[svn-r2544] Optimized regular hyperslab I/O routines and data structures. On my benchmarks,

they are about 4-5 times faster than before.  We no longer generate "general"
hyperslab data structures for regular hyperslabs, the general data structures
are only generated when needed for irregular hyperslabs.

Still fixing a couple of nook-and-cranny functions to understand the new
information for the regular hyperslabs, so the tests aren't completely passing,
but I wanted to get this checked in for Elena's benchmarks.  I should have
more/all tests passing later today.

1 files changed, 1767 insertions, 293 deletions

diff --git a/src/H5Shyper.c b/src/H5Shyper.c
index c140e70..4348c82 100644
--- a/src/H5Shyper.c
+++ b/src/H5Shyper.c
@@ -60,8 +60,18 @@ static H5S_hyper_region_t * H5S_hyper_get_regions (size_t *num_regions,
                uintn rank, uintn dim, size_t bound_count,
                H5S_hyper_bound_t **lo_bounds, hssize_t *pos, hssize_t *offset);
 static size_t H5S_hyper_fread (intn dim, H5S_hyper_io_info_t *io_info);
+static size_t H5S_hyper_fread_opt (H5F_t *f, const struct H5O_layout_t *layout,
+		 const struct H5O_pline_t *pline, const struct H5O_fill_t *fill,
+		 const struct H5O_efl_t *efl, size_t elmt_size,
+		 const H5S_t *file_space, H5S_sel_iter_t *file_iter,
+		 size_t nelmts, hid_t dxpl_id, void *_buf/*out*/);
 static size_t H5S_hyper_fwrite (intn dim,
 				H5S_hyper_io_info_t *io_info);
+static size_t H5S_hyper_fwrite_opt (H5F_t *f, const struct H5O_layout_t *layout,
+		 const struct H5O_pline_t *pline, const struct H5O_fill_t *fill,
+		 const struct H5O_efl_t *efl, size_t elmt_size,
+		 const H5S_t *file_space, H5S_sel_iter_t *file_iter,
+		 size_t nelmts, hid_t dxpl_id, const void *_buf);
 static herr_t H5S_hyper_init (const struct H5O_layout_t *layout,
 			      const H5S_t *space, H5S_sel_iter_t *iter, size_t *min_elem_out);
 static size_t H5S_hyper_favail (const H5S_t *space, const H5S_sel_iter_t *iter,
@@ -80,10 +90,18 @@ static herr_t H5S_hyper_fscat (H5F_t *f, const struct H5O_layout_t *layout,
 			       const H5S_t *file_space,
 			       H5S_sel_iter_t *file_iter, size_t nelmts,
 			       hid_t dxpl_id, const void *buf);
+static size_t H5S_hyper_mread (intn dim, H5S_hyper_io_info_t *io_info);
+static herr_t H5S_hyper_mread_opt (const void *_buf, size_t elmt_size,
+		 const H5S_t *mem_space, H5S_sel_iter_t *mem_iter,
+		 size_t nelmts, void *_tconv_buf/*out*/);
 static size_t H5S_hyper_mgath (const void *_buf, size_t elmt_size,
 			       const H5S_t *mem_space,
 			       H5S_sel_iter_t *mem_iter, size_t nelmts,
 			       void *_tconv_buf/*out*/);
+static size_t H5S_hyper_mwrite (intn dim, H5S_hyper_io_info_t *io_info);
+static herr_t H5S_hyper_mwrite_opt (const void *_tconv_buf, size_t elmt_size,
+		 const H5S_t *mem_space, H5S_sel_iter_t *mem_iter,
+		 size_t nelmts, void *_buf/*out*/);
 static herr_t H5S_hyper_mscat (const void *_tconv_buf, size_t elmt_size,
 			       const H5S_t *mem_space,
 			       H5S_sel_iter_t *mem_iter, size_t nelmts,
@@ -808,6 +826,338 @@ H5S_hyper_fread (intn dim, H5S_hyper_io_info_t *io_info)
 
 
 /*-------------------------------------------------------------------------
+ * Function:	H5S_hyper_iter_next
+ *
+ * Purpose:	Moves a hyperslab iterator to the beginning of the next sequence
+ *      of elements to read.  Handles walking off the end in all dimensions.
+ *
+ * Return:	Success:	non-negative
+ *		Failure:	negative
+ *
+ * Programmer:	Quincey Koziol
+ *              Friday, September 8, 2000
+ *
+ * Modifications:
+ *
+ *-------------------------------------------------------------------------
+ */
+static int
+H5S_hyper_iter_next (const H5S_t *file_space, H5S_sel_iter_t *file_iter)
+{
+    hssize_t iter_offset[H5O_LAYOUT_NDIMS];
+    hssize_t iter_count[H5O_LAYOUT_NDIMS];
+    intn fast_dim;  /* Rank of the fastest changing dimension for the dataspace */
+    intn temp_dim;  /* Temporary rank holder */
+    intn i;         /* Counters */
+    uintn   	ndims;          /* Number of dimensions of dataset */
+    size_t num_read=0;          /* Number of elements read */
+
+    FUNC_ENTER (H5S_hyper_iter_next, FAIL);
+
+    /* Set some useful rank information */
+    fast_dim=file_space->extent.u.simple.rank-1;
+    ndims=file_space->extent.u.simple.rank;
+
+    /* Calculate the offset and block count for each dimension */
+    for(i=0; i<ndims; i++) {
+        iter_offset[i]=(file_iter->hyp.pos[i]-file_space->select.sel_info.hslab.diminfo[i].start)%file_space->select.sel_info.hslab.diminfo[i].stride;
+        iter_count[i]=(file_iter->hyp.pos[i]-file_space->select.sel_info.hslab.diminfo[i].start)/file_space->select.sel_info.hslab.diminfo[i].stride;
+    } /* end for */
+
+    /* Start with the fastest changing dimension */
+    temp_dim=fast_dim;
+    while(temp_dim>=0) {
+        if(temp_dim==fast_dim) {
+            /* Move to the next block in the current dimension */
+            iter_offset[temp_dim]=0;    /* reset the offset in the fastest dimension */
+            iter_count[temp_dim]++;
+
+            /* If this block is still in the range of blocks to output for the dimension, break out of loop */
+            if(iter_count[temp_dim]<file_space->select.sel_info.hslab.diminfo[temp_dim].count)
+                break;
+            else
+                iter_count[temp_dim]=0; /* reset back to the beginning of the line */
+        } /* end if */
+        else {
+            /* Move to the next row in the curent dimension */
+            iter_offset[temp_dim]++;
+
+            /* If this block is still in the range of blocks to output for the dimension, break out of loop */
+            if(iter_offset[temp_dim]<file_space->select.sel_info.hslab.diminfo[temp_dim].block)
+                break;
+            else {
+                /* Move to the next block in the current dimension */
+                iter_offset[temp_dim]=0;
+                iter_count[temp_dim]++;
+
+                /* If this block is still in the range of blocks to output for the dimension, break out of loop */
+                if(iter_count[temp_dim]<file_space->select.sel_info.hslab.diminfo[temp_dim].count)
+                    break;
+                else
+                    iter_count[temp_dim]=0; /* reset back to the beginning of the line */
+            } /* end else */
+        } /* end else */
+
+        /* Decrement dimension count */
+        temp_dim--;
+    } /* end while */
+
+    /* Translate current iter_offset and iter_count into iterator position */
+    for(i=0; i<ndims; i++)
+        file_iter->hyp.pos[i]=file_space->select.sel_info.hslab.diminfo[i].start+(file_space->select.sel_info.hslab.diminfo[i].stride*iter_count[i])+iter_offset[i];
+
+    FUNC_LEAVE (SUCCEED);
+} /* H5S_hyper_iter_next() */
+
+
+/*-------------------------------------------------------------------------
+ * Function:	H5S_hyper_fread_opt
+ *
+ * Purpose:	Performs an optimized gather from the file, based on a regular
+ *      hyperslab (i.e. one which was generated from just one call to
+ *      H5Sselect_hyperslab).
+ *
+ * Return:	Success:	Number of elements copied.
+ *		Failure:	0
+ *
+ * Programmer:	Quincey Koziol
+ *              Friday, September 8, 2000
+ *
+ * Modifications:
+ *
+ *-------------------------------------------------------------------------
+ */
+static size_t
+H5S_hyper_fread_opt (H5F_t *f, const struct H5O_layout_t *layout,
+		 const struct H5O_pline_t *pline,
+		 const struct H5O_fill_t *fill,
+		 const struct H5O_efl_t *efl, size_t elmt_size,
+		 const H5S_t *file_space, H5S_sel_iter_t *file_iter,
+		 size_t nelmts, hid_t dxpl_id, void *_buf/*out*/)
+{
+    hsize_t	hsize[H5O_LAYOUT_NDIMS];        /* Hyperslab size */
+    hssize_t zero[H5O_LAYOUT_NDIMS];		/*zero			*/
+    hssize_t offset[H5O_LAYOUT_NDIMS];      /* Offset on disk */
+    hsize_t	tmp_count[H5O_LAYOUT_NDIMS];    /* Temporary block count */
+    hsize_t	tmp_block[H5O_LAYOUT_NDIMS];    /* Temporary block offset */
+    uint8_t	*buf=(uint8_t *)_buf;   /* Alias for pointer arithmetic */
+    intn fast_dim;  /* Rank of the fastest changing dimension for the dataspace */
+    intn temp_dim;  /* Temporary rank holder */
+    intn i;         /* Counters */
+    uintn   	ndims;      /* Number of dimensions of dataset */
+    intn actual_read;       /* The actual number of elements to read in */
+    size_t num_read=0;      /* Number of elements read */
+
+    FUNC_ENTER (H5S_hyper_fread_opt, 0);
+
+#ifdef QAK
+printf("%s: Called!\n",FUNC);
+#endif /* QAK */
+    /* Check if this is the first element read in from the hyperslab */
+    if(file_iter->hyp.pos[0]==(-1)) {
+        for(i=0; i<file_space->extent.u.simple.rank; i++)
+            file_iter->hyp.pos[i]=file_space->select.sel_info.hslab.diminfo[i].start;
+    } /* end if */
+
+#ifdef QAK
+for(i=0; i<file_space->extent.u.simple.rank; i++)
+    printf("%s: file_file->hyp.pos[%d]=%d\n",FUNC,(int)i,(int)file_iter->hyp.pos[i]);
+#endif /* QAK */
+
+    /* Set the rank of the fastest changing dimension */
+    fast_dim=file_space->extent.u.simple.rank-1;
+
+    /* Set up the hyperslab and 'zero' arrays */
+    ndims=file_space->extent.u.simple.rank;
+    /* initialize hyperslab size and offset in memory buffer */
+    for(i=0; i<(int)(ndims+1); i++) {
+        hsize[i]=1;     /* hyperslab size is 1, except for last element */
+        zero[i]=0;      /* memory offset is 0 */
+    } /* end for */
+    hsize[ndims] = elmt_size;
+
+    /* Check if we stopped in the middle of a sequence of elements */
+    if((file_iter->hyp.pos[fast_dim]-file_space->select.sel_info.hslab.diminfo[fast_dim].start)%file_space->select.sel_info.hslab.diminfo[fast_dim].stride!=0) {
+        intn leftover;  /* The number of elements left over from the last sequence */
+
+#ifdef QAK
+printf("%s: Check 1.0\n",FUNC);
+#endif /* QAK */
+        /* Calculate the number of elements left in the sequence */
+        leftover=file_space->select.sel_info.hslab.diminfo[fast_dim].block-((file_iter->hyp.pos[fast_dim]-file_space->select.sel_info.hslab.diminfo[fast_dim].start)%file_space->select.sel_info.hslab.diminfo[fast_dim].stride);
+
+        /* Make certain that we don't read too many */
+        actual_read=MIN(leftover,nelmts);
+
+        /* Set the hyperslab size in the fastest changing dimension to read in */
+        hsize[fast_dim]=actual_read;
+
+        /* Copy the location of the point to get */
+        HDmemcpy(offset, file_iter->hyp.pos,ndims*sizeof(hssize_t));
+        offset[ndims] = 0;
+
+        /* Add in the selection offset */
+        for(i=0; i<ndims; i++)
+            offset[i] += file_space->select.offset[i];
+
+        /* Read in the rest of the sequence, if possible */
+        if (H5F_arr_read(f, dxpl_id, layout, pline, fill, efl, hsize,
+             hsize, zero, offset, buf/*out*/)<0) {
+            HRETURN_ERROR(H5E_DATASPACE, H5E_READERROR, 0, "read error");
+        }
+
+        /* Increment the offset of the buffer */
+        buf+=elmt_size*actual_read;
+
+        /* Increment the count read */
+        num_read+=actual_read;
+
+        /* Decrement the number of elements left in selection */
+        file_iter->hyp.elmt_left-=actual_read;
+
+        /* Advance the point iterator */
+        /* If we had enough buffer space to read in the rest of the sequence
+         * in the fastest changing dimension, move the iterator offset to
+         * the beginning of the next block to read.  Otherwise, just advance
+         * the iterator in the fastest changing dimension.
+         */
+        if(actual_read==leftover) {
+            /* Move iterator offset to beginning of next sequence in the fastest changing dimension */
+            H5S_hyper_iter_next(file_space,file_iter);
+        } /* end if */
+        else {
+            file_iter->hyp.pos[fast_dim]+=actual_read; /* whole sequence not read in, just advance fastest dimension offset */
+        } /* end if */
+    } /* end if */
+
+    /* Now that we've cleared the "remainder" of the previous fastest dimension
+     * sequence, we must be at the beginning of a sequence, so use the fancy
+     * algorithm to compute the offsets and run through as many as possible,
+     * until the buffer fills up.
+     */
+    if(num_read<nelmts) { /* Just in case the "remainder" aboce filled the buffer */
+#ifdef QAK
+printf("%s: Check 2.0\n",FUNC);
+#endif /* QAK */
+        /* Compute the arrays to perform I/O on */
+        /* Copy the location of the point to get */
+        HDmemcpy(offset, file_iter->hyp.pos,ndims*sizeof(hssize_t));
+        offset[ndims] = 0;
+
+        /* Add in the selection offset */
+        for(i=0; i<ndims; i++)
+            offset[i] += file_space->select.offset[i];
+
+        /* Compute the current "counts" for this location */
+        for(i=0; i<ndims; i++) {
+            tmp_count[i] = (file_iter->hyp.pos[i]-file_space->select.sel_info.hslab.diminfo[i].start)%file_space->select.sel_info.hslab.diminfo[i].stride;
+            tmp_block[i] = (file_iter->hyp.pos[i]-file_space->select.sel_info.hslab.diminfo[i].start)/file_space->select.sel_info.hslab.diminfo[i].stride;
+        } /* end for */
+
+        /* Set the number of elements to read each time */
+        actual_read=file_space->select.sel_info.hslab.diminfo[fast_dim].block;
+        hsize[fast_dim]=actual_read;
+#ifdef QAK
+printf("%s: actual_read=%d\n",FUNC,(int)actual_read);
+for(i=0; i<file_space->extent.u.simple.rank; i++)
+    printf("%s: diminfo: start[%d]=%d, stride[%d]=%d, block[%d]=%d, count[%d]=%d\n",FUNC,
+        (int)i,(int)file_space->select.sel_info.hslab.diminfo[i].start,
+        (int)i,(int)file_space->select.sel_info.hslab.diminfo[i].stride,
+        (int)i,(int)file_space->select.sel_info.hslab.diminfo[i].block,
+        (int)i,(int)file_space->select.sel_info.hslab.diminfo[i].count);
+#endif /* QAK */
+
+        /* Read in data until an entire sequence can't be read in any longer */
+        while(num_read<nelmts) {
+            /* Check if we are running out of room in the buffer */
+            if((actual_read+num_read)>nelmts) {
+                actual_read=nelmts-num_read;
+                hsize[fast_dim]=actual_read;
+            } /* end if */
+
+#ifdef QAK
+printf("%s: num_read=%d\n",FUNC,(int)num_read);
+for(i=0; i<file_space->extent.u.simple.rank; i++)
+    printf("%s: tmp_count[%d]=%d, offset[%d]=%d\n",FUNC,(int)i,(int)tmp_count[i],(int)i,(int)offset[i]);
+#endif /* QAK */
+
+            /* Read in the sequence, if possible */
+            if (H5F_arr_read(f, dxpl_id, layout, pline, fill, efl, hsize,
+                 hsize, zero, offset, buf/*out*/)<0) {
+                HRETURN_ERROR(H5E_DATASPACE, H5E_READERROR, 0, "read error");
+            }
+
+            /* Increment the offset of the buffer */
+            buf+=elmt_size*actual_read;
+
+            /* Increment the count read */
+            num_read+=actual_read;
+
+            /* Decrement the number of elements left in selection */
+            file_iter->hyp.elmt_left-=actual_read;
+
+            /* Increment the offset and count */
+            temp_dim=fast_dim;
+            while(temp_dim>=0) {
+                if(temp_dim==fast_dim) {
+                    /* Move to the next block in the current dimension */
+                    /* Check for partial block read! */
+                    if(actual_read<file_space->select.sel_info.hslab.diminfo[fast_dim].block) {
+                        offset[temp_dim]+=actual_read;
+                        break;
+                    } /* end if */
+                    else {
+                        offset[temp_dim]+=file_space->select.sel_info.hslab.diminfo[temp_dim].stride;    /* reset the offset in the fastest dimension */
+                        tmp_count[temp_dim]++;
+                    } /* end else */
+
+                    /* If this block is still in the range of blocks to output for the dimension, break out of loop */
+                    if(tmp_count[temp_dim]<file_space->select.sel_info.hslab.diminfo[temp_dim].count)
+                        break;
+                    else {
+                        tmp_count[temp_dim]=0; /* reset back to the beginning of the line */
+                        offset[temp_dim]=file_space->select.sel_info.hslab.diminfo[temp_dim].start+file_space->select.offset[temp_dim];
+                    } /* end else */
+                } /* end if */
+                else {
+                    /* 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]<file_space->select.sel_info.hslab.diminfo[temp_dim].block)
+                        break;
+                    else {
+                        /* Move to the next block in the current dimension */
+                        offset[temp_dim]+=(file_space->select.sel_info.hslab.diminfo[temp_dim].stride-file_space->select.sel_info.hslab.diminfo[temp_dim].block);
+                        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]<file_space->select.sel_info.hslab.diminfo[temp_dim].count)
+                            break;
+                        else {
+                            tmp_count[temp_dim]=0; /* reset back to the beginning of the line */
+                            tmp_block[temp_dim]=0;
+                            offset[temp_dim]=file_space->select.sel_info.hslab.diminfo[temp_dim].start+file_space->select.offset[temp_dim];
+                        }
+                    } /* end else */
+                } /* end else */
+
+                /* Decrement dimension count */
+                temp_dim--;
+            } /* end while */
+        } /* end while */
+
+        /* Update the iterator with the location we stopped */
+        HDmemcpy(file_iter->hyp.pos, offset, ndims*sizeof(hssize_t));
+    } /* end if */
+
+    FUNC_LEAVE (num_read);
+} /* H5S_hyper_fread_opt() */
+
+
+/*-------------------------------------------------------------------------
  * Function:	H5S_hyper_fgath
  *
  * Purpose:	Gathers data points from file F and accumulates them in the
@@ -859,31 +1209,39 @@ H5S_hyper_fgath (H5F_t *f, const struct H5O_layout_t *layout,
     printf("%s: check 1.0\n", FUNC);
 #endif /* QAK */
 
