[svn-r335] Changes since 19980330

----------------------

./MANIFEST
./src/Makefile.in
./test/Makefile.in
        Added new files.

./config/linux
./src/H5HL.c
./src/H5HLprivate.h
./src/H5MF.c
./src/H5MFprivate.h
        Added `-DH5HL_DEBUG -DH5MF_DEBUG' to the debug list.

./html/H5.format.html
        Updated shared object message information.

./src/H5D.c
        Datasets can now share data types.

./src/H5F.c
        Updated a comment that referred to H5ACC_WRITE.

./src/H5HG.c
./src/H5HGprivate.h
        Moved a few things around.  Made debugging better so you can
        now give a collection address to ./src/debug and it shows some
        useful stuff.

./src/H5O.c
./src/H5Ocont.c
./src/H5Odtype.c
./src/H5Oefl.c
./src/H5Olayout.c
./src/H5Oname.c
./src/H5Onull.c
./src/H5Oprivate.h
./src/H5Osdspace.c
./src/H5Oshared.c       [NEW]
./src/H5Ostab.c
        Supports shared messages.

./src/H5T.c
./src/H5Tpkg.h
./src/H5Tprivate.h
./src/H5Tpublic.h
        The H5Tshare() function allows the user to give the library
        hints about how a data type will be used.

./test/shtype.c
        Tests the H5Tshare() function.

./test/gheap.c
        Tests the global heap.

./configure.in
./config/BlankForm      [NEW]
./config/alpha-dec
./config/freebsd2.2.1
./config/hpux10.20
./config/irix6.2
./config/irix64
./config/linux
./config/powerpc-ibm-aix4.2.1.0
./config/rs6000-ibm-aix4.1.4.0
./config/solaris2.5
        Cleaned up lots of configuration stuff and made the site
        configuration files lots easier and more uniform.  To make a
        new file grab the BlankForm and modify it.

        By default, debugging is turned on for most packages.  Within
        a package one can use `#ifdef H5AC_DEBUG' to wrap debugging
        code.  Other options are:

           --enable-debug
           --enable-debug=yes
               The default, most but not all packages.

           --disable-debug
           --enable-debug=no
           --enable-debug=none
               The symbol NDEBUG is defined and none of the package
               debug symbols.

           --enable-debug=all
               Debugging is turned on for all packages.  This might
               produce lots of output.

           --enable-debug=g,d
               Debugging is turned on for H5G and H5D.

        A compile mode is also now supported

           --enable-production
           --enable-production=yes
               The library is compiled with optimizations turned on.
               The compiler flags are augmented by adding PROD_CFLAGS
               and PROD_CPPFLAGS which are defined in the site config
               file.

           --disable-production
           --enable-production=no
               The default.  The library is compiled for development
               by including DEBUG_CFLAGS and DEBUG_CPPFLAGS defined in
               the site config file.  This is usually just `-g'.

           --enable-production=profile
           --enable-production=pg
               Builds a library for profiling by including the flags
               from PROFILE_CFLAGS and PROFILE_CPPFLAGS defined in the
               site config file.  This is usullay just `-pg' but it
               could include optimization flags as well depending on
               the type of profile one wants.

        In summary, configure by saying `./configure' and you'll get a
        development version of the library.  Configure by saying
        `./configure --enable-production --disable-debug' and you'll
        get a production version with no debugging code.

29 files changed, 1138 insertions, 439 deletions

diff --git a/src/H5AC.c b/src/H5AC.c
index 23e86e4..9813af7 100644
--- a/src/H5AC.c
+++ b/src/H5AC.c
@@ -641,7 +641,7 @@ H5AC_protect(H5F_t *f, const H5AC_class_t *type, const haddr_t *addr,
 #ifdef H5AC_DEBUG
     static int		    ncalls = 0;
     if (0 == ncalls++) {
-        fprintf(stderr, "HDF5-DIAG: debugging cache (expensive)\n");
+        fprintf(stderr, "H5AC: debugging cache (expensive)\n");
     }
 #endif
 
@@ -838,7 +838,7 @@ H5AC_debug(H5F_t *f)
 
     FUNC_ENTER(H5AC_debug, FAIL);
 
