds,
+    H5S_hyper_offset,
     H5S_hyper_is_contiguous,
     H5S_hyper_is_single,
     H5S_hyper_is_regular,
@@ -2708,6 +2710,114 @@ done:
 
 /*--------------------------------------------------------------------------
  NAME
+    H5S_hyper_offset
+ PURPOSE
+    Gets the linear offset of the first element for the selection.
+ USAGE
+    herr_t H5S_hyper_offset(space, offset)
+        const H5S_t *space;     IN: Dataspace pointer of selection to query
+        hsize_t *offset;        OUT: Linear offset of first element in selection
+ RETURNS
+    Non-negative on success, negative on failure
+ DESCRIPTION
+    Retrieves the linear offset (in "units" of elements) of the first element
+    selected within the dataspace.
+ GLOBAL VARIABLES
+ COMMENTS, BUGS, ASSUMPTIONS
+    Calling this function on a "none" selection returns fail.
+ EXAMPLES
+ REVISION LOG
+--------------------------------------------------------------------------*/
+herr_t
+H5S_hyper_offset(const H5S_t *space, hsize_t *offset)
+{
+    const hssize_t *sel_offset; /* Pointer to the selection's offset */
+    const hsize_t *dim_size;    /* Pointer to a dataspace's extent */
+    hsize_t accum;              /* Accumulator for dimension sizes */
+    int rank;                   /* Dataspace rank */
+    int i;                      /* index variable */
+    herr_t ret_value = SUCCEED; /* Return value */
+
+    FUNC_ENTER_NOAPI(H5S_hyper_offset, FAIL)
+
+    HDassert(space);
+    HDassert(offset);
+
+    /* Start at linear offset 0 */
+    *offset = 0;
+
+    /* Set up pointers to arrays of values */
+    rank = space->extent.rank;
+    sel_offset = space->select.offset;
+    dim_size = space->extent.size;
+
+    /* Check for a "regular" hyperslab selection */
+    if(space->select.sel_info.hslab->diminfo_valid) {
+        const H5S_hyper_dim_t *diminfo = space->select.sel_info.hslab->opt_diminfo; /* Local alias for diminfo */
+
+        /* Loop through starting coordinates, calculating the linear offset */
+        accum = 1;
+        for(i = (rank - 1); i >= 0; i--) {
+            hssize_t hyp_offset = (hssize_t)diminfo[i].start + sel_offset[i]; /* Hyperslab's offset in this dimension */
+
+            /* Check for offset moving selection out of the dataspace */
+            if(hyp_offset < 0 || (hsize_t)hyp_offset >= dim_size[i])
+                HGOTO_ERROR(H5E_DATASPACE, H5E_BADRANGE, FAIL, "offset moves selection out of bounds")
+
+            /* Add the hyperslab's offset in this dimension to the total linear offset */
+            *offset += hyp_offset * accum;
+
+            /* Increase the accumulator */
+            accum *= dim_size[i];
+        } /* end for */
+    } /* end if */
+    else {
+        const H5S_hyper_span_t *span;           /* Hyperslab span node */
+        hsize_t dim_accum[H5S_MAX_RANK];        /* Accumulators, for each dimension */
+
+        /* Calculate the accumulator for each dimension */
+        accum = 1;
+        for(i = (rank - 1); i >= 0; i--) {
+            /* Set the accumulator for this dimension */
+            dim_accum[i] = accum;
+
+            /* Increase the accumulator */
+            accum *= dim_size[i];
+        } /* end for */
+
+        /* Get information for the first span, in the slowest changing dimension */
+        span = space->select.sel_info.hslab->span_lst->head;
+
+        /* Work down the spans, computing the linear offset */
+        i = 0;
+        while(span) {
+            hssize_t hyp_offset = (hssize_t)span->low + sel_offset[i]; /* Hyperslab's offset in this dimension */
+
+            /* Check for offset moving selection out of the dataspace */
+            if(hyp_offset < 0 || (hsize_t)hyp_offset >= dim_size[i])
+                HGOTO_ERROR(H5E_DATASPACE, H5E_BADRANGE, FAIL, "offset moves selection out of bounds")
+
+            /* Add the hyperslab's offset in this dimension to the total linear offset */
+            *offset += hyp_offset * dim_accum[i];
+
+            /* Advance to first span in "down" dimension */
+            if(span->down) {
+                HDassert(span->down->head);
+                span = span->down->head;
+            } /* end if */
+            else
+                span = NULL;
+            i++;
+        } /* end while */
+    } /* end else */
+
+done:
+    FUNC_LEAVE_NOAPI(ret_value)
+}   /* H5S_hyper_offset() */
+
+
+/*--------------------------------------------------------------------------
+ NAME
     H5S_hyper_is_contiguous
  PURPOSE
     Check if a hyperslab selection is contiguous within the dataspace extent.
@@ -2727,12 +2837,10 @@ done:
 htri_t
 H5S_hyper_is_contiguous(const H5S_t *space)
 {
-    H5S_hyper_span_info_t *spans;   /* Hyperslab span info node */
-    H5S_hyper_span_t *span;         /* Hyperslab span node */
-    unsigned u;                     /* index variable */
     unsigned small_contiguous,      /* Flag for small contiguous block */
         large_contiguous;           /* Flag for large contiguous block */
-    htri_t ret_value=FALSE;         /* return value */
+    unsigned u;                     /* index variable */
+    htri_t ret_value = FALSE;       /* Return value */
 