-    /* Initialize parameter block for recursive calls */
-    io_info.f=f;
-    io_info.layout=layout;
-    io_info.pline=pline;
-    io_info.fill=fill;
-    io_info.efl=efl;
-    io_info.elmt_size=elmt_size;
-    io_info.space=file_space;
-    io_info.iter=file_iter;
-    io_info.nelmts=nelmts;
-    io_info.dxpl_id = dxpl_id;
-    io_info.src=NULL;
-    io_info.dst=_buf;
-
-    /* Set the hyperslab size to copy */
-    io_info.hsize[0]=1;
-    H5V_array_fill(io_info.hsize,io_info.hsize,sizeof(io_info.hsize[0]),file_space->extent.u.simple.rank);
-    io_info.hsize[file_space->extent.u.simple.rank]=elmt_size;
-
-    /* Recursively input the hyperslabs currently defined */
-    /* starting with the slowest changing dimension */
-    num_read=H5S_hyper_fread(-1,&io_info);
+    /* Check for the special case of just one H5Sselect_hyperslab call made */
+    if(file_space->select.sel_info.hslab.diminfo!=NULL) {
+        /* Use optimized call to read in regular hyperslab */
+        num_read=H5S_hyper_fread_opt(f,layout,pline,fill,efl,elmt_size,file_space,file_iter,nelmts,dxpl_id,_buf);
+    } /* end if */
+    /* Perform generic hyperslab operation */
+    else {
+        /* Initialize parameter block for recursive calls */
+        io_info.f=f;
+        io_info.layout=layout;
+        io_info.pline=pline;
+        io_info.fill=fill;
+        io_info.efl=efl;
+        io_info.elmt_size=elmt_size;
+        io_info.space=file_space;
+        io_info.iter=file_iter;
+        io_info.nelmts=nelmts;
+        io_info.dxpl_id = dxpl_id;
+        io_info.src=NULL;
+        io_info.dst=_buf;
+
+        /* Set the hyperslab size to copy */
+        io_info.hsize[0]=1;
+        H5V_array_fill(io_info.hsize,io_info.hsize,sizeof(io_info.hsize[0]),file_space->extent.u.simple.rank);
+        io_info.hsize[file_space->extent.u.simple.rank]=elmt_size;
+
+        /* Recursively input the hyperslabs currently defined */
+        /* starting with the slowest changing dimension */
+        num_read=H5S_hyper_fread(-1,&io_info);
 #ifdef QAK
-    printf("%s: check 5.0, num_read=%d\n",FUNC,(int)num_read);
+        printf("%s: check 5.0, num_read=%d\n",FUNC,(int)num_read);
 #endif /* QAK */
+    } /* end else */
 
     FUNC_LEAVE (ret_value==SUCCEED ? num_read : 0);
 } /* H5S_hyper_fgath() */
@@ -1053,6 +1411,253 @@ H5S_hyper_fwrite (intn dim, H5S_hyper_io_info_t *io_info)
 