-    fprintf(stderr, "HDF5-DIAG: cache diagnostics for %s\n", f->name);
+    fprintf(stderr, "H5AC: cache diagnostics for %s\n", f->name);
     fprintf(stderr, "   %18s  %8s %8s %8s %8s+%-8s\n",
             "", "Hits", "Misses", "MissRate", "Inits", "Flushes");
 
diff --git a/src/H5B.c b/src/H5B.c
index e061625..86e34ac 100644
--- a/src/H5B.c
+++ b/src/H5B.c
@@ -1640,7 +1640,7 @@ H5B_assert(H5F_t *f, const haddr_t *addr, const H5B_class_t *type,
 
     FUNC_ENTER(H5B_assert, FAIL);
     if (0 == ncalls++) {
-	fprintf(stderr, "HDF5-DIAG: debugging B-trees (expensive)\n");
+	fprintf(stderr, "H5B: debugging B-trees (expensive)\n");
     }
     /* Initialize the queue */
     bt = H5AC_find(f, H5AC_BT, addr, type, udata);
diff --git a/src/H5D.c b/src/H5D.c
index 8a527cd..8df99c0 100644
--- a/src/H5D.c
+++ b/src/H5D.c
@@ -820,7 +820,8 @@ H5D_create(H5G_t *loc, const char *name, const H5T_t *type, const H5S_t *space,
     }
 
     /* Update the type and space header messages */
-    if (H5O_modify(&(new_dset->ent), H5O_DTYPE, 0, H5O_FLAG_CONSTANT,
+    if (H5O_modify(&(new_dset->ent), H5O_DTYPE, 0,
+		   (H5O_FLAG_CONSTANT|H5O_FLAG_SHARED),
 		   new_dset->type) < 0 ||
 	H5S_modify(&(new_dset->ent), new_dset->space) < 0) {
 	HGOTO_ERROR(H5E_DATASET, H5E_CANTINIT, NULL,
@@ -1162,7 +1163,7 @@ H5D_read(H5D_t *dataset, const H5T_t *mem_type, const H5S_t *mem_space,
 				    mem_space, buf/*out*/);
 	if (status>=0) goto succeed;
 #ifdef H5D_DEBUG
-	fprintf (stderr, "HDF5-DIAG: input pipe optimization failed "
+	fprintf (stderr, "H5D: input pipe optimization failed "
 		 "(falling through)\n");
 #endif
 	H5E_clear ();
@@ -1217,7 +1218,7 @@ H5D_read(H5D_t *dataset, const H5T_t *mem_type, const H5S_t *mem_space,
 	/* Strip mine diagnostics.... */
 	size_t buffer_size = smine_nelmts * MAX (src_type_size, dst_type_size);
 	if (smine_nelmts<nelmts) {
-	    fprintf (stderr, "HDF5-DIAG: strip mine");
+	    fprintf (stderr, "H5D: strip mine");
 	    if (smine_nelmts!=request_nelmts) {
 		fprintf (stderr, " got %lu of %lu",
 			 (unsigned long)smine_nelmts,
@@ -1225,10 +1226,10 @@ H5D_read(H5D_t *dataset, const H5T_t *mem_type, const H5S_t *mem_space,
 	    }
 	    if (buffer_size!=target_size) {
 		fprintf (stderr, " (%1.1f%% of buffer)",
-			 100.0*buffer_size/target_size);
+			 100.0*(double)buffer_size/(double)target_size);
 	    }
 	    fprintf (stderr, " %1.1f iterations\n",
-		     (double)nelmts/smine_nelmts);
+		     (double)nelmts/(double)smine_nelmts);
 	}
     }
 #endif