     FUNC_ENTER_NOAPI_NOFUNC(H5S_hyper_is_contiguous);
 
@@ -2791,6 +2899,9 @@ H5S_hyper_is_contiguous(const H5S_t *space)
             ret_value=TRUE;
     } /* end if */
     else {
+        H5S_hyper_span_info_t *spans;   /* Hyperslab span info node */
+        H5S_hyper_span_t *span;         /* Hyperslab span node */
+
         /*
          * For a hyperslab to be contiguous, it must have only one block and
          * (either it's size must be the same as the dataspace extent's in all
diff --git a/src/H5Snone.c b/src/H5Snone.c
index 89a1875..88ab67f 100644
--- a/src/H5Snone.c
+++ b/src/H5Snone.c
@@ -43,6 +43,7 @@ static hssize_t H5S_none_serial_size(const H5S_t *space);
 static herr_t H5S_none_serialize(const H5S_t *space, uint8_t *buf);
 static herr_t H5S_none_deserialize(H5S_t *space, const uint8_t *buf);
 static herr_t H5S_none_bounds(const H5S_t *space, hsize_t *start, hsize_t *end);
+static herr_t H5S_none_offset(const H5S_t *space, hsize_t *off);
 static htri_t H5S_none_is_contiguous(const H5S_t *space);
 static htri_t H5S_none_is_single(const H5S_t *space);
 static htri_t H5S_none_is_regular(const H5S_t *space);
@@ -71,6 +72,7 @@ const H5S_select_class_t H5S_sel_none[1] = {{
     H5S_none_serialize,
     H5S_none_deserialize,
     H5S_none_bounds,
+    H5S_none_offset,
     H5S_none_is_contiguous,
     H5S_none_is_single,
     H5S_none_is_regular,
@@ -565,11 +567,43 @@ H5S_none_bounds(const H5S_t UNUSED *space, hsize_t UNUSED *start, hsize_t UNUSED
 