 
 /*-------------------------------------------------------------------------
+ * Function:	H5S_hyper_fwrite_opt
+ *
+ * Purpose:	Performs an optimized scatter to the file, based on a regular
+ *      hyperslab (i.e. one which was generated from just one call to
+ *      H5Sselect_hyperslab).
+ *
+ * Return:	Success:	Number of elements copied.
+ *		Failure:	0
+ *
+ * Programmer:	Quincey Koziol
+ *              Tuesday, September 12, 2000
+ *
+ * Modifications:
+ *
+ *-------------------------------------------------------------------------
+ */
+static size_t
+H5S_hyper_fwrite_opt (H5F_t *f, const struct H5O_layout_t *layout,
+		 const struct H5O_pline_t *pline,
+		 const struct H5O_fill_t *fill,
+		 const struct H5O_efl_t *efl, size_t elmt_size,
+		 const H5S_t *file_space, H5S_sel_iter_t *file_iter,
+		 size_t nelmts, hid_t dxpl_id, const void *_buf)
+{
+    hsize_t	hsize[H5O_LAYOUT_NDIMS];        /* Hyperslab size */
+    hssize_t zero[H5O_LAYOUT_NDIMS];		/*zero			*/
+    hssize_t offset[H5O_LAYOUT_NDIMS];      /* Offset on disk */
+    hsize_t	tmp_count[H5O_LAYOUT_NDIMS];    /* Temporary block count */
+    hsize_t	tmp_block[H5O_LAYOUT_NDIMS];    /* Temporary block offset */
+    const uint8_t	*buf=(const uint8_t *)_buf;   /* Alias for pointer arithmetic */
+    intn fast_dim;  /* Rank of the fastest changing dimension for the dataspace */
+    intn temp_dim;  /* Temporary rank holder */
+    intn i;         /* Counters */
+    uintn   	ndims;      /* Number of dimensions of dataset */
+    intn actual_write;       /* The actual number of elements to read in */
+    size_t num_write=0;      /* Number of elements read */
+
+    FUNC_ENTER (H5S_hyper_fwrite_opt, 0);
+
+#ifdef QAK
+printf("%s: Called!\n",FUNC);
+#endif /* QAK */
+    /* Check if this is the first element read in from the hyperslab */
+    if(file_iter->hyp.pos[0]==(-1)) {
+        for(i=0; i<file_space->extent.u.simple.rank; i++)
+            file_iter->hyp.pos[i]=file_space->select.sel_info.hslab.diminfo[i].start;
+    } /* end if */
+
+#ifdef QAK
+for(i=0; i<file_space->extent.u.simple.rank; i++)
+    printf("%s: file_file->hyp.pos[%d]=%d\n",FUNC,(int)i,(int)file_iter->hyp.pos[i]);
+#endif /* QAK */
+
+    /* Set the rank of the fastest changing dimension */
+    fast_dim=file_space->extent.u.simple.rank-1;
+
+    /* Set up the hyperslab and 'zero' arrays */
+    ndims=file_space->extent.u.simple.rank;
+    /* initialize hyperslab size and offset in memory buffer */
+    for(i=0; i<(int)(ndims+1); i++) {
+        hsize[i]=1;     /* hyperslab size is 1, except for last element */
+        zero[i]=0;      /* memory offset is 0 */
+    } /* end for */
+    hsize[ndims] = elmt_size;
+
+    /* Check if we stopped in the middle of a sequence of elements */
+    if((file_iter->hyp.pos[fast_dim]-file_space->select.sel_info.hslab.diminfo[fast_dim].start)%file_space->select.sel_info.hslab.diminfo[fast_dim].stride!=0) {
+        intn leftover;  /* The number of elements left over from the last sequence */
+
+#ifdef QAK
+printf("%s: Check 1.0\n",FUNC);
+#endif /* QAK */
+        /* Calculate the number of elements left in the sequence */
+        leftover=file_space->select.sel_info.hslab.diminfo[fast_dim].block-((file_iter->hyp.pos[fast_dim]-file_space->select.sel_info.hslab.diminfo[fast_dim].start)%file_space->select.sel_info.hslab.diminfo[fast_dim].stride);
+
+        /* Make certain that we don't write too many */
+        actual_write=MIN(leftover,nelmts);
+
+        /* Set the hyperslab size in the fastest changing dimension to write in */
+        hsize[fast_dim]=actual_write;
+
+        /* Copy the location of the point to get */
+        HDmemcpy(offset, file_iter->hyp.pos,ndims*sizeof(hssize_t));
+        offset[ndims] = 0;
+
+        /* Add in the selection offset */
+        for(i=0; i<ndims; i++)
+            offset[i] += file_space->select.offset[i];
+
+        /* Read in the rest of the sequence, if possible */
+        if (H5F_arr_write(f, dxpl_id, layout, pline, fill, efl, hsize,
+             hsize, zero, offset, buf)<0) {
+            HRETURN_ERROR(H5E_DATASPACE, H5E_READERROR, 0, "write error");
+        }
+
+        /* Increment the offset of the buffer */
+        buf+=elmt_size*actual_write;
+
+        /* Increment the count write */
+        num_write+=actual_write;
+
+        /* Decrement the number of elements left in selection */
+        file_iter->hyp.elmt_left-=actual_write;
+
+        /* Advance the point iterator */
+        /* If we had enough buffer space to write out the rest of the sequence
+         * in the fastest changing dimension, move the iterator offset to
+         * the beginning of the next block to write.  Otherwise, just advance
+         * the iterator in the fastest changing dimension.
+         */
+        if(actual_write==leftover) {
+            /* Move iterator offset to beginning of next sequence in the fastest changing dimension */
+            H5S_hyper_iter_next(file_space,file_iter);
+        } /* end if */
+        else {
+            file_iter->hyp.pos[fast_dim]+=actual_write; /* whole sequence not written out, just advance fastest dimension offset */
+        } /* end if */
+    } /* end if */
+
+    /* Now that we've cleared the "remainder" of the previous fastest dimension
+     * sequence, we must be at the beginning of a sequence, so use the fancy
+     * algorithm to compute the offsets and run through as many as possible,
+     * until the buffer fills up.
+     */
+    if(num_write<nelmts) { /* Just in case the "remainder" aboce filled the buffer */
+#ifdef QAK
+printf("%s: Check 2.0\n",FUNC);
+#endif /* QAK */
+        /* Compute the arrays to perform I/O on */
+        /* Copy the location of the point to get */
+        HDmemcpy(offset, file_iter->hyp.pos,ndims*sizeof(hssize_t));
+        offset[ndims] = 0;
+
+        /* Add in the selection offset */
+        for(i=0; i<ndims; i++)
+            offset[i] += file_space->select.offset[i];
+
+        /* Compute the current "counts" for this location */
+        for(i=0; i<ndims; i++) {
+            tmp_count[i] = (file_iter->hyp.pos[i]-file_space->select.sel_info.hslab.diminfo[i].start)%file_space->select.sel_info.hslab.diminfo[i].stride;
+            tmp_block[i] = (file_iter->hyp.pos[i]-file_space->select.sel_info.hslab.diminfo[i].start)/file_space->select.sel_info.hslab.diminfo[i].stride;
+        } /* end for */
+
+        /* Set the number of elements to write each time */
+        actual_write=file_space->select.sel_info.hslab.diminfo[fast_dim].block;
+        hsize[fast_dim]=actual_write;
+#ifdef QAK
+printf("%s: actual_write=%d\n",FUNC,(int)actual_write);
+for(i=0; i<file_space->extent.u.simple.rank; i++)
+    printf("%s: diminfo: start[%d]=%d, stride[%d]=%d, block[%d]=%d, count[%d]=%d\n",FUNC,
+        (int)i,(int)file_space->select.sel_info.hslab.diminfo[i].start,
+        (int)i,(int)file_space->select.sel_info.hslab.diminfo[i].stride,
+        (int)i,(int)file_space->select.sel_info.hslab.diminfo[i].block,
+        (int)i,(int)file_space->select.sel_info.hslab.diminfo[i].count);
+#endif /* QAK */
+
+        /* Read in data until an entire sequence can't be written out any longer */
+        while(num_write<nelmts) {
+            /* Check if we are running out of room in the buffer */
+            if((actual_write+num_write)>nelmts) {
+                actual_write=nelmts-num_write;
+                hsize[fast_dim]=actual_write;
+            } /* end if */
+
+#ifdef QAK
+printf("%s: num_write=%d\n",FUNC,(int)num_write);
+for(i=0; i<file_space->extent.u.simple.rank; i++)
+    printf("%s: tmp_count[%d]=%d, offset[%d]=%d\n",FUNC,(int)i,(int)tmp_count[i],(int)i,(int)offset[i]);
+#endif /* QAK */
+
+            /* Read in the sequence, if possible */
+            if (H5F_arr_write(f, dxpl_id, layout, pline, fill, efl, hsize,
+                 hsize, zero, offset, buf)<0) {
+                HRETURN_ERROR(H5E_DATASPACE, H5E_READERROR, 0, "write error");
+            }
+
+            /* Increment the offset of the buffer */
+            buf+=elmt_size*actual_write;
+
+            /* Increment the count write */
+            num_write+=actual_write;
+
+            /* Decrement the number of elements left in selection */
+            file_iter->hyp.elmt_left-=actual_write;
+
+            /* Increment the offset and count */
+            temp_dim=fast_dim;
+            while(temp_dim>=0) {
+                if(temp_dim==fast_dim) {
+                    /* Move to the next block in the current dimension */
+                    /* Check for partial block write! */
+                    if(actual_write<file_space->select.sel_info.hslab.diminfo[fast_dim].block) {
+                        offset[temp_dim]+=actual_write;
+                        break;
+                    } /* end if */
+                    else {
+                        offset[temp_dim]+=file_space->select.sel_info.hslab.diminfo[temp_dim].stride;    /* reset the offset in the fastest dimension */
+                        tmp_count[temp_dim]++;
+                    } /* end else */
+
+                    /* If this block is still in the range of blocks to output for the dimension, break out of loop */
+                    if(tmp_count[temp_dim]<file_space->select.sel_info.hslab.diminfo[temp_dim].count)
+                        break;
+                    else {
+                        tmp_count[temp_dim]=0; /* reset back to the beginning of the line */
+                        offset[temp_dim]=file_space->select.sel_info.hslab.diminfo[temp_dim].start+file_space->select.offset[temp_dim];
+                    } /* end else */
+                } /* end if */
+                else {
+                    /* 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]<file_space->select.sel_info.hslab.diminfo[temp_dim].block)
+                        break;
+                    else {
+                        /* Move to the next block in the current dimension */
+                        offset[temp_dim]+=(file_space->select.sel_info.hslab.diminfo[temp_dim].stride-file_space->select.sel_info.hslab.diminfo[temp_dim].block);
+                        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]<file_space->select.sel_info.hslab.diminfo[temp_dim].count)
+                            break;
+                        else {
+                            tmp_count[temp_dim]=0; /* reset back to the beginning of the line */
+                            tmp_block[temp_dim]=0;
+                            offset[temp_dim]=file_space->select.sel_info.hslab.diminfo[temp_dim].start+file_space->select.offset[temp_dim];
+                        }
+                    } /* end else */
+                } /* end else */
+
+                /* Decrement dimension count */
+                temp_dim--;
+            } /* end while */
+        } /* end while */
+
+        /* Update the iterator with the location we stopped */
+        HDmemcpy(file_iter->hyp.pos, offset, ndims*sizeof(hssize_t));
+    } /* end if */
+
+    FUNC_LEAVE (num_write);
+} /* H5S_hyper_fwrite_opt() */
+
+
+/*-------------------------------------------------------------------------
  * Function:	H5S_hyper_fscat
  *
  * Purpose:	Scatters dataset elements from the type conversion buffer BUF
@@ -1099,31 +1704,38 @@ H5S_hyper_fscat (H5F_t *f, const struct H5O_layout_t *layout,
     printf("%s: check 1.0\n", FUNC);
 #endif /* QAK */
 
-    /* Initialize parameter block for recursive calls */
-    io_info.f=f;
-    io_info.layout=layout;
-    io_info.pline=pline;
-    io_info.fill=fill;
-    io_info.efl=efl;
-    io_info.elmt_size=elmt_size;
-    io_info.space=file_space;
-    io_info.iter=file_iter;
-    io_info.nelmts=nelmts;
-    io_info.dxpl_id = dxpl_id;
-    io_info.src=_buf;
-    io_info.dst=NULL;
-
-    /* Set the hyperslab size to copy */
-    io_info.hsize[0]=1;
-    H5V_array_fill(io_info.hsize,io_info.hsize,sizeof(io_info.hsize[0]),file_space->extent.u.simple.rank);
-    io_info.hsize[file_space->extent.u.simple.rank]=elmt_size;
-
-    /* Recursively input the hyperslabs currently defined */
-    /* starting with the slowest changing dimension */
-    num_written=H5S_hyper_fwrite(-1,&io_info);
+    /* Check for the special case of just one H5Sselect_hyperslab call made */
+    if(file_space->select.sel_info.hslab.diminfo!=NULL) {
+        /* Use optimized call to write out regular hyperslab */
+        num_written=H5S_hyper_fwrite_opt(f,layout,pline,fill,efl,elmt_size,file_space,file_iter,nelmts,dxpl_id,_buf);
+    }
+    else {
+        /* Initialize parameter block for recursive calls */
+        io_info.f=f;
+        io_info.layout=layout;
+        io_info.pline=pline;
+        io_info.fill=fill;
+        io_info.efl=efl;
+        io_info.elmt_size=elmt_size;
+        io_info.space=file_space;
+        io_info.iter=file_iter;
+        io_info.nelmts=nelmts;
+        io_info.dxpl_id = dxpl_id;
+        io_info.src=_buf;
+        io_info.dst=NULL;
+
+        /* Set the hyperslab size to copy */
+        io_info.hsize[0]=1;
+        H5V_array_fill(io_info.hsize,io_info.hsize,sizeof(io_info.hsize[0]),file_space->extent.u.simple.rank);
+        io_info.hsize[file_space->extent.u.simple.rank]=elmt_size;
+
+        /* Recursively input the hyperslabs currently defined */
+        /* starting with the slowest changing dimension */
+        num_written=H5S_hyper_fwrite(-1,&io_info);
 #ifdef QAK
-    printf("%s: check 2.0\n", FUNC);
+        printf("%s: check 2.0\n", FUNC);
 #endif /* QAK */
+    } /* end else */
 
     FUNC_LEAVE (ret_value==FAIL ? ret_value : (num_written >0) ? SUCCEED : FAIL);
 } /* H5S_hyper_fscat() */
@@ -1273,6 +1885,258 @@ H5S_hyper_mread (intn dim, H5S_hyper_io_info_t *io_info)
 