@@ -1388,7 +1389,7 @@ H5D_write(H5D_t *dataset, const H5T_t *mem_type, const H5S_t *mem_space,
 				     mem_space, buf);
 	if (status>=0) goto succeed;
 #ifdef H5D_DEBUG
-	fprintf (stderr, "HDF5-DIAG: output pipe optimization failed "
+	fprintf (stderr, "H5D: output pipe optimization failed "
 		 "(falling through)\n");
 #endif
 	H5E_clear ();
@@ -1443,7 +1444,7 @@ H5D_write(H5D_t *dataset, const H5T_t *mem_type, const H5S_t *mem_space,
 	/* Strip mine diagnostics.... */
 	size_t buffer_size = smine_nelmts * MAX (src_type_size, dst_type_size);
 	if (smine_nelmts<nelmts) {
-	    fprintf (stderr, "HDF5-DIAG: strip mine");
+	    fprintf (stderr, "H5D: strip mine");
 	    if (smine_nelmts!=request_nelmts) {
 		fprintf (stderr, " got %lu of %lu",
 			 (unsigned long)smine_nelmts,
@@ -1451,10 +1452,10 @@ H5D_write(H5D_t *dataset, const H5T_t *mem_type, const H5S_t *mem_space,
 	    }
 	    if (buffer_size!=target_size) {
 		fprintf (stderr, " (%1.1f%% of buffer)",
-			 100.0*buffer_size/target_size);
+			 100.0*(double)buffer_size/(double)target_size);
 	    }
 	    fprintf (stderr, " %1.1f iterations\n",
-		     (double)nelmts/smine_nelmts);
+		     (double)nelmts/(double)smine_nelmts);
 	}
     }
 #endif
diff --git a/src/H5F.c b/src/H5F.c
index 4bec710..f29eec7 100644
--- a/src/H5F.c
+++ b/src/H5F.c
@@ -553,7 +553,7 @@ H5F_dest(H5F_t *f)
  *		following flags which are similar in nature to the Posix
  *		open(2) flags.
  *
- *		H5F_ACC_WRITE:	Open with read/write access. If the file is
+ *		H5F_ACC_RDWR:	Open with read/write access. If the file is
  *				currently open for read-only access then it
  *				will be reopened. Absence of this flag
  *				implies read-only access.
@@ -968,7 +968,7 @@ H5F_open(const char *name, uintn flags,
 	 * hdf5 data.
 	 */
 #ifdef H5F_DEBUG
-	fprintf(stderr, "HDF5-DIAG: resetting EOF from ");
+	fprintf(stderr, "H5F: resetting EOF from ");
 	H5F_addr_print(stderr, &addr1);
 	fprintf(stderr, " to ");
 	H5F_addr_print(stderr, &addr2);
@@ -1323,7 +1323,7 @@ H5F_close(H5F_t *f)
      */
     if (f->nopen>0) {
 #ifndef NDEBUG
-	fprintf(stderr, "HDF5-DIAG: H5F_close: %u object header%s still "
+	fprintf(stderr, "H5F: H5F_close: %u object header%s still "
 		"open (file close will complete when %s closed)\n",
 		f->nopen,
 		1 == f->nopen ? " is" : "s are",
@@ -1333,7 +1333,7 @@ H5F_close(H5F_t *f)
 	HRETURN(SUCCEED);
     } else if (f->close_pending) {
 #ifndef NDEBUG
-	fprintf(stderr, "HDF5-DIAG: H5F_close: operation completed\n");
+	fprintf(stderr, "H5F: H5F_close: operation completed\n");
 #endif
     }
     