 /*--------------------------------------------------------------------------
  NAME
+    H5S_none_offset
+ PURPOSE
+    Gets the linear offset of the first element for the selection.
+ USAGE
+    herr_t H5S_none_offset(space, offset)
+        const H5S_t *space;     IN: Dataspace pointer of selection to query
+        hsize_t *offset;        OUT: Linear offset of first element in selection
+ RETURNS
+    Non-negative on success, negative on failure
+ DESCRIPTION
+    Retrieves the linear offset (in "units" of elements) of the first element
+    selected within the dataspace.
+ GLOBAL VARIABLES
+ COMMENTS, BUGS, ASSUMPTIONS
+    Calling this function on a "none" selection returns fail.
+ EXAMPLES
+ REVISION LOG
+--------------------------------------------------------------------------*/
+herr_t
+H5S_none_offset(const H5S_t *space, hsize_t *offset)
+{
+    FUNC_ENTER_NOAPI_NOFUNC(H5S_none_offset)
+
+    HDassert(space);
+    HDassert(offset);
+
+    FUNC_LEAVE_NOAPI(FAIL)
+}   /* H5S_none_offset() */
+
+
+/*--------------------------------------------------------------------------
+ NAME
     H5S_none_is_contiguous
  PURPOSE
     Check if a "none" selection is contiguous within the dataspace extent.
  USAGE
-    htri_t H5S_all_is_contiguous(space)
+    htri_t H5S_none_is_contiguous(space)
         H5S_t *space;           IN: Dataspace pointer to check
  RETURNS
     TRUE/FALSE/FAIL
@@ -767,7 +801,7 @@ done:
  PURPOSE
     Create a list of offsets & lengths for a selection
  USAGE
-    herr_t H5S_all_get_seq_list(space,flags,iter,maxseq,maxelem,nseq,nelem,off,len)
+    herr_t H5S_none_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
@@ -816,4 +850,5 @@ H5S_none_get_seq_list(const H5S_t UNUSED *space, unsigned UNUSED flags, H5S_sel_
     *nelem=0;
 
     FUNC_LEAVE_NOAPI(SUCCEED);
-} /* end H5S_all_get_seq_list() */
+} /* end H5S_none_get_seq_list() */
+
diff --git a/src/H5Spkg.h b/src/H5Spkg.h
index 71cc43b..3fe2ac3 100644
--- a/src/H5Spkg.h
+++ b/src/H5Spkg.h
@@ -133,8 +133,10 @@ typedef hssize_t (*H5S_sel_serial_size_func_t)(const H5S_t *space);
 typedef herr_t (*H5S_sel_serialize_func_t)(const H5S_t *space, uint8_t *buf);
 /* Method to store create selection from "serialized" form (a byte sequence suitable for storing on disk) */
 typedef herr_t (*H5S_sel_deserialize_func_t)(H5S_t *space, const uint8_t *buf);
-/* Method to determine to smallest n-D bounding box containing the current selection */
+/* Method to determine smallest n-D bounding box containing the current selection */
 typedef herr_t (*H5S_sel_bounds_func_t)(const H5S_t *space, hsize_t *start, hsize_t *end);
+/* Method to determine linear offset of initial element in selection within dataspace */
+typedef herr_t (*H5S_sel_offset_func_t)(const H5S_t *space, hsize_t *offset);
 /* Method to determine if current selection is contiguous */
 typedef htri_t (*H5S_sel_is_contiguous_func_t)(const H5S_t *space);
 /* Method to determine if current selection is a single block */
@@ -159,6 +161,7 @@ typedef struct {
     H5S_sel_serialize_func_t serialize;         /* Method to store current selection in "serialized" form (a byte sequence suitable for storing on disk) */
     H5S_sel_deserialize_func_t deserialize;     /* Method to store create selection from "serialized" form (a byte sequence suitable for storing on disk) */
     H5S_sel_bounds_func_t bounds;               /* Method to determine to smallest n-D bounding box containing the current selection */
+    H5S_sel_offset_func_t offset;               /* Method to determine linear offset of initial element in selection within dataspace */
     H5S_sel_is_contiguous_func_t is_contiguous; /* Method to determine if current selection is contiguous */
     H5S_sel_is_single_func_t is_single;         /* Method to determine if current selection is a single block */
     H5S_sel_is_regular_func_t is_regular;       /* Method to determine if current selection is "regular" */
diff --git a/src/H5Spoint.c b/src/H5Spoint.c
index eb37945..78c401c 100644
--- a/src/H5Spoint.c
+++ b/src/H5Spoint.c
@@ -44,6 +44,7 @@ static hssize_t H5S_point_serial_size(const H5S_t *space);
 static herr_t H5S_point_serialize(const H5S_t *space, uint8_t *buf);
 static herr_t H5S_point_deserialize(H5S_t *space, const uint8_t *buf);
 static herr_t H5S_point_bounds(const H5S_t *space, hsize_t *start, hsize_t *end);
+static herr_t H5S_point_offset(const H5S_t *space, hsize_t *off);
 static htri_t H5S_point_is_contiguous(const H5S_t *space);
 static htri_t H5S_point_is_single(const H5S_t *space);
 static htri_t H5S_point_is_regular(const H5S_t *space);
@@ -72,6 +73,7 @@ const H5S_select_class_t H5S_sel_point[1] = {{
     H5S_point_serialize,
     H5S_point_deserialize,
     H5S_point_bounds,
+    H5S_point_offset,
     H5S_point_is_contiguous,
     H5S_point_is_single,
     H5S_point_is_regular,
@@ -1038,48 +1040,114 @@ static herr_t
 H5S_point_bounds(const H5S_t *space, hsize_t *start, hsize_t *end)
 {
     H5S_pnt_node_t *node;       /* Point node */
-    int rank;                   /* Dataspace rank */
-    int i;                      /* index variable */
-    herr_t ret_value=SUCCEED;   /* Return value */
+    unsigned rank;              /* Dataspace rank */
+    unsigned u;                 /* index variable */
+    herr_t ret_value = SUCCEED;   /* Return value */
 