 
 /*-------------------------------------------------------------------------
+ * Function:	H5S_hyper_mread_opt
+ *
+ * Purpose:	Performs an optimized gather from a memory buffer, based on a
+ *      regular hyperslab (i.e. one which was generated from just one call to
+ *      H5Sselect_hyperslab).
+ *
+ * Return:	Success:	Number of elements copied.
+ *		Failure:	0
+ *
+ * Programmer:	Quincey Koziol
+ *              Tuesday, September 12, 2000
+ *
+ * Modifications:
+ *
+ *-------------------------------------------------------------------------
+ */
+static herr_t
+H5S_hyper_mread_opt (const void *_buf, size_t elmt_size,
+		 const H5S_t *mem_space, H5S_sel_iter_t *mem_iter,
+		 size_t nelmts, void *_tconv_buf/*out*/)
+{
+    hsize_t	mem_size[H5O_LAYOUT_NDIMS];     /* Size of the source buffer */
+    hsize_t	hsize[H5O_LAYOUT_NDIMS];        /* Hyperslab size */
+    hssize_t zero[H5O_LAYOUT_NDIMS];		/*zero			*/
+    hssize_t offset[H5O_LAYOUT_NDIMS];      /* Offset on disk */
+    hsize_t	tmp_count[H5O_LAYOUT_NDIMS];    /* Temporary block count */
+    hsize_t	tmp_block[H5O_LAYOUT_NDIMS];    /* Temporary block offset */
+    const uint8_t	*src=(const uint8_t *)_buf;   /* Alias for pointer arithmetic */
+    uint8_t	*dst=(uint8_t *)_tconv_buf;   /* Alias for pointer arithmetic */
+    intn fast_dim;  /* Rank of the fastest changing dimension for the dataspace */
+    intn temp_dim;  /* Temporary rank holder */
+    intn i;         /* Counters */
+    uintn   	ndims;      /* Number of dimensions of dataset */
+    intn actual_read;       /* The actual number of elements to read in */
+    size_t num_read=0;      /* Number of elements read */
+
+    FUNC_ENTER (H5S_hyper_fread_opt, 0);
+
+#ifdef QAK
+printf("%s: Called!\n",FUNC);
+#endif /* QAK */
+    /* Check if this is the first element read in from the hyperslab */
+    if(mem_iter->hyp.pos[0]==(-1)) {
+        for(i=0; i<mem_space->extent.u.simple.rank; i++)
+            mem_iter->hyp.pos[i]=mem_space->select.sel_info.hslab.diminfo[i].start;
+    } /* end if */
+
+#ifdef QAK
+for(i=0; i<mem_space->extent.u.simple.rank; i++)
+    printf("%s: mem_file->hyp.pos[%d]=%d\n",FUNC,(int)i,(int)mem_iter->hyp.pos[i]);
+#endif /* QAK */
+
+    /* Set the rank of the fastest changing dimension */
+    fast_dim=mem_space->extent.u.simple.rank-1;
+
+    /* Set up the hyperslab and 'zero' arrays */
+    ndims=mem_space->extent.u.simple.rank;
+    /* initialize hyperslab size and offset in memory buffer */
+    for(i=0; i<(int)(ndims+1); i++) {
+        hsize[i]=1;     /* hyperslab size is 1, except for last element */
+        zero[i]=0;      /* memory offset is 0 */
+    } /* end for */
+    hsize[ndims] = elmt_size;
+
+    /* Set up the size of the memory space */
+    HDmemcpy(mem_size, mem_space->extent.u.simple.size,mem_space->extent.u.simple.rank*sizeof(hsize_t));
+    mem_size[mem_space->extent.u.simple.rank]=elmt_size;
+
+    /* Check if we stopped in the middle of a sequence of elements */
+    if((mem_iter->hyp.pos[fast_dim]-mem_space->select.sel_info.hslab.diminfo[fast_dim].start)%mem_space->select.sel_info.hslab.diminfo[fast_dim].stride!=0) {
+        intn leftover;  /* The number of elements left over from the last sequence */
+
+#ifdef QAK
+printf("%s: Check 1.0\n",FUNC);
+#endif /* QAK */
+        /* Calculate the number of elements left in the sequence */
+        leftover=mem_space->select.sel_info.hslab.diminfo[fast_dim].block-((mem_iter->hyp.pos[fast_dim]-mem_space->select.sel_info.hslab.diminfo[fast_dim].start)%mem_space->select.sel_info.hslab.diminfo[fast_dim].stride);
+
+        /* Make certain that we don't read too many */
+        actual_read=MIN(leftover,nelmts);
+
+        /* Set the hyperslab size in the fastest changing dimension to read in */
+        hsize[fast_dim]=actual_read;
+
+        /* Copy the location of the point to get */
+        HDmemcpy(offset, mem_iter->hyp.pos,ndims*sizeof(hssize_t));
+        offset[ndims] = 0;
+
+        /* Add in the selection offset */
+        for(i=0; i<ndims; i++)
+            offset[i] += mem_space->select.offset[i];
+
+        /* Scatter out the rest of the sequence, if possible */
+        if (H5V_hyper_copy (ndims+1, hsize,
+            hsize, zero, dst,
+            mem_size, offset, src)<0) {
+            HRETURN_ERROR (H5E_DATASPACE, H5E_READERROR, 0, "unable to gather data from memory");
+        }
+
+        /* Increment the offset of the buffer */
+        dst+=elmt_size*actual_read;
+
+        /* Increment the count read */
+        num_read+=actual_read;
+
+        /* Decrement the number of elements left in selection */
+        mem_iter->hyp.elmt_left-=actual_read;
+
+        /* Advance the point iterator */
+        /* If we had enough buffer space to read in the rest of the sequence
+         * in the fastest changing dimension, move the iterator offset to
+         * the beginning of the next block to read.  Otherwise, just advance
+         * the iterator in the fastest changing dimension.
+         */
+        if(actual_read==leftover) {
+            /* Move iterator offset to beginning of next sequence in the fastest changing dimension */
+            H5S_hyper_iter_next(mem_space,mem_iter);
+        } /* end if */
+        else {
+            mem_iter->hyp.pos[fast_dim]+=actual_read; /* whole sequence not read in, just advance fastest dimension offset */
+        } /* end if */
+    } /* end if */
+
+    /* Now that we've cleared the "remainder" of the previous fastest dimension
+     * sequence, we must be at the beginning of a sequence, so use the fancy
+     * algorithm to compute the offsets and run through as many as possible,
+     * until the buffer fills up.
+     */
+    if(num_read<nelmts) { /* Just in case the "remainder" aboce filled the buffer */
+#ifdef QAK
+printf("%s: Check 2.0\n",FUNC);
+#endif /* QAK */
+        /* Compute the arrays to perform I/O on */
+        /* Copy the location of the point to get */
+        HDmemcpy(offset, mem_iter->hyp.pos,ndims*sizeof(hssize_t));
+        offset[ndims] = 0;
+
+        /* Add in the selection offset */
+        for(i=0; i<ndims; i++)
+            offset[i] += mem_space->select.offset[i];
+
+        /* Compute the current "counts" for this location */
+        for(i=0; i<ndims; i++) {
+            tmp_count[i] = (mem_iter->hyp.pos[i]-mem_space->select.sel_info.hslab.diminfo[i].start)%mem_space->select.sel_info.hslab.diminfo[i].stride;
+            tmp_block[i] = (mem_iter->hyp.pos[i]-mem_space->select.sel_info.hslab.diminfo[i].start)/mem_space->select.sel_info.hslab.diminfo[i].stride;
+        } /* end for */
+
+        /* Set the number of elements to read each time */
+        actual_read=mem_space->select.sel_info.hslab.diminfo[fast_dim].block;
+        hsize[fast_dim]=actual_read;
+#ifdef QAK
+printf("%s: actual_read=%d\n",FUNC,(int)actual_read);
+for(i=0; i<file_space->extent.u.simple.rank; i++)
+    printf("%s: diminfo: start[%d]=%d, stride[%d]=%d, block[%d]=%d, count[%d]=%d\n",FUNC,
+        (int)i,(int)mem_space->select.sel_info.hslab.diminfo[i].start,
+        (int)i,(int)mem_space->select.sel_info.hslab.diminfo[i].stride,
+        (int)i,(int)mem_space->select.sel_info.hslab.diminfo[i].block,
+        (int)i,(int)mem_space->select.sel_info.hslab.diminfo[i].count);
+#endif /* QAK */
+
+        /* Read in data until an entire sequence can't be written out any longer */
+        while(num_read<nelmts) {
+            /* Check if we are running out of room in the buffer */
+            if((actual_read+num_read)>nelmts) {
+                actual_read=nelmts-num_read;
+                hsize[fast_dim]=actual_read;
+            } /* end if */
+
+#ifdef QAK
+printf("%s: num_read=%d\n",FUNC,(int)num_read);
+for(i=0; i<mem_space->extent.u.simple.rank; i++)
+    printf("%s: tmp_count[%d]=%d, offset[%d]=%d\n",FUNC,(int)i,(int)tmp_count[i],(int)i,(int)offset[i]);
+#endif /* QAK */
+
+            /* Scatter out the rest of the sequence, if possible */
+            if (H5V_hyper_copy (ndims+1, hsize,
+                hsize, zero, dst,
+                mem_size, offset, src)<0) {
+                HRETURN_ERROR (H5E_DATASPACE, H5E_READERROR, 0, "unable to gather data from memory");
+            }
+
+            /* Increment the offset of the buffer */
+            dst+=elmt_size*actual_read;
+
+            /* Increment the count read */
+            num_read+=actual_read;
+
+            /* Decrement the number of elements left in selection */
+            mem_iter->hyp.elmt_left-=actual_read;
+
+            /* Increment the offset and count */
+            temp_dim=fast_dim;
+            while(temp_dim>=0) {
+                if(temp_dim==fast_dim) {
+                    /* Move to the next block in the current dimension */
+                    /* Check for partial block read! */
+                    if(actual_read<mem_space->select.sel_info.hslab.diminfo[fast_dim].block) {
+                        offset[temp_dim]+=actual_read;
+                        break;
+                    } /* end if */
+                    else {
+                        offset[temp_dim]+=mem_space->select.sel_info.hslab.diminfo[temp_dim].stride;    /* reset the offset in the fastest dimension */
+                        tmp_count[temp_dim]++;
+                    } /* end else */
+
+                    /* If this block is still in the range of blocks to output for the dimension, break out of loop */
+                    if(tmp_count[temp_dim]<mem_space->select.sel_info.hslab.diminfo[temp_dim].count)
+                        break;
+                    else {
+                        tmp_count[temp_dim]=0; /* reset back to the beginning of the line */
+                        offset[temp_dim]=mem_space->select.sel_info.hslab.diminfo[temp_dim].start+mem_space->select.offset[temp_dim];
+                    } /* end else */
+                } /* end if */
+                else {
+                    /* 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]<mem_space->select.sel_info.hslab.diminfo[temp_dim].block)
+                        break;
+                    else {
+                        /* Move to the next block in the current dimension */
+                        offset[temp_dim]+=(mem_space->select.sel_info.hslab.diminfo[temp_dim].stride-mem_space->select.sel_info.hslab.diminfo[temp_dim].block);
+                        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]<mem_space->select.sel_info.hslab.diminfo[temp_dim].count)
+                            break;
+                        else {
+                            tmp_count[temp_dim]=0; /* reset back to the beginning of the line */
+                            tmp_block[temp_dim]=0;
+                            offset[temp_dim]=mem_space->select.sel_info.hslab.diminfo[temp_dim].start+mem_space->select.offset[temp_dim];
+                        }
+                    } /* end else */
+                } /* end else */
+
+                /* Decrement dimension count */
+                temp_dim--;
+            } /* end while */
+        } /* end while */
+
+        /* Update the iterator with the location we stopped */
+        HDmemcpy(mem_iter->hyp.pos, offset, ndims*sizeof(hssize_t));
+    } /* end if */
+
+    FUNC_LEAVE (num_read);
+} /* end H5S_hyper_mread_opt() */
+
+
+/*-------------------------------------------------------------------------
  * Function:	H5S_hyper_mgath
  *
  * Purpose:	Gathers dataset elements from application memory BUF and
@@ -1317,29 +2181,36 @@ H5S_hyper_mgath (const void *_buf, size_t elmt_size,
     assert (_buf);
     assert (_tconv_buf);
 
-    /* Initialize parameter block for recursive calls */
-    io_info.elmt_size=elmt_size;
-    io_info.space=mem_space;
-    io_info.iter=mem_iter;
-    io_info.nelmts=nelmts;
-    io_info.src=_buf;
-    io_info.dst=_tconv_buf;
-
-    /* Set up the size of the memory space */
-    HDmemcpy(io_info.mem_size, mem_space->extent.u.simple.size,mem_space->extent.u.simple.rank*sizeof(hsize_t));
-    io_info.mem_size[mem_space->extent.u.simple.rank]=elmt_size;
-
-    /* Set the hyperslab size to copy */
-    io_info.hsize[0]=1;
-    H5V_array_fill(io_info.hsize, io_info.hsize, sizeof(io_info.hsize[0]),mem_space->extent.u.simple.rank);
-    io_info.hsize[mem_space->extent.u.simple.rank]=elmt_size;
-
-    /* Recursively input the hyperslabs currently defined */
-    /* starting with the slowest changing dimension */
-    num_read=H5S_hyper_mread(-1,&io_info);
+    /* Check for the special case of just one H5Sselect_hyperslab call made */
+    if(mem_space->select.sel_info.hslab.diminfo!=NULL) {
+        /* Use optimized call to read in regular hyperslab */
+        num_read=H5S_hyper_mread_opt(_buf,elmt_size,mem_space,mem_iter,nelmts,_tconv_buf);
+    }
+    else {
+        /* Initialize parameter block for recursive calls */
+        io_info.elmt_size=elmt_size;
+        io_info.space=mem_space;
+        io_info.iter=mem_iter;
+        io_info.nelmts=nelmts;
+        io_info.src=_buf;
+        io_info.dst=_tconv_buf;
+
+        /* Set up the size of the memory space */
+        HDmemcpy(io_info.mem_size, mem_space->extent.u.simple.size,mem_space->extent.u.simple.rank*sizeof(hsize_t));
+        io_info.mem_size[mem_space->extent.u.simple.rank]=elmt_size;
+
+        /* Set the hyperslab size to copy */
+        io_info.hsize[0]=1;
+        H5V_array_fill(io_info.hsize, io_info.hsize, sizeof(io_info.hsize[0]),mem_space->extent.u.simple.rank);
+        io_info.hsize[mem_space->extent.u.simple.rank]=elmt_size;
+
+        /* Recursively input the hyperslabs currently defined */
+        /* starting with the slowest changing dimension */
+        num_read=H5S_hyper_mread(-1,&io_info);
 #ifdef QAK
-    printf("%s: check 5.0, num_read=%d\n",FUNC,(int)num_read);
+        printf("%s: check 5.0, num_read=%d\n",FUNC,(int)num_read);
 #endif /* QAK */
+    } /* end else */
 
     FUNC_LEAVE (num_read);
 }   /* H5S_hyper_mgath() */
@@ -1488,6 +2359,258 @@ H5S_hyper_mwrite (intn dim, H5S_hyper_io_info_t *io_info)
 