diff --git a/src/H5Ffamily.c b/src/H5Ffamily.c
index b89b983..e9596b8 100644
--- a/src/H5Ffamily.c
+++ b/src/H5Ffamily.c
@@ -187,7 +187,7 @@ H5F_fam_open(const char *name, const H5F_access_t *access_parms,
 		if (size != mask) {
 		    size++;
 #ifdef H5F_DEBUG
-		    fprintf(stderr, "HDF5-DIAG: family member size was "
+		    fprintf(stderr, "H5F: family member size was "
 			    "rounded up to a power of 2");
 #endif
 		}
@@ -199,16 +199,16 @@ H5F_fam_open(const char *name, const H5F_access_t *access_parms,
 
 #ifdef H5F_DEBUG
     if (nbits >= 30) {
-	fprintf(stderr, "HDF5-DIAG: family members are %dGB\n",
+	fprintf(stderr, "H5F: family members are %dGB\n",
 		1 << (nbits-30));
     } else if (nbits >= 20) {
-	fprintf(stderr, "HDF5-DIAG: family members are %dMB\n",
+	fprintf(stderr, "H5F: family members are %dMB\n",
 		1 << (nbits-20));
     } else if (nbits >= 10) {
-	fprintf(stderr, "HDF5-DIAG: family members are %dkB\n",
+	fprintf(stderr, "H5F: family members are %dkB\n",
 		1 << (nbits-10));
     } else {
-	fprintf(stderr, "HDF5-DIAG: family members are %d bytes\n",
+	fprintf(stderr, "H5F: family members are %d bytes\n",
 		1 << nbits);
     }
 #endif
diff --git a/src/H5Flow.c b/src/H5Flow.c
index 125f8ed..545659a 100644
--- a/src/H5Flow.c
+++ b/src/H5Flow.c
@@ -283,7 +283,7 @@ H5F_low_write(H5F_low_t *lf, const H5F_access_t *access_parms,
     tmp_addr = *addr;
     H5F_addr_inc(&tmp_addr, size);
     if (H5F_addr_gt(&tmp_addr, &(lf->eof))) {
-        fprintf(stderr, "HDF5-DIAG: extending file w/o allocation\n");
+        fprintf(stderr, "H5F: extending file w/o allocation\n");
         lf->eof = tmp_addr;
     }
     /* Write the data */
@@ -718,7 +718,7 @@ H5F_addr_encode(H5F_t *f, uint8 **pp, const haddr_t *addr)
  *-------------------------------------------------------------------------
  */
 void
-H5F_addr_decode(H5F_t *f, const uint8 **pp, haddr_t *addr /*out */ )
+H5F_addr_decode(H5F_t *f, const uint8 **pp, haddr_t *addr/*out*/)
 {
     int                     i;
     haddr_t                 tmp;
@@ -763,9 +763,9 @@ H5F_addr_decode(H5F_t *f, const uint8 **pp, haddr_t *addr /*out */ )
  *-------------------------------------------------------------------------
  */
 void
-H5F_addr_print(FILE * stream, const haddr_t *addr)
+H5F_addr_print(FILE *stream, const haddr_t *addr)
 {
-    haddr_t                 tmp;
+    haddr_t		tmp;
 
     assert(stream);
     assert(addr);
diff --git a/src/H5HG.c b/src/H5HG.c
index 63b41a3..9af1074 100644
--- a/src/H5HG.c
+++ b/src/H5HG.c
@@ -33,25 +33,20 @@
 
 #define PABLO_MASK	H5HG_mask
 
-struct H5HG_t {
-    haddr_t		addr;		/*address of collection		*/
-    intn		idx;		/*object ID within collection	*/
-};
-
 typedef struct H5HG_obj_t {
     intn		nrefs;		/*reference count		*/
     size_t		size;		/*total size of object		*/
     uint8		*begin;		/*ptr to object into heap->chunk*/
 } H5HG_obj_t;
 
-typedef struct H5HG_heap_t {
+struct H5HG_heap_t {
     haddr_t		addr;		/*collection address		*/
     hbool_t		dirty;		/*does heap need to be saved?	*/
     size_t		size;		/*total size of collection	*/
     uint8		*chunk;		/*the collection, incl. header	*/
     intn		nalloc;		/*numb object slots allocated	*/
     H5HG_obj_t		*obj;		/*array of object descriptions	*/
-} H5HG_heap_t;
+};
 
 /* PRIVATE PROTOTYPES */
 static H5HG_heap_t *H5HG_load(H5F_t *f, const haddr_t *addr,
@@ -81,9 +76,11 @@ static intn interface_initialize_g = FALSE;
  *		new collection is allocated in the file and added to the
  *		beginning of the CWFS list.
  *
- * Return:	Success:	SUCCEED
+ * Return:	Success:	Ptr to a cached heap.  The pointer is valid
+ *				only until some other hdf5 library function
+ *				is called.
  *
- *		Failure:	FAIL
+ *		Failure:	NULL
  *
  * Programmer:	Robb Matzke
  *              Friday, March 27, 1998
@@ -92,15 +89,15 @@ static intn interface_initialize_g = FALSE;
  *
  *-------------------------------------------------------------------------
  */
-herr_t
+H5HG_heap_t *
 H5HG_create (H5F_t *f, size_t size)
 {
     H5HG_heap_t	*heap = NULL;
-    herr_t	ret_value = FAIL;
+    H5HG_heap_t	*ret_value = NULL;
     uint8	*p = NULL;
     haddr_t	addr;
     
-    FUNC_ENTER (H5HG_create, FAIL);
+    FUNC_ENTER (H5HG_create, NULL);
 
     /* Check args */
     assert (f);
@@ -108,7 +105,7 @@ H5HG_create (H5F_t *f, size_t size)
 