-    FUNC_ENTER_NOAPI_NOINIT(H5S_point_bounds);
+    FUNC_ENTER_NOAPI_NOINIT(H5S_point_bounds)
 
-    assert(space);
-    assert(start);
-    assert(end);
+    HDassert(space);
+    HDassert(start);
+    HDassert(end);
 
     /* Get the dataspace extent rank */
-    rank=space->extent.rank;
+    rank = space->extent.rank;
 
     /* Set the start and end arrays up */
-    for(i=0; i<rank; i++) {
-        start[i]=HSIZET_MAX;
-        end[i]=0;
+    for(u = 0; u < rank; u++) {
+        start[u] = HSIZET_MAX;
+        end[u] = 0;
     } /* end for */
 
     /* Iterate through the node, checking the bounds on each element */
-    node=space->select.sel_info.pnt_lst->head;
-    while(node!=NULL) {
-        for(i=0; i<rank; i++) {
+    node = space->select.sel_info.pnt_lst->head;
+    while(node != NULL) {
+        for(u = 0; u < rank; u++) {
             /* Check for offset moving selection negative */
-            if(((hssize_t)node->pnt[i]+space->select.offset[i])<0)
+            if(((hssize_t)node->pnt[u] + space->select.offset[u]) < 0)
                 HGOTO_ERROR(H5E_DATASPACE, H5E_BADRANGE, FAIL, "offset moves selection out of bounds")
 
-            if(start[i]>(node->pnt[i]+space->select.offset[i]))
-                start[i]=node->pnt[i]+space->select.offset[i];
-            if(end[i]<(node->pnt[i]+space->select.offset[i]))
-                end[i]=node->pnt[i]+space->select.offset[i];
+            if(start[u] > (node->pnt[u] + space->select.offset[u]))
+                start[u] = node->pnt[u] + space->select.offset[u];
+            if(end[u] < (node->pnt[u] + space->select.offset[u]))
+                end[u] = node->pnt[u] + space->select.offset[u];
         } /* end for */
-        node=node->next;
+        node = node->next;
       } /* end while */
 
 done:
-    FUNC_LEAVE_NOAPI(ret_value);
+    FUNC_LEAVE_NOAPI(ret_value)
 }   /* H5S_point_bounds() */
 