 
 /*-------------------------------------------------------------------------
+ * Function:	H5S_hyper_mwrite_opt
+ *
+ * Purpose:	Performs an optimized scatter to a memory buffer, based on a
+ *      regular hyperslab (i.e. one which was generated from just one call to
+ *      H5Sselect_hyperslab).
+ *
+ * Return:	Success:	Number of elements copied.
+ *		Failure:	0
+ *
+ * Programmer:	Quincey Koziol
+ *              Tuesday, September 12, 2000
+ *
+ * Modifications:
+ *
+ *-------------------------------------------------------------------------
+ */
+static herr_t
+H5S_hyper_mwrite_opt (const void *_tconv_buf, size_t elmt_size,
+		 const H5S_t *mem_space, H5S_sel_iter_t *mem_iter,
+		 size_t nelmts, void *_buf/*out*/)
+{
+    hsize_t	mem_size[H5O_LAYOUT_NDIMS];     /* Size of the source buffer */
+    hsize_t	hsize[H5O_LAYOUT_NDIMS];        /* Hyperslab size */
+    hssize_t zero[H5O_LAYOUT_NDIMS];		/*zero			*/
+    hssize_t offset[H5O_LAYOUT_NDIMS];      /* Offset on disk */
+    hsize_t	tmp_count[H5O_LAYOUT_NDIMS];    /* Temporary block count */
+    hsize_t	tmp_block[H5O_LAYOUT_NDIMS];    /* Temporary block offset */
+    const uint8_t	*src=(const uint8_t *)_tconv_buf;   /* Alias for pointer arithmetic */
+    uint8_t	*dst=(uint8_t *)_buf;   /* Alias for pointer arithmetic */
+    intn fast_dim;  /* Rank of the fastest changing dimension for the dataspace */
+    intn temp_dim;  /* Temporary rank holder */
+    intn i;         /* Counters */
+    uintn   	ndims;      /* Number of dimensions of dataset */
+    intn actual_write;       /* The actual number of elements to read in */
+    size_t num_write=0;      /* Number of elements read */
+
+    FUNC_ENTER (H5S_hyper_fwrite_opt, 0);
+
+#ifdef QAK
+printf("%s: Called!\n",FUNC);
+#endif /* QAK */
+    /* Check if this is the first element read in from the hyperslab */
+    if(mem_iter->hyp.pos[0]==(-1)) {
+        for(i=0; i<mem_space->extent.u.simple.rank; i++)
+            mem_iter->hyp.pos[i]=mem_space->select.sel_info.hslab.diminfo[i].start;
+    } /* end if */
+
+#ifdef QAK
+for(i=0; i<mem_space->extent.u.simple.rank; i++)
+    printf("%s: mem_file->hyp.pos[%d]=%d\n",FUNC,(int)i,(int)mem_iter->hyp.pos[i]);
+#endif /* QAK */
+
+    /* Set the rank of the fastest changing dimension */
+    fast_dim=mem_space->extent.u.simple.rank-1;
+
+    /* Set up the hyperslab and 'zero' arrays */
+    ndims=mem_space->extent.u.simple.rank;
+    /* initialize hyperslab size and offset in memory buffer */
+    for(i=0; i<(int)(ndims+1); i++) {
+        hsize[i]=1;     /* hyperslab size is 1, except for last element */
+        zero[i]=0;      /* memory offset is 0 */
+    } /* end for */
+    hsize[ndims] = elmt_size;
+
+    /* Set up the size of the memory space */
+    HDmemcpy(mem_size, mem_space->extent.u.simple.size,mem_space->extent.u.simple.rank*sizeof(hsize_t));
+    mem_size[mem_space->extent.u.simple.rank]=elmt_size;
+
+    /* Check if we stopped in the middle of a sequence of elements */
+    if((mem_iter->hyp.pos[fast_dim]-mem_space->select.sel_info.hslab.diminfo[fast_dim].start)%mem_space->select.sel_info.hslab.diminfo[fast_dim].stride!=0) {
+        intn leftover;  /* The number of elements left over from the last sequence */
+
+#ifdef QAK
+printf("%s: Check 1.0\n",FUNC);
+#endif /* QAK */
+        /* Calculate the number of elements left in the sequence */
+        leftover=mem_space->select.sel_info.hslab.diminfo[fast_dim].block-((mem_iter->hyp.pos[fast_dim]-mem_space->select.sel_info.hslab.diminfo[fast_dim].start)%mem_space->select.sel_info.hslab.diminfo[fast_dim].stride);
+
+        /* Make certain that we don't write too many */
+        actual_write=MIN(leftover,nelmts);
+
+        /* Set the hyperslab size in the fastest changing dimension to write in */
+        hsize[fast_dim]=actual_write;
+
+        /* Copy the location of the point to get */
+        HDmemcpy(offset, mem_iter->hyp.pos,ndims*sizeof(hssize_t));
+        offset[ndims] = 0;
+
+        /* Add in the selection offset */
+        for(i=0; i<ndims; i++)
+            offset[i] += mem_space->select.offset[i];
+
+        /* Scatter out the rest of the sequence, if possible */
+        if (H5V_hyper_copy (ndims+1, hsize,
+            mem_size, offset, dst,
+            hsize, zero, src)<0) {
+            HRETURN_ERROR (H5E_DATASPACE, H5E_READERROR, 0, "unable to gather data from memory");
+        }
+
+        /* Increment the offset of the buffer */
+        src+=elmt_size*actual_write;
+
+        /* Increment the count write */
+        num_write+=actual_write;
+
+        /* Decrement the number of elements left in selection */
+        mem_iter->hyp.elmt_left-=actual_write;
+
+        /* Advance the point iterator */
+        /* If we had enough buffer space to write out the rest of the sequence
+         * in the fastest changing dimension, move the iterator offset to
+         * the beginning of the next block to write.  Otherwise, just advance
+         * the iterator in the fastest changing dimension.
+         */
+        if(actual_write==leftover) {
+            /* Move iterator offset to beginning of next sequence in the fastest changing dimension */
+            H5S_hyper_iter_next(mem_space,mem_iter);
+        } /* end if */
+        else {
+            mem_iter->hyp.pos[fast_dim]+=actual_write; /* whole sequence not written out, just advance fastest dimension offset */
+        } /* end if */
+    } /* end if */
+
+    /* Now that we've cleared the "remainder" of the previous fastest dimension
+     * sequence, we must be at the beginning of a sequence, so use the fancy
+     * algorithm to compute the offsets and run through as many as possible,
+     * until the buffer fills up.
+     */
+    if(num_write<nelmts) { /* Just in case the "remainder" aboce filled the buffer */
+#ifdef QAK
+printf("%s: Check 2.0\n",FUNC);
+#endif /* QAK */
+        /* Compute the arrays to perform I/O on */
+        /* Copy the location of the point to get */
+        HDmemcpy(offset, mem_iter->hyp.pos,ndims*sizeof(hssize_t));
+        offset[ndims] = 0;
+
+        /* Add in the selection offset */
+        for(i=0; i<ndims; i++)
+            offset[i] += mem_space->select.offset[i];
+
+        /* Compute the current "counts" for this location */
+        for(i=0; i<ndims; i++) {
+            tmp_count[i] = (mem_iter->hyp.pos[i]-mem_space->select.sel_info.hslab.diminfo[i].start)%mem_space->select.sel_info.hslab.diminfo[i].stride;
+            tmp_block[i] = (mem_iter->hyp.pos[i]-mem_space->select.sel_info.hslab.diminfo[i].start)/mem_space->select.sel_info.hslab.diminfo[i].stride;
+        } /* end for */
+
+        /* Set the number of elements to write each time */
+        actual_write=mem_space->select.sel_info.hslab.diminfo[fast_dim].block;
+        hsize[fast_dim]=actual_write;
+#ifdef QAK
+printf("%s: actual_write=%d\n",FUNC,(int)actual_write);
+for(i=0; i<file_space->extent.u.simple.rank; i++)
+    printf("%s: diminfo: start[%d]=%d, stride[%d]=%d, block[%d]=%d, count[%d]=%d\n",FUNC,
+        (int)i,(int)mem_space->select.sel_info.hslab.diminfo[i].start,
+        (int)i,(int)mem_space->select.sel_info.hslab.diminfo[i].stride,
+        (int)i,(int)mem_space->select.sel_info.hslab.diminfo[i].block,
+        (int)i,(int)mem_space->select.sel_info.hslab.diminfo[i].count);
+#endif /* QAK */
+
+        /* Read in data until an entire sequence can't be written out any longer */
+        while(num_write<nelmts) {
+            /* Check if we are running out of room in the buffer */
+            if((actual_write+num_write)>nelmts) {
+                actual_write=nelmts-num_write;
+                hsize[fast_dim]=actual_write;
+            } /* end if */
+
+#ifdef QAK
+printf("%s: num_write=%d\n",FUNC,(int)num_write);
+for(i=0; i<mem_space->extent.u.simple.rank; i++)
+    printf("%s: tmp_count[%d]=%d, offset[%d]=%d\n",FUNC,(int)i,(int)tmp_count[i],(int)i,(int)offset[i]);
+#endif /* QAK */
+
+            /* Scatter out the rest of the sequence, if possible */
+            if (H5V_hyper_copy (ndims+1, hsize,
+                mem_size, offset, dst,
+                hsize, zero, src)<0) {
+                HRETURN_ERROR (H5E_DATASPACE, H5E_READERROR, 0, "unable to gather data from memory");
+            }
+
+            /* Increment the offset of the buffer */
+            src+=elmt_size*actual_write;
+
+            /* Increment the count write */
+            num_write+=actual_write;
+
+            /* Decrement the number of elements left in selection */
+            mem_iter->hyp.elmt_left-=actual_write;
+
+            /* Increment the offset and count */
+            temp_dim=fast_dim;
+            while(temp_dim>=0) {
+                if(temp_dim==fast_dim) {
+                    /* Move to the next block in the current dimension */
+                    /* Check for partial block write! */
+                    if(actual_write<mem_space->select.sel_info.hslab.diminfo[fast_dim].block) {
+                        offset[temp_dim]+=actual_write;
+                        break;
+                    } /* end if */
+                    else {
+                        offset[temp_dim]+=mem_space->select.sel_info.hslab.diminfo[temp_dim].stride;    /* reset the offset in the fastest dimension */
+                        tmp_count[temp_dim]++;
+                    } /* end else */
+
+                    /* If this block is still in the range of blocks to output for the dimension, break out of loop */
+                    if(tmp_count[temp_dim]<mem_space->select.sel_info.hslab.diminfo[temp_dim].count)
+                        break;
+                    else {
+                        tmp_count[temp_dim]=0; /* reset back to the beginning of the line */
+                        offset[temp_dim]=mem_space->select.sel_info.hslab.diminfo[temp_dim].start+mem_space->select.offset[temp_dim];
+                    } /* end else */
+                } /* end if */
+                else {
+                    /* 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]<mem_space->select.sel_info.hslab.diminfo[temp_dim].block)
+                        break;
+                    else {
+                        /* Move to the next block in the current dimension */
+                        offset[temp_dim]+=(mem_space->select.sel_info.hslab.diminfo[temp_dim].stride-mem_space->select.sel_info.hslab.diminfo[temp_dim].block);
+                        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]<mem_space->select.sel_info.hslab.diminfo[temp_dim].count)
+                            break;
+                        else {
+                            tmp_count[temp_dim]=0; /* reset back to the beginning of the line */
+                            tmp_block[temp_dim]=0;
+                            offset[temp_dim]=mem_space->select.sel_info.hslab.diminfo[temp_dim].start+mem_space->select.offset[temp_dim];
+                        }
+                    } /* end else */
+                } /* end else */
+
+                /* Decrement dimension count */
+                temp_dim--;
+            } /* end while */
+        } /* end while */
+
+        /* Update the iterator with the location we stopped */
+        HDmemcpy(mem_iter->hyp.pos, offset, ndims*sizeof(hssize_t));
+    } /* end if */
+
+    FUNC_LEAVE (num_write);
+} /* end H5S_hyper_mwrite_opt() */
+
+
+/*-------------------------------------------------------------------------
  * Function:	H5S_hyper_mscat
  *
  * Purpose:	Scatters NELMTS data points from the type conversion buffer
@@ -1509,8 +2632,8 @@ H5S_hyper_mscat (const void *_tconv_buf, size_t elmt_size,
 		 const H5S_t *mem_space, H5S_sel_iter_t *mem_iter,
 		 size_t nelmts, void *_buf/*out*/)
 {
-    H5S_hyper_io_info_t io_info;  /* Block of parameters to pass into recursive calls */
-    size_t  num_read;       /* number of elements read into buffer */
+    H5S_hyper_io_info_t io_info;    /* Block of parameters to pass into recursive calls */
+    size_t  num_written;            /* number of elements written into buffer */
 
     FUNC_ENTER (H5S_hyper_mscat, 0);
 
@@ -1522,34 +2645,41 @@ H5S_hyper_mscat (const void *_tconv_buf, size_t elmt_size,
     assert (_buf);
     assert (_tconv_buf);
 
-    /* Initialize parameter block for recursive calls */
-    io_info.elmt_size=elmt_size;
-    io_info.space=mem_space;
-    io_info.iter=mem_iter;
-    io_info.nelmts=nelmts;
-    io_info.src=_tconv_buf;
-    io_info.dst=_buf;
-
-    /* Set up the size of the memory space */
-    HDmemcpy(io_info.mem_size, mem_space->extent.u.simple.size,mem_space->extent.u.simple.rank*sizeof(hsize_t));
-    io_info.mem_size[mem_space->extent.u.simple.rank]=elmt_size;
-
-    /* Set the hyperslab size to copy */
-    io_info.hsize[0]=1;
-    H5V_array_fill(io_info.hsize, io_info.hsize, sizeof(io_info.hsize[0]), mem_space->extent.u.simple.rank);
-    io_info.hsize[mem_space->extent.u.simple.rank]=elmt_size;
-
-    /* Recursively input the hyperslabs currently defined */
-    /* starting with the slowest changing dimension */
+    /* Check for the special case of just one H5Sselect_hyperslab call made */
+    if(mem_space->select.sel_info.hslab.diminfo!=NULL) {
+        /* Use optimized call to write out regular hyperslab */
+        num_written=H5S_hyper_mwrite_opt(_tconv_buf,elmt_size,mem_space,mem_iter,nelmts,_buf);
+    }
+    else {
+        /* Initialize parameter block for recursive calls */
+        io_info.elmt_size=elmt_size;
+        io_info.space=mem_space;
+        io_info.iter=mem_iter;
+        io_info.nelmts=nelmts;
+        io_info.src=_tconv_buf;
+        io_info.dst=_buf;
+
+        /* Set up the size of the memory space */
+        HDmemcpy(io_info.mem_size, mem_space->extent.u.simple.size,mem_space->extent.u.simple.rank*sizeof(hsize_t));
+        io_info.mem_size[mem_space->extent.u.simple.rank]=elmt_size;
+
+        /* Set the hyperslab size to copy */
+        io_info.hsize[0]=1;
+        H5V_array_fill(io_info.hsize, io_info.hsize, sizeof(io_info.hsize[0]), mem_space->extent.u.simple.rank);
+        io_info.hsize[mem_space->extent.u.simple.rank]=elmt_size;
+
+        /* Recursively input the hyperslabs currently defined */
+        /* starting with the slowest changing dimension */
 #ifdef QAK
-    printf("%s: check 1.0\n",FUNC);
+        printf("%s: check 1.0\n",FUNC);
 #endif /* QAK */
-    num_read=H5S_hyper_mwrite(-1,&io_info);
+        num_written=H5S_hyper_mwrite(-1,&io_info);
 #ifdef QAK
-    printf("%s: check 2.0\n",FUNC);
+        printf("%s: check 2.0\n",FUNC);
 #endif /* QAK */
+    } /* end else */
 
-    FUNC_LEAVE (num_read>0 ? SUCCEED : FAIL);
+    FUNC_LEAVE (num_written>0 ? SUCCEED : FAIL);
 }   /* H5S_hyper_mscat() */
 
 
@@ -2380,30 +3510,36 @@ H5S_hyper_release (H5S_t *space)
     /* Reset the number of points selected */
     space->select.num_elem=0;
 
-    /* Release the per-dimension selection info */
-    if(space->select.sel_info.hslab.diminfo!=NULL)
+    /* Release the regular selection info */
+    if(space->select.sel_info.hslab.diminfo!=NULL) {
         H5FL_ARR_FREE(H5S_hyper_dim_t,space->select.sel_info.hslab.diminfo);
-    space->select.sel_info.hslab.diminfo = NULL;
+        space->select.sel_info.hslab.diminfo = NULL;
+    } /* end if */
 