     /* Create it */
     if (H5MF_alloc (f, H5MF_META, size, &addr/*out*/)<0) {
-	HGOTO_ERROR (H5E_HEAP, H5E_CANTINIT, FAIL,
+	HGOTO_ERROR (H5E_HEAP, H5E_CANTINIT, NULL,
 		     "unable to allocate file space for global heap");
     }
     heap = H5MM_xcalloc (1, sizeof(H5HG_heap_t));
@@ -123,7 +120,9 @@ H5HG_create (H5F_t *f, size_t size)
     HDmemcpy (heap->chunk, H5HG_MAGIC, H5HG_SIZEOF_MAGIC);
     p = heap->chunk + H5HG_SIZEOF_MAGIC;
     *p++ = H5HG_VERSION;
-    p += 3; /*reserved*/
+    *p++ = 0; /*reserved*/
+    *p++ = 0; /*reserved*/
+    *p++ = 0; /*reserved*/
     H5F_encode_length (f, p, size);
 
     /* The freespace object */
@@ -136,7 +135,7 @@ H5HG_create (H5F_t *f, size_t size)
 
     /* Add the heap to the cache */
     if (H5AC_set (f, H5AC_GHEAP, &addr, heap)<0) {
-	HGOTO_ERROR (H5E_HEAP, H5E_CANTINIT, FAIL,
+	HGOTO_ERROR (H5E_HEAP, H5E_CANTINIT, NULL,
 		     "unable to cache global heap collection");
     }
 
@@ -152,10 +151,10 @@ H5HG_create (H5F_t *f, size_t size)
 	f->shared->ncwfs = MIN (H5HG_NCWFS, f->shared->ncwfs+1);
     }
 
-    ret_value = SUCCEED;
+    ret_value = heap;
 
  done:
-    if (ret_value<0 && heap) {
+    if (!ret_value && heap) {
 	H5MM_xfree (heap->chunk);
 	H5MM_xfree (heap->obj);
 	H5MM_xfree (heap);
@@ -263,7 +262,7 @@ H5HG_load (H5F_t *f, const haddr_t *addr, const void *udata1, void *udata2)
 	    UINT16DECODE (p, heap->obj[idx].nrefs);
 	    H5F_decode_length (f, p, heap->obj[idx].size);
 	    heap->obj[idx].begin = begin;
-	    p += heap->obj[idx].size;
+	    p = begin + heap->obj[idx].size;
 	}
     }
     assert (p==heap->chunk+heap->size);
@@ -502,8 +501,8 @@ H5HG_insert (H5F_t *f, size_t size, void *obj, H5HG_t *hobj/*out*/)
 		f->shared->cwfs[cwfsno] = f->shared->cwfs[cwfsno-1];
 		f->shared->cwfs[cwfsno-1] = tmp;
 		--cwfsno;
-		break;
 	    }
+	    break;
 	}
     }
 
@@ -512,11 +511,12 @@ H5HG_insert (H5F_t *f, size_t size, void *obj, H5HG_t *hobj/*out*/)
      * new collection large enough for the message plus the collection header.
      */
     if (cwfsno>=f->shared->ncwfs) {
-	if (H5HG_create (f, need+H5HG_SIZEOF_HDR (f))<0) {
+	if (NULL==(heap=H5HG_create (f, need+H5HG_SIZEOF_HDR (f)))) {
 	    HRETURN_ERROR (H5E_HEAP, H5E_CANTINIT, FAIL,
 			   "unable to allocate a global heap collection");
 	}
 	assert (f->shared->ncwfs>0);
+	assert (f->shared->cwfs[0]==heap);
 	assert (f->shared->cwfs[0]->obj[0].size >= need+H5HG_SIZEOF_HDR(f));
 	cwfsno = 0;
     }
@@ -763,6 +763,8 @@ H5HG_remove (H5F_t *f, H5HG_t *hobj)
 	heap->obj[0].begin = heap->chunk + (heap->size-size);
 	heap->obj[0].size = size;
 	heap->obj[0].nrefs = 0;
+    } else {
+	heap->obj[0].size += size;
     }
     HDmemmove (obj_start, obj_start+size,
 	       heap->size-((obj_start+size)-heap->chunk));
@@ -830,9 +832,11 @@ herr_t
 H5HG_debug(H5F_t *f, const haddr_t *addr, FILE *stream, intn indent,
 	  intn fwidth)
 {
-    int			i, nused, maxobj;
+    int			i, j, k, nused, maxobj;
     H5HG_heap_t		*h = NULL;
     char		buf[64];
+    size_t		size;
+    uint8		*p = NULL;
 
     FUNC_ENTER(H5HG_debug, FAIL);
 