 
 /*--------------------------------------------------------------------------
  NAME
+    H5S_point_offset
+ PURPOSE
+    Gets the linear offset of the first element for the selection.
+ USAGE
+    herr_t H5S_point_offset(space, offset)
+        const H5S_t *space;     IN: Dataspace pointer of selection to query
+        hsize_t *offset;        OUT: Linear offset of first element in selection
+ RETURNS
+    Non-negative on success, negative on failure
+ DESCRIPTION
+    Retrieves the linear offset (in "units" of elements) of the first element
+    selected within the dataspace.
+ GLOBAL VARIABLES
+ COMMENTS, BUGS, ASSUMPTIONS
+    Calling this function on a "none" selection returns fail.
+ EXAMPLES
+ REVISION LOG
+--------------------------------------------------------------------------*/
+herr_t
+H5S_point_offset(const H5S_t *space, hsize_t *offset)
+{
+    const hsize_t *pnt;         /* Pointer to a selected point's coordinates */
+    const hssize_t *sel_offset; /* Pointer to the selection's offset */
+    const hsize_t *dim_size;    /* Pointer to a dataspace's extent */
+    hsize_t accum;              /* Accumulator for dimension sizes */
+    int rank;                   /* Dataspace rank */
+    int i;                      /* index variable */
+    herr_t ret_value = SUCCEED; /* Return value */
+
+    FUNC_ENTER_NOAPI(H5S_point_offset, FAIL)
+
+    HDassert(space);
+    HDassert(offset);
+
+    /* Start at linear offset 0 */
+    *offset = 0;
+
+    /* Set up pointers to arrays of values */
+    pnt = space->select.sel_info.pnt_lst->head->pnt;
+    sel_offset = space->select.offset;
+    dim_size = space->extent.size;
+
+    /* Loop through coordinates, calculating the linear offset */
+    rank = space->extent.rank;
+    accum = 1;
+    for(i = (rank - 1); i >= 0; i--) {
+        hssize_t pnt_offset = (hssize_t)pnt[i] + sel_offset[i]; /* Point's offset in this dimension */
+
+        /* Check for offset moving selection out of the dataspace */
+        if(pnt_offset < 0 || (hsize_t)pnt_offset >= dim_size[i])
+            HGOTO_ERROR(H5E_DATASPACE, H5E_BADRANGE, FAIL, "offset moves selection out of bounds")
+
+        /* Add the point's offset in this dimension to the total linear offset */
+        *offset += pnt_offset * accum;
+
+        /* Increase the accumulator */
+        accum *= dim_size[i];
+    } /* end for */
+
+done:
+    FUNC_LEAVE_NOAPI(ret_value)
+}   /* H5S_point_offset() */
+
+
+/*--------------------------------------------------------------------------
+ NAME
     H5S_point_is_contiguous
  PURPOSE
     Check if a point selection is contiguous within the dataspace extent.
diff --git a/src/H5Sprivate.h b/src/H5Sprivate.h
index ec48de9..8970890 100644
--- a/src/H5Sprivate.h
+++ b/src/H5Sprivate.h
@@ -152,6 +152,7 @@ typedef struct H5S_iostats_t {
 #define H5S_SELECT_SERIAL_SIZE(S)       ((*(S)->select.type->serial_size)(S))
 #define H5S_SELECT_SERIALIZE(S,BUF)     ((*(S)->select.type->serialize)(S,BUF))
 #define H5S_SELECT_BOUNDS(S,START,END)  ((*(S)->select.type->bounds)(S,START,END))
+#define H5S_SELECT_OFFSET(S, OFFSET)    ((*(S)->select.type->offset)(S, OFFSET))
 #define H5S_SELECT_IS_CONTIGUOUS(S)     ((*(S)->select.type->is_contiguous)(S))
 #define H5S_SELECT_IS_SINGLE(S)         ((*(S)->select.type->is_single)(S))
 #define H5S_SELECT_IS_REGULAR(S)        ((*(S)->select.type->is_regular)(S))
@@ -175,6 +176,7 @@ typedef struct H5S_iostats_t {
 #define H5S_SELECT_SERIAL_SIZE(S)       (H5S_select_serial_size(S))
 #define H5S_SELECT_SERIALIZE(S,BUF)     (H5S_select_serialize(S,BUF))
 #define H5S_SELECT_BOUNDS(S,START,END)  (H5S_get_select_bounds(S,START,END))
+#define H5S_SELECT_OFFSET(S, OFFSET)    (H5S_get_select_offset(S, OFFSET))
 #define H5S_SELECT_IS_CONTIGUOUS(S)     (H5S_select_is_contiguous(S))
 #define H5S_SELECT_IS_SINGLE(S)         (H5S_select_is_single(S))
 #define H5S_SELECT_IS_REGULAR(S)        (H5S_select_is_regular(S))
@@ -234,6 +236,7 @@ H5_DLL herr_t H5S_select_fill(const void *fill, size_t fill_size,
 H5_DLL htri_t H5S_select_valid(const H5S_t *space);
 H5_DLL hssize_t H5S_get_select_npoints(const H5S_t *space);
 H5_DLL herr_t H5S_get_select_bounds(const H5S_t *space, hsize_t *start, hsize_t *end);
+H5_DLL herr_t H5S_get_select_offset(const H5S_t *space, hsize_t *offset);
 H5_DLL herr_t H5S_select_offset(H5S_t *space, const hssize_t *offset);
 H5_DLL herr_t H5S_select_copy(H5S_t *dst, const H5S_t *src, hbool_t share_selection);
 H5_DLL htri_t H5S_select_shape_same(const H5S_t *space1, const H5S_t *space2);
diff --git a/src/H5Sselect.c b/src/H5Sselect.c
index 31fd05e..eba17a8 100644
--- a/src/H5Sselect.c
+++ b/src/H5Sselect.c
@@ -579,6 +579,46 @@ H5S_get_select_bounds(const H5S_t *space, hsize_t *start, hsize_t *end)
 