-    /* Release hi and lo boundary information */
-    for(i=0; i<space->extent.u.simple.rank; i++) {
-        H5FL_ARR_FREE(H5S_hyper_bound_t,space->select.sel_info.hslab.hyper_lst->lo_bounds[i]);
-        space->select.sel_info.hslab.hyper_lst->lo_bounds[i] = NULL;
-    } /* end for */
-    H5FL_ARR_FREE(H5S_hyper_bound_ptr_t,space->select.sel_info.hslab.hyper_lst->lo_bounds);
-    space->select.sel_info.hslab.hyper_lst->lo_bounds = NULL;
+    /* Release irregular hyperslab information */
+    if(space->select.sel_info.hslab.hyper_lst!=NULL) {
+        /* Release hi and lo boundary information */
+        if(space->select.sel_info.hslab.hyper_lst->lo_bounds!=NULL) {
+            for(i=0; i<space->extent.u.simple.rank; i++) {
+                H5FL_ARR_FREE(H5S_hyper_bound_t,space->select.sel_info.hslab.hyper_lst->lo_bounds[i]);
+                space->select.sel_info.hslab.hyper_lst->lo_bounds[i] = NULL;
+            } /* end for */
+            H5FL_ARR_FREE(H5S_hyper_bound_ptr_t,space->select.sel_info.hslab.hyper_lst->lo_bounds);
+            space->select.sel_info.hslab.hyper_lst->lo_bounds = NULL;
+        } /* end if */
 
-    /* Release list of selected regions */
-    curr=space->select.sel_info.hslab.hyper_lst->head;
-    while(curr!=NULL) {
-        next=curr->next;
-        H5S_hyper_node_release(curr);
-        curr=next;
-    } /* end while */
+        /* Release list of selected regions */
+        curr=space->select.sel_info.hslab.hyper_lst->head;
+        while(curr!=NULL) {
+            next=curr->next;
+            H5S_hyper_node_release(curr);
+            curr=next;
+        } /* end while */
 
-    /* Release hyperslab selection node itself */
-    H5FL_FREE(H5S_hyper_list_t,space->select.sel_info.hslab.hyper_lst);
-    space->select.sel_info.hslab.hyper_lst=NULL;
+        /* Release hyperslab selection node itself */
+        H5FL_FREE(H5S_hyper_list_t,space->select.sel_info.hslab.hyper_lst);
+        space->select.sel_info.hslab.hyper_lst=NULL;
+    } /* end if */
 
 #ifdef QAK
     printf("%s: check 2.0\n",FUNC);
@@ -2522,7 +3658,7 @@ H5S_hyper_compare_bounds (const void *r1, const void *r2)
 herr_t
 H5S_hyper_copy (H5S_t *dst, const H5S_t *src)
 {
-    H5S_hyper_list_t *new_hyper;    /* New hyperslab selection */
+    H5S_hyper_list_t *new_hyper=NULL;    /* New hyperslab selection */
     H5S_hyper_node_t *curr, *new, *new_head;    /* Hyperslab information nodes */
     H5S_hyper_dim_t *new_diminfo=NULL;	/* New per-dimension info array[rank] */
     intn i;                     /* Counters */
@@ -2537,6 +3673,7 @@ H5S_hyper_copy (H5S_t *dst, const H5S_t *src)
 #ifdef QAK
     printf("%s: check 3.0\n", FUNC);
 #endif /* QAK */
+    /* Check if there is regular hyperslab information to copy */
     if(src->select.sel_info.hslab.diminfo!=NULL) {
         /* Create the per-dimension selection info */
         if((new_diminfo = H5FL_ARR_ALLOC(H5S_hyper_dim_t,src->extent.u.simple.rank,0))==NULL)
@@ -2552,87 +3689,91 @@ H5S_hyper_copy (H5S_t *dst, const H5S_t *src)
     } /* end if */
     dst->select.sel_info.hslab.diminfo = new_diminfo;
 
-    /* Create the new hyperslab information node */
-    if((new_hyper = H5FL_ALLOC(H5S_hyper_list_t,0))==NULL)
-        HGOTO_ERROR(H5E_RESOURCE, H5E_NOSPACE, FAIL,
-            "can't allocate point node");
+    /* Check if there is irregular hyperslab information to copy */
+    if(src->select.sel_info.hslab.hyper_lst!=NULL) {
+        /* Create the new hyperslab information node */
+        if((new_hyper = H5FL_ALLOC(H5S_hyper_list_t,0))==NULL)
+            HGOTO_ERROR(H5E_RESOURCE, H5E_NOSPACE, FAIL,
+                "can't allocate point node");
 
-    /* Copy the basic hyperslab selection information */
-    *new_hyper=*(src->select.sel_info.hslab.hyper_lst);
+        /* Copy the basic hyperslab selection information */
+        *new_hyper=*(src->select.sel_info.hslab.hyper_lst);
 
-    /* Attach the hyperslab information to the destination dataspace */
-    dst->select.sel_info.hslab.hyper_lst=new_hyper;
-    
 #ifdef QAK
-    printf("%s: check 4.0\n", FUNC);
+        printf("%s: check 4.0\n", FUNC);
 #endif /* QAK */
-    /* Allocate space for the low & high bound arrays */
-    if((new_hyper->lo_bounds = H5FL_ARR_ALLOC(H5S_hyper_bound_ptr_t,src->extent.u.simple.rank,0))==NULL)
-        HGOTO_ERROR(H5E_RESOURCE, H5E_NOSPACE, FAIL,
-            "can't allocate boundary node");
-    for(i=0; i<src->extent.u.simple.rank; i++) {
-        if((new_hyper->lo_bounds[i] = H5FL_ARR_ALLOC(H5S_hyper_bound_t,src->select.sel_info.hslab.hyper_lst->count,0))==NULL)
+        /* Allocate space for the low & high bound arrays */
+        if((new_hyper->lo_bounds = H5FL_ARR_ALLOC(H5S_hyper_bound_ptr_t,src->extent.u.simple.rank,0))==NULL)
             HGOTO_ERROR(H5E_RESOURCE, H5E_NOSPACE, FAIL,
-                "can't allocate boundary list");
-    } /* end for */
+                "can't allocate boundary node");
+        for(i=0; i<src->extent.u.simple.rank; i++) {
+            if((new_hyper->lo_bounds[i] = H5FL_ARR_ALLOC(H5S_hyper_bound_t,src->select.sel_info.hslab.hyper_lst->count,0))==NULL)
+                HGOTO_ERROR(H5E_RESOURCE, H5E_NOSPACE, FAIL,
+                    "can't allocate boundary list");
+        } /* end for */
 
 #ifdef QAK
-    printf("%s: check 5.0\n", FUNC);
+        printf("%s: check 5.0\n", FUNC);
 #endif /* QAK */
-    /* Copy the hyperslab selection nodes, adding them to the lo & hi bound arrays also */
-    curr=src->select.sel_info.hslab.hyper_lst->head;
-    new_head=NULL;
-    u=0;
-    while(curr!=NULL) {
+        /* Copy the hyperslab selection nodes, adding them to the lo & hi bound arrays also */
+        curr=src->select.sel_info.hslab.hyper_lst->head;
+        new_head=NULL;
+        u=0;
+        while(curr!=NULL) {
 #ifdef QAK
-    printf("%s: check 5.1\n", FUNC);
+        printf("%s: check 5.1\n", FUNC);
 #endif /* QAK */
-        /* Create each point */
-        if((new = H5FL_ALLOC(H5S_hyper_node_t,0))==NULL)
-            HGOTO_ERROR(H5E_RESOURCE, H5E_NOSPACE, FAIL,
-                "can't allocate point node");
-        HDmemcpy(new,curr,sizeof(H5S_hyper_node_t));    /* copy caching information */
-        if((new->start = H5FL_ARR_ALLOC(hsize_t,src->extent.u.simple.rank,0))==NULL)
-            HGOTO_ERROR(H5E_RESOURCE, H5E_NOSPACE, FAIL,
-                "can't allocate coordinate information");
-        if((new->end = H5FL_ARR_ALLOC(hsize_t,src->extent.u.simple.rank,0))==NULL)
-            HGOTO_ERROR(H5E_RESOURCE, H5E_NOSPACE, FAIL,
-                "can't allocate coordinate information");
-        HDmemcpy(new->start,curr->start,(src->extent.u.simple.rank*sizeof(hssize_t)));
-        HDmemcpy(new->end,curr->end,(src->extent.u.simple.rank*sizeof(hssize_t)));
-        new->next=NULL;
-
-        /* Insert into low & high bound arrays */
-        for(i=0; i<src->extent.u.simple.rank; i++) {
-            new_hyper->lo_bounds[i][u].bound=new->start[i];
-            new_hyper->lo_bounds[i][u].node=new;
-        } /* end for */
-        u++;    /* Increment the location of the next node in the boundary arrays */
+            /* Create each point */
+            if((new = H5FL_ALLOC(H5S_hyper_node_t,0))==NULL)
+                HGOTO_ERROR(H5E_RESOURCE, H5E_NOSPACE, FAIL,
+                    "can't allocate point node");
+            HDmemcpy(new,curr,sizeof(H5S_hyper_node_t));    /* copy caching information */
+            if((new->start = H5FL_ARR_ALLOC(hsize_t,src->extent.u.simple.rank,0))==NULL)
+                HGOTO_ERROR(H5E_RESOURCE, H5E_NOSPACE, FAIL,
+                    "can't allocate coordinate information");
+            if((new->end = H5FL_ARR_ALLOC(hsize_t,src->extent.u.simple.rank,0))==NULL)
+                HGOTO_ERROR(H5E_RESOURCE, H5E_NOSPACE, FAIL,
+                    "can't allocate coordinate information");
+            HDmemcpy(new->start,curr->start,(src->extent.u.simple.rank*sizeof(hssize_t)));
+            HDmemcpy(new->end,curr->end,(src->extent.u.simple.rank*sizeof(hssize_t)));
+            new->next=NULL;
+
+            /* Insert into low & high bound arrays */
+            for(i=0; i<src->extent.u.simple.rank; i++) {
+                new_hyper->lo_bounds[i][u].bound=new->start[i];
+                new_hyper->lo_bounds[i][u].node=new;
+            } /* end for */
+            u++;    /* Increment the location of the next node in the boundary arrays */
 
-        /* Keep the order the same when copying */
-        if(new_head==NULL)
-            new_head=new_hyper->head=new;
-        else {
-            new_head->next=new;
-            new_head=new;
-        } /* end else */
+            /* Keep the order the same when copying */
+            if(new_head==NULL)
+                new_head=new_hyper->head=new;
+            else {
+                new_head->next=new;
+                new_head=new;
+            } /* end else */
 
-        curr=curr->next;
-    } /* end while */
+            curr=curr->next;
+        } /* end while */
 #ifdef QAK
-    printf("%s: check 6.0\n", FUNC);
+        printf("%s: check 6.0\n", FUNC);
 #endif /* QAK */
 
-    /* Sort the boundary array */
-    for(i=0; i<src->extent.u.simple.rank; i++)
-        HDqsort(new_hyper->lo_bounds[i], new_hyper->count, sizeof(H5S_hyper_bound_t), H5S_hyper_compare_bounds);
+        /* Sort the boundary array */
+        for(i=0; i<src->extent.u.simple.rank; i++)
+            HDqsort(new_hyper->lo_bounds[i], new_hyper->count, sizeof(H5S_hyper_bound_t), H5S_hyper_compare_bounds);
 #ifdef QAK
-    printf("%s: check 7.0\n", FUNC);
+        printf("%s: check 7.0\n", FUNC);
 #endif /* QAK */
+    } /* end if */
+
+    /* Attach the hyperslab information to the destination dataspace */
+    dst->select.sel_info.hslab.hyper_lst=new_hyper;
 
 done:
     FUNC_LEAVE (ret_value);
 } /* end H5S_hyper_copy() */
+
 
 /*--------------------------------------------------------------------------
  NAME
@@ -2665,23 +3806,49 @@ H5S_hyper_select_valid (const H5S_t *space)
 
     assert(space);
 
-    /* Check each point to determine whether selection+offset is within extent */
-    curr=space->select.sel_info.hslab.hyper_lst->head;
-    while(curr!=NULL && ret_value==TRUE) {
+    /* Check for a "regular" hyperslab selection */
+    if(space->select.sel_info.hslab.diminfo != NULL) {
+        const H5S_hyper_dim_t *diminfo=space->select.sel_info.hslab.diminfo; /* local alias for diminfo */
+        hssize_t end;      /* The high bound of a region in a dimension */
+
         /* Check each dimension */
         for(i=0; i<space->extent.u.simple.rank; i++) {
-            /* Check if an offset has been defined */
-            /* Bounds check the selected point + offset against the extent */
-            if(((curr->start[i]+space->select.offset[i])>(hssize_t)space->extent.u.simple.size[i])
-                    || ((curr->start[i]+space->select.offset[i])<0)
-                || ((curr->end[i]+space->select.offset[i])>(hssize_t)space->extent.u.simple.size[i])
-                    || ((curr->end[i]+space->select.offset[i])<0)) {
+            /* Bounds check the start point in this dimension */
+            if((diminfo[i].start+space->select.offset[i])<0 ||
+                    (diminfo[i].start+space->select.offset[i])>=(hssize_t)space->extent.u.simple.size[i]) {
+                ret_value=FALSE;
+                break;
+            } /* end if */
+
+            /* Compute the largest location in this dimension */
+            end=diminfo[i].start+diminfo[i].stride*(diminfo[i].count-1)+(diminfo[i].block-1)+space->select.offset[i];
+
+            /* Bounds check the end point in this dimension */
+            if(end<0 || end>=(hssize_t)space->extent.u.simple.size[i]) {
                 ret_value=FALSE;
                 break;
             } /* end if */
         } /* end for */
+    } /* end if */
+    else {
+        /* Check each point to determine whether selection+offset is within extent */
+        curr=space->select.sel_info.hslab.hyper_lst->head;
+        while(curr!=NULL && ret_value==TRUE) {
+            /* Check each dimension */
+            for(i=0; i<space->extent.u.simple.rank; i++) {
+                /* Check if an offset has been defined */
+                /* Bounds check the selected point + offset against the extent */
+                if(((curr->start[i]+space->select.offset[i])>(hssize_t)space->extent.u.simple.size[i])
+                        || ((curr->start[i]+space->select.offset[i])<0)
+                    || ((curr->end[i]+space->select.offset[i])>(hssize_t)space->extent.u.simple.size[i])
+                        || ((curr->end[i]+space->select.offset[i])<0)) {
+                    ret_value=FALSE;
+                    break;
+                } /* end if */
+            } /* end for */
 
-        curr=curr->next;
+            curr=curr->next;
+        } /* end while */
     } /* end while */
 
     FUNC_LEAVE (ret_value);
@@ -2973,55 +4140,71 @@ H5S_hyper_select_contiguous(const H5S_t *space)
 
     assert(space);
 
-    /* If there is more than one hyperslab in the selection, they are not contiguous */
-    if(space->select.sel_info.hslab.hyper_lst->count>1)
-    	ret_value=FALSE;
-    else {	/* If there is one hyperslab, then it might be contiguous */
-	/* Get the dataspace extent rank */
-	rank=space->extent.u.simple.rank;
-
-	/* Get the hyperslab node */
-	node=space->select.sel_info.hslab.hyper_lst->head;
-
-	/*
-	 * For a hyperslab to be contiguous, it's size must be the same as the
-	 * dataspace extent's in all but the slowest changing dimension
-	 */
-	ret_value=TRUE;	/* assume true and reset if the dimensions don't match */
-	for(i=1; i<rank; i++) {
-		if(((node->end[i]-node->start[i])+1)!=(hssize_t)space->extent.u.simple.size[i]) {
-			ret_value=FALSE;
-			break;
-		} /* end if */
-	}
+    /* Check for a "regular" hyperslab selection */
+    if(space->select.sel_info.hslab.diminfo != NULL) {
+        /*
+         * For a regular hyperslab to be contiguous, it must have only one
+         * block (i.e. count==1 in all dimensions) and the block size must be
+         * the same as the dataspace extent's in all but the slowest changing
+         * dimension.
+         */
+        ret_value=TRUE;	/* assume true and reset if the dimensions don't match */
+        for(i=1; i<space->extent.u.simple.rank; i++) {
+            if(space->select.sel_info.hslab.diminfo[i].block>1 || space->select.sel_info.hslab.diminfo[i].block!=(hssize_t)space->extent.u.simple.size[i]) {
+                ret_value=FALSE;
+                break;
+            } /* end if */
+        } /* end for */
+    } /* end if */
+    else {
+        /* If there is more than one hyperslab in the selection, they are not contiguous */
+        if(space->select.sel_info.hslab.hyper_lst->count>1)
+            ret_value=FALSE;
+        else {	/* If there is one hyperslab, then it might be contiguous */
+            /* Get the dataspace extent rank */
+            rank=space->extent.u.simple.rank;
+
+            /* Get the hyperslab node */
+            node=space->select.sel_info.hslab.hyper_lst->head;
+
+            /*
+             * For a hyperslab to be contiguous, it's size must be the same as the
+             * dataspace extent's in all but the slowest changing dimension
+             */
+            ret_value=TRUE;	/* assume true and reset if the dimensions don't match */
+            for(i=1; i<rank; i++) {
+                if(((node->end[i]-node->start[i])+1)!=(hssize_t)space->extent.u.simple.size[i]) {
+                    ret_value=FALSE;
+                    break;
+                } /* end if */
+            } /* end for */
+        } /* end else */
     } /* end else */
     FUNC_LEAVE (ret_value);
 }   /* H5S_hyper_select_contiguous() */
 
 
 /*-------------------------------------------------------------------------
- * Function:	H5S_select_hyperslab
+ * Function:	H5S_generate_hyperlab
  *
- * Purpose:	Internal version of H5Sselect_hyperslab().
+ * Purpose:	Generate hyperslab information from H5S_select_hyperslab()
  *
  * Return:	Non-negative on success/Negative on failure
  *
- * Programmer:	Robb Matzke (split from HSselect_hyperslab()).
- *              Tuesday, August 25, 1998
+ * Programmer:	Quincey Koziol (split from HS_select_hyperslab()).
+ *              Tuesday, September 12, 2000
  *
  * Modifications:
  *
  *-------------------------------------------------------------------------
  */
-herr_t
-H5S_select_hyperslab (H5S_t *space, H5S_seloper_t op,
+static herr_t
+H5S_generate_hyperslab (H5S_t *space, H5S_seloper_t op,
 		      const hssize_t start[/*space_id*/],
 		      const hsize_t stride[/*space_id*/],
 		      const hsize_t count[/*space_id*/],
 		      const hsize_t block[/*space_id*/])
 {
-    hsize_t *_stride=NULL;        /* Stride array */
-    hsize_t *_block=NULL;        /* Block size array */
     hssize_t slab[H5O_LAYOUT_NDIMS]; /* Location of the block to add for strided selections */
     size_t slice[H5O_LAYOUT_NDIMS];	 /* Size of preceding dimension's slice */
     H5S_hyper_node_t *add=NULL, /* List of hyperslab nodes to add */
@@ -3030,54 +4213,18 @@ H5S_select_hyperslab (H5S_t *space, H5S_seloper_t op,
     uintn acc;                /* Accumulator for building slices */
     uintn contig;             /* whether selection is contiguous or not */
     int i,j;                  /* Counters */
-    H5S_hyper_dim_t *diminfo; /* per-dimension info for the selection */
     herr_t ret_value=FAIL;    /* return value */
 
-    FUNC_ENTER (H5S_select_hyperslab, FAIL);
+    FUNC_ENTER (H5S_generate_hyperslab, FAIL);
 
     /* Check args */
+    assert(block);
+    assert(stride);
     assert(space);
     assert(start);
     assert(count);
     assert(op>H5S_SELECT_NOOP && op<H5S_SELECT_INVALID);
     
-    /* Fill in the correct stride values */
-    if(stride==NULL) {
-        hssize_t fill=1;
-
-        /* Allocate temporary buffer */
-        if ((_stride=H5FL_ARR_ALLOC(hsize_t,space->extent.u.simple.rank,0))==NULL)
-                HGOTO_ERROR (H5E_RESOURCE, H5E_NOSPACE, FAIL,
-                     "memory allocation failed for stride buffer");
-        H5V_array_fill(_stride,&fill,sizeof(hssize_t),space->extent.u.simple.rank);
-        stride = _stride;
-    }
-
-    /* Fill in the correct block values */
-    if(block==NULL) {
-        hssize_t fill=1;
-
-        /* Allocate temporary buffer */
-        if ((_block=H5FL_ARR_ALLOC(hsize_t,space->extent.u.simple.rank,0))==NULL)
-                HGOTO_ERROR (H5E_RESOURCE, H5E_NOSPACE, FAIL,
-                     "memory allocation failed for stride buffer");
-        H5V_array_fill(_block,&fill,sizeof(hssize_t),space->extent.u.simple.rank);
-        block = _block;
-    }
-
-    /*
-     * Check for overlapping hyperslab blocks in new selection (remove when
-     *  real block-merging algorithm is in place? -QAK).
-     */
-    if(op==H5S_SELECT_SET && block!=NULL) {
-        for(i=0; i<space->extent.u.simple.rank; i++) {
-            if(stride[i]<block[i]) {
-                HGOTO_ERROR(H5E_ARGS, H5E_BADVALUE, FAIL,
-                    "hyperslab blocks overlap");
-            } /* end if */
-        } /* end for */
-    } /* end if */
-
     /* Determine if selection is contiguous */
     /* assume hyperslab is contiguous, until proven otherwise */
     contig=1;
@@ -3092,13 +4239,6 @@ H5S_select_hyperslab (H5S_t *space, H5S_seloper_t op,
 #ifdef QAK
     printf("%s: check 1.0, contig=%d, op=%s\n",FUNC,(int)contig,(op==H5S_SELECT_SET? "H5S_SELECT_SET" : (op==H5S_SELECT_OR ? "H5S_SELECT_OR" : "Unknown")));
 #endif /* QAK */
-    /* If we are setting a new selection, remove current selection first */
-    if(op==H5S_SELECT_SET) {
-        if(H5S_select_release(space)<0) {
-            HGOTO_ERROR(H5E_DATASPACE, H5E_CANTDELETE, FAIL,
-                "can't release hyperslab");
-        } /* end if */
-    } /* end if */
 
 #ifdef QAK
     printf("%s: check 2.0, rank=%d\n",FUNC,(int)space->extent.u.simple.rank);
@@ -3176,22 +4316,6 @@ H5S_select_hyperslab (H5S_t *space, H5S_seloper_t op,
                 H5S_hyper_clip(space,add,&uniq,NULL);
                 add=uniq;
             } /* end if */
-            else {
-#ifdef QAK
-    printf("%s: check 4.5.2\n",FUNC);
-#endif /* QAK */
-                /* Copy all the per-dimension selection info into the space descriptor */
-                if((diminfo = H5FL_ARR_ALLOC(H5S_hyper_dim_t,space->extent.u.simple.rank,0))==NULL) {
-                    HGOTO_ERROR(H5E_RESOURCE, H5E_NOSPACE, FAIL, "can't allocate per-dimension vector");
-                } /* end if */
-                for(i=0; i<space->extent.u.simple.rank; i++) {
-                    diminfo[i].start = start[i];
-                    diminfo[i].stride = stride[i];
-                    diminfo[i].count = count[i];
-                    diminfo[i].block = block[i];
-                } /* end for */
-                space->select.sel_info.hslab.diminfo = diminfo;
-            } /* end else */
 #ifdef QAK
     printf("%s: check 4.5.5\n",FUNC);
 #endif /* QAK */
@@ -3215,8 +4339,186 @@ H5S_select_hyperslab (H5S_t *space, H5S_seloper_t op,
     printf("%s: check 6.0\n",FUNC);
 #endif /* QAK */
 
+    /* Set return value */
+    ret_value=SUCCEED;
+
+done:
+    FUNC_LEAVE (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:	Robb Matzke (split from HSselect_hyperslab()).
+ *              Tuesday, August 25, 1998
+ *
+ * Modifications:
+ *
+ *-------------------------------------------------------------------------
+ */
+herr_t
+H5S_select_hyperslab (H5S_t *space, H5S_seloper_t op,
+		      const hssize_t start[/*space_id*/],
+		      const hsize_t stride[/*space_id*/],
+		      const hsize_t count[/*space_id*/],
+		      const hsize_t block[/*space_id*/])
+{
+    hsize_t *_stride=NULL;        /* Stride array */
+    hsize_t *_block=NULL;        /* Block size array */
+    hssize_t slab[H5O_LAYOUT_NDIMS]; /* Location of the block to add for strided selections */
+    size_t slice[H5O_LAYOUT_NDIMS];	 /* Size of preceding dimension's slice */
+    H5S_hyper_node_t *add=NULL, /* List of hyperslab nodes to add */
+        *uniq=NULL,         /* List of unique hyperslab nodes */
+        *tmp;               /* Temporary hyperslab node */
+    uintn acc;                /* Accumulator for building slices */
+    uintn contig;             /* whether selection is contiguous or not */
+    int i,j;                  /* Counters */
+    H5S_hyper_dim_t *diminfo; /* per-dimension info for the selection */
+    herr_t ret_value=FAIL;    /* return value */
+
+    FUNC_ENTER (H5S_select_hyperslab, FAIL);
+
+    /* Check args */
+    assert(space);
+    assert(start);
+    assert(count);
+    assert(op>H5S_SELECT_NOOP && op<H5S_SELECT_INVALID);
+    
+    /* Fill in the correct stride values */
+    if(stride==NULL) {
+        hssize_t fill=1;
+
+        /* Allocate temporary buffer */
+        if ((_stride=H5FL_ARR_ALLOC(hsize_t,space->extent.u.simple.rank,0))==NULL)
+                HGOTO_ERROR (H5E_RESOURCE, H5E_NOSPACE, FAIL,
+                     "memory allocation failed for stride buffer");
+        H5V_array_fill(_stride,&fill,sizeof(hssize_t),space->extent.u.simple.rank);
+        stride = _stride;
+    }
+
+    /* Fill in the correct block values */
+    if(block==NULL) {
+        hssize_t fill=1;
+
+        /* Allocate temporary buffer */
+        if ((_block=H5FL_ARR_ALLOC(hsize_t,space->extent.u.simple.rank,0))==NULL)
+                HGOTO_ERROR (H5E_RESOURCE, H5E_NOSPACE, FAIL,
+                     "memory allocation failed for stride buffer");
+        H5V_array_fill(_block,&fill,sizeof(hssize_t),space->extent.u.simple.rank);
+        block = _block;
+    }
+
+    /* Determine if selection is contiguous */
+    /* assume hyperslab is contiguous, until proven otherwise */
+    contig=1;
+    for(i=0; i<space->extent.u.simple.rank; i++) {
+        /* contiguous hyperslabs have the block size equal to the stride */
+        if(stride[i]!=block[i]) {
+            contig=0;   /* hyperslab isn't contiguous */
+            break;      /* no use looking further */
+        } /* end if */
+    } /* end for */
+
+#ifdef QAK
+    printf("%s: check 1.0, contig=%d, op=%s\n",FUNC,(int)contig,(op==H5S_SELECT_SET? "H5S_SELECT_SET" : (op==H5S_SELECT_OR ? "H5S_SELECT_OR" : "Unknown")));
+#endif /* QAK */
+    if(op==H5S_SELECT_SET) {
+        /*
+         * Check for overlapping hyperslab blocks in new selection
+         *  (remove when real block-merging algorithm is in place? -QAK).
+         */
+        for(i=0; i<space->extent.u.simple.rank; i++) {
+            if(count[i]>1 && stride[i]<block[i]) {
+                HGOTO_ERROR(H5E_ARGS, H5E_BADVALUE, FAIL,
+                    "hyperslab blocks overlap");
+            } /* end if */
+        } /* end for */
+
+        /* 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");
+        } /* end if */
+
+        /* Copy all the per-dimension selection info into the space descriptor */
+        if((diminfo = H5FL_ARR_ALLOC(H5S_hyper_dim_t,space->extent.u.simple.rank,0))==NULL) {
+            HGOTO_ERROR(H5E_RESOURCE, H5E_NOSPACE, FAIL, "can't allocate per-dimension vector");
+        } /* end if */
+        for(i=0; i<space->extent.u.simple.rank; i++) {
+            diminfo[i].start = start[i];
+            diminfo[i].stride = stride[i];
+            diminfo[i].count = count[i];
+            diminfo[i].block = block[i];
+        } /* end for */
+        space->select.sel_info.hslab.diminfo = diminfo;
+
+        /* Set the number of elements in the hyperslab selection */
+        for(space->select.num_elem=1,i=0; i<space->extent.u.simple.rank; i++)
+            space->select.num_elem*=block[i]*count[i];
+    } /* end if */
+    else if(op==H5S_SELECT_OR) {
+        switch(space->select.type) {
+            case H5S_SEL_ALL:
+                /* break out now, 'or'ing with an all selection leaves the all selection */
+                HGOTO_DONE(SUCCEED);
+                break;
+
+            case H5S_SEL_HYPERSLABS:
+                /* Is this the first 'or' operation? */
+                if(space->select.sel_info.hslab.diminfo != NULL) {
+                    /* yes, a "regular" hyperslab is selected currently */
+
+                    hssize_t tmp_start[H5O_LAYOUT_NDIMS];
+                    hsize_t tmp_stride[H5O_LAYOUT_NDIMS];
+                    hsize_t tmp_count[H5O_LAYOUT_NDIMS];
+                    hsize_t tmp_block[H5O_LAYOUT_NDIMS];
+
+                    /* Generate the hyperslab information for the regular hyperslab */
+
+                    /* Copy over the 'diminfo' information */
+                    for(i=0; i<space->extent.u.simple.rank; i++) {
+                        tmp_start[i]=space->select.sel_info.hslab.diminfo[i].start;
+                        tmp_stride[i]=space->select.sel_info.hslab.diminfo[i].stride;
+                        tmp_count[i]=space->select.sel_info.hslab.diminfo[i].count;
+                        tmp_block[i]=space->select.sel_info.hslab.diminfo[i].block;
+                    } /* end for */
+
+                    /* Reset the number of selection elements */
+                    space->select.num_elem=0;
+
+                    /* Build the hyperslab information */
+                    H5S_generate_hyperslab (space, H5S_SELECT_SET, tmp_start, tmp_stride, tmp_count, tmp_block);
+
+                    /* Remove the 'diminfo' information, since we're adding to it */
+                    H5FL_ARR_FREE(H5S_hyper_dim_t,space->select.sel_info.hslab.diminfo);
+                    space->select.sel_info.hslab.diminfo = NULL;
+
+                    /* Add in the new hyperslab information */
+                    H5S_generate_hyperslab (space, op, start, stride, count, block);
+                } /* end if */
+                else {
+                    /* nope, an "irregular" hyperslab is selected currently */
+                    /* Add in the new hyperslab information */
+                    H5S_generate_hyperslab (space, op, start, stride, count, block);
+                } /* end else */
+                break;
+
+            default:
+                HRETURN_ERROR(H5E_ARGS, H5E_UNSUPPORTED, FAIL, "invalid selection operation");
+        } /* end switch() */
+    } /* end if */
+    else {
+        HRETURN_ERROR(H5E_ARGS, H5E_UNSUPPORTED, FAIL, "invalid selection operation");
+    } /* end else */
+
     /* Set selection type */
     space->select.type=H5S_SEL_HYPERSLABS;
+
     ret_value=SUCCEED;
 