 /*--------------------------------------------------------------------------
  NAME
+    H5S_get_select_offset
+ PURPOSE
+    Gets the linear offset of the first element for the selection.
+ USAGE
+    herr_t H5S_get_select_offset(space, offset)
+        const H5S_t *space;     IN: Dataspace pointer of selection to query
+        hsize_t *offset;        OUT: Linear offset of first element in selection
+ RETURNS
+    Non-negative on success, negative on failure
+ DESCRIPTION
+    Retrieves the linear offset (in "units" of elements) of the first element
+    selected within the dataspace.
+ GLOBAL VARIABLES
+ COMMENTS, BUGS, ASSUMPTIONS
+        The offset calculation _does_ include the current offset of the
+    selection within the dataspace extent.
+
+        Calling this function on a "none" selection returns fail.
+ EXAMPLES
+ REVISION LOG
+--------------------------------------------------------------------------*/
+herr_t
+H5S_get_select_offset(const H5S_t *space, hsize_t *offset)
+{
+    herr_t ret_value;        /* return value */
+
+    FUNC_ENTER_NOAPI_NOFUNC(H5S_get_select_offset)
+
+    /* Check args */
+    HDassert(space);
+    HDassert(offset);
+
+    ret_value = (*space->select.type->offset)(space, offset);
+
+    FUNC_LEAVE_NOAPI(ret_value)
+}   /* H5S_get_select_offset() */
+
+
+/*--------------------------------------------------------------------------
+ NAME
     H5S_select_is_contiguous
  PURPOSE
     Determines if a selection is contiguous in the dataspace
diff --git a/test/dsets.c b/test/dsets.c
index 8719441..bf58018 100644
--- a/test/dsets.c
+++ b/test/dsets.c
@@ -6059,7 +6059,8 @@ test_random_chunks(void)
     for(i = 0; i < NPOINTS; i++)
         if(rbuf[i] != wbuf[i]){
             printf("    Line %d: Incorrect value, wbuf[%u]=%d, rbuf[%u]=%d\n",__LINE__,(unsigned)i,wbuf[i],(unsigned)i,rbuf[i]);
-                TEST_ERROR;
+            printf("             coord[%u] = {%lu, %lu}\n", (unsigned)i, (unsigned long)coord[i][0], (unsigned long)coord[i][1]);
+            TEST_ERROR;
         } /* end if */
 
     /* Close resources */