 done:
@@ -3225,7 +4527,7 @@ done:
     if(_block!=NULL)
         H5FL_ARR_FREE(hsize_t,_block);
     FUNC_LEAVE (ret_value);
-}
+}   /* end H5S_select_hyperslab() */
 
 
 /*--------------------------------------------------------------------------
@@ -3403,6 +4705,174 @@ H5S_hyper_select_iterate_mem (intn dim, H5S_hyper_iter_info_t *iter_info)
 
 /*--------------------------------------------------------------------------
  NAME
+    H5S_hyper_select_iterate_mem_opt
+ PURPOSE
+    Iterate over the data points in a regular hyperslab selection, calling a
+    user's function for each element.
+ USAGE
+    herr_t H5S_hyper_select_iterate_mem_opt(buf, type_id, space, op, operator_data)
+        H5S_sel_iter_t *iter;   IN/OUT: Selection iterator
+        void *buf;      IN/OUT: Buffer containing elements to iterate over
+        hid_t type_id;  IN: Datatype ID of BUF array.
+        H5S_t *space;   IN: Dataspace object containing selection to iterate over
+        H5D_operator_t op; IN: Function pointer to the routine to be
+                                called for each element in BUF iterated over.
+        void *op_data;  IN/OUT: Pointer to any user-defined data associated
+                                with the operation.
+ RETURNS
+    Returns the return value of the last operator if it was non-zero, or zero
+    if all elements were processed. Otherwise returns a negative value.
+ DESCRIPTION
+    Iterates over the selected elements in a memory buffer, calling the user's
+    callback function for each element.  The selection in the dataspace is
+    modified so that any elements already iterated over are removed from the
+    selection if the iteration is interrupted (by the H5D_operator_t function
+    returning non-zero) in the "middle" of the iteration and may be re-started
+    by the user where it left off.
+
+    NOTE: Until "subtracting" elements from a selection is implemented,
+        the selection is not modified.
+ GLOBAL VARIABLES
+ COMMENTS, BUGS, ASSUMPTIONS
+ EXAMPLES
+ REVISION LOG
+--------------------------------------------------------------------------*/
+static herr_t
+H5S_hyper_select_iterate_mem_opt(H5S_sel_iter_t *iter, void *buf, hid_t type_id, H5S_t *space, H5D_operator_t op,
+        void *op_data)
+{
+    H5S_hyper_dim_t *diminfo;               /* Alias for dataspace's diminfo information */
+    hsize_t tmp_count[H5O_LAYOUT_NDIMS];    /* Temporary hyperslab counts */
+    hsize_t tmp_block[H5O_LAYOUT_NDIMS];    /* Temporary hyperslab blocks */
+    hssize_t offset[H5O_LAYOUT_NDIMS];      /* Offset of element in dataspace */
+    hsize_t slab[H5O_LAYOUT_NDIMS];         /* Size of objects in buffer */
+    size_t elem_size;           /* Size of data element in buffer */
+    size_t temp_off;            /* Offset in a given dimension */
+    uint8_t *loc;               /* Current element location */
+    intn i;                     /* Counter */
+    intn fast_dim;      /* Rank of the fastest changing dimension for the dataspace */
+    intn temp_dim;      /* Temporary rank holder */
+    intn ndims;         /* Rank of the dataspace */
+    herr_t user_ret=0;          /* User's return value */
+
+    FUNC_ENTER (H5S_hyper_select_iterate_mem_opt, FAIL);
+
+    /* Set some convienence values */
+    ndims=space->extent.u.simple.rank;
+    fast_dim=ndims-1;
+    diminfo=space->select.sel_info.hslab.diminfo;
+
+    /* Get the data element size */
+    elem_size=H5Tget_size(type_id);
+
+    /* Elements in the fastest dimension are 'elem_size' */
+    slab[ndims-1]=elem_size;
+
+    /* If we have two or more dimensions, build the other dimension's element sizes */
+    if(ndims>=2) {
+        /* Build the table of next-dimension down 'element' sizes */
+        for(i=ndims-2; i>=0; i--)
+            slab[i]=slab[i+1]*space->extent.u.simple.size[i+1];
+    } /* end if */
+
+    /* Build the tables of count & block sizes as well as the initial offset */
+    for(i=0; i<ndims; i++) {
+        tmp_count[i]=diminfo[i].count;
+        tmp_block[i]=diminfo[i].block;
+        offset[i]=diminfo[i].start;
+    } /* end for */
+
+    /* Initialize the starting location */
+    for(loc=buf,i=0; i<ndims; i++)
+        loc+=diminfo[i].start*slab[i];
+
+    /* Go iterate over the hyperslabs */
+    while(user_ret==0) {
+        /* Iterate over the blocks in the fastest dimension */
+        while(tmp_count[fast_dim]>0 && user_ret==0) {
+
+            /* Iterate over the elements in the fastest dimension */
+            while(tmp_block[fast_dim]>0 && user_ret==0) {
+                user_ret=(*op)(loc,type_id,ndims,offset,op_data);
+
+                /* Increment the buffer location */
+                loc+=slab[fast_dim];
+
+                /* Increment the offset in the dataspace */
+                offset[fast_dim]++;
+
+                /* Decrement the sequence count */
+                tmp_block[fast_dim]--;
+            } /* end while */
+
+            /* Reset the sequence count */
+            tmp_block[fast_dim]=diminfo[fast_dim].block;
+
+            /* Move the location to the next sequence to start */
+            loc+=(diminfo[fast_dim].stride-diminfo[fast_dim].block)*slab[fast_dim];
+             
+            /* Move the offset to the next sequence to start */
+            offset[fast_dim]+=(diminfo[fast_dim].stride-diminfo[fast_dim].block);
+
+            /* Decrement the block count */
+            tmp_count[fast_dim]--;
+        } /* end while */
+
+        /* Work on other dimensions if necessary */
+        if(fast_dim>0 && user_ret==0) {
+            /* Reset the sequence and block counts */
+            tmp_block[fast_dim]=diminfo[fast_dim].block;
+            tmp_count[fast_dim]=diminfo[fast_dim].count;
+
+            /* Bubble up the decrement to the slower changing dimensions */
+            temp_dim=fast_dim-1;
+            while(temp_dim>=0) {
+                /* Decrement the sequence count in this dimension */
+                tmp_block[temp_dim]--;
+
+                /* Check if we are still in the sequence */
+                if(tmp_block[temp_dim]>0)
+                    break;
+
+                /* Reset the sequence count in this dimension */
+                tmp_block[temp_dim]=diminfo[temp_dim].block;
+
+                /* Decrement the block count */
+                tmp_count[temp_dim]--;
+
+                /* Check if we have more blocks left */
+                if(tmp_count[temp_dim]>0)
+                    break;
+
+                /* Check for getting out of iterator */
+                if(temp_dim==0)
+                    goto done; /* Yes, an evil goto.. :-) -QAK */
+
+                /* 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 buffer location & offset array */
+        for(loc=buf,i=0; i<ndims; i++) {
+            temp_off=diminfo[i].start
+                +diminfo[i].stride*(diminfo[i].count-tmp_count[i])
+                    +(diminfo[i].block-tmp_block[i]);
+            loc+=temp_off*slab[i];
+            offset[i]=temp_off;
+        } /* end for */
+    } /* end while */
+
+done:
+    FUNC_LEAVE (user_ret);
+} /* end H5S_hyper_select_iterate_mem_opt() */
+
+
+/*--------------------------------------------------------------------------
+ NAME
     H5S_hyper_select_iterate
  PURPOSE
     Iterate over a hyperslab selection, calling a user's function for each
@@ -3450,33 +4920,37 @@ H5S_hyper_select_iterate(void *buf, hid_t type_id, H5S_t *space, H5D_operator_t
     assert(op);
     assert(H5I_DATATYPE == H5I_get_type(type_id));
 
-    /* Initialize these before any errors can occur */
-    HDmemset(&iter,0,sizeof(H5S_sel_iter_t));
-
     /* Initialize the selection iterator */
     if (H5S_hyper_init(NULL, space, &iter, &min_elem_out)<0) {
         HGOTO_ERROR (H5E_DATASPACE, H5E_CANTINIT, FAIL,
 		     "unable to initialize selection information");
     } 
 
-    /* Initialize parameter block for recursive calls */
-    iter_info.dt=type_id;
-    iter_info.elem_size=H5Tget_size(type_id);
-    iter_info.space=space;
-    iter_info.iter=&iter;
-    iter_info.src=buf;
+    /* Check for the special case of just one H5Sselect_hyperslab call made */
+    if(space->select.sel_info.hslab.diminfo!=NULL) {
+        /* Use optimized call to iterate over regular hyperslab */
+        ret_value=H5S_hyper_select_iterate_mem_opt(&iter,buf,type_id,space,op,operator_data);
+    }
+    else {
+        /* Initialize parameter block for recursive calls */
+        iter_info.dt=type_id;
+        iter_info.elem_size=H5Tget_size(type_id);
+        iter_info.space=space;
+        iter_info.iter=&iter;
+        iter_info.src=buf;
 
-    /* Set up the size of the memory space */
-    HDmemcpy(iter_info.mem_size, space->extent.u.simple.size, space->extent.u.simple.rank*sizeof(hsize_t));
-    iter_info.mem_size[space->extent.u.simple.rank]=iter_info.elem_size;
+        /* Set up the size of the memory space */
+        HDmemcpy(iter_info.mem_size, space->extent.u.simple.size, space->extent.u.simple.rank*sizeof(hsize_t));
+        iter_info.mem_size[space->extent.u.simple.rank]=iter_info.elem_size;
 
-    /* Copy the location of the region in the file */
-    iter_info.op=op;
-    iter_info.op_data=operator_data;
+        /* Copy the location of the region in the file */
+        iter_info.op=op;
+        iter_info.op_data=operator_data;
 
-    /* Recursively input the hyperslabs currently defined */
-    /* starting with the slowest changing dimension */
-    ret_value=H5S_hyper_select_iterate_mem(-1,&iter_info);
+        /* Recursively input the hyperslabs currently defined */
+        /* starting with the slowest changing dimension */
+        ret_value=H5S_hyper_select_iterate_mem(-1,&iter_info);
+    } /* end else */
 
     /* Release selection iterator */
     H5S_sel_iter_release(space,&iter);