@@ -873,13 +877,31 @@ H5HG_debug(H5F_t *f, const haddr_t *addr, FILE *stream, intn indent,
     for (i=1; i<h->nalloc; i++) {
 	if (h->obj[i].begin) {
 	    sprintf (buf, "Object %d", i);
-	    fprintf (stream, "%*s%-*s:\n", indent, "", fwidth, buf);
+	    fprintf (stream, "%*s%s\n", indent, "", buf);
 	    fprintf (stream, "%*s%-*s %d\n", indent+3, "", MIN(fwidth-3, 0),
 		     "Reference count:",
 		     h->obj[i].nrefs);
 	    fprintf (stream, "%*s%-*s %lu\n", indent+3, "", MIN(fwidth-3, 0),
 		     "Size of object body:",
 		     (unsigned long)(h->obj[i].size));
+	    size = h->obj[i].size - H5HG_SIZEOF_OBJHDR (f);
+	    p = h->obj[i].begin + H5HG_SIZEOF_OBJHDR (f);
+	    for (j=0; j<size; j+=16) {
+		fprintf (stream, "%*s%04d: ", indent+6, "", j);
+		for (k=0; k<16; k++) {
+		    if (8==k) fprintf (stream, " ");
+		    if (j+k<size) {
+			fprintf (stream, "%02x ", p[j+k]);
+		    } else {
+			fputs ("   ", stream);
+		    }
+		}
+		for (k=0; k<16 && j+k<size; k++) {
+		    if (8==k) fprintf (stream, " ");
+		    fputc (p[j+k]>' ' && p[j+k]<='~' ? p[j+k] : '.', stream);
+		}
+		fprintf (stream, "\n");
+	    }
 	}
     }
     
diff --git a/src/H5HGprivate.h b/src/H5HGprivate.h
index aebb3f8..c6ec1cd 100644
--- a/src/H5HGprivate.h
+++ b/src/H5HGprivate.h
@@ -10,6 +10,8 @@
 
 #include <H5HGpublic.h>
 
+#include <H5Fprivate.h>
+
 /*
  * Each collection has a magic number for some redundancy.
  */
@@ -59,14 +61,27 @@
  * The initial guess for the number of messages in a collection.  We assume
  * that all objects in that collection are zero length, giving the maximum
  * possible number of objects in the collection.  The collection itself has
- * some overhead and each message has some overhead.
+ * some overhead and each message has some overhead.  The `+2' accounts for
+ * rounding and for the free space object.
  */
 #define H5HG_NOBJS(f,z) (int)((((z)-H5HG_SIZEOF_HDR(f))/		      \
-			       H5HG_SIZEOF_OBJHDR(f)+1))
+			       H5HG_SIZEOF_OBJHDR(f)+2))
+
+/*
+ * Makes a global heap object pointer undefined, or checks whether one is
+ * defined.
+ */
+#define H5HG_undef(HGP)	((HGP)->idx=0)
+#define H5HG_defined(HGP) ((HGP)->idx!=0)
+
+typedef struct H5HG_t {
+    haddr_t		addr;		/*address of collection		*/
+    intn		idx;		/*object ID within collection	*/
+} H5HG_t;
 
-typedef struct H5HG_t H5HG_t;
+typedef struct H5HG_heap_t H5HG_heap_t;
 
-herr_t H5HG_create (H5F_t *f, size_t size);
+H5HG_heap_t *H5HG_create (H5F_t *f, size_t size);
 herr_t H5HG_insert (H5F_t *f, size_t size, void *obj, H5HG_t *hobj/*out*/);
 void *H5HG_peek (H5F_t *f, H5HG_t *hobj);
 void *H5HG_read (H5F_t *f, H5HG_t *hobj, void *object);
diff --git a/src/H5HL.c b/src/H5HL.c
index f6fa4f0..8c141a0 100644
--- a/src/H5HL.c
+++ b/src/H5HL.c
@@ -529,9 +529,6 @@ H5HL_insert(H5F_t *f, const haddr_t *addr, size_t buf_size, const void *buf)
     size_t	offset = 0;
     size_t	need_size, old_size, need_more;
     hbool_t	found;
-#ifndef NDEBUG
-    static int	nmessages = 0;
-#endif
 
     FUNC_ENTER(H5HL_insert, (size_t)(-1));
 
@@ -601,14 +598,10 @@ H5HL_insert(H5F_t *f, const haddr_t *addr, size_t buf_size, const void *buf)
 	    assert (max_fl->size==H5HL_ALIGN (max_fl->size));
 
 	    if (max_fl->size < H5HL_SIZEOF_FREE(f)) {
-#ifndef NDEBUG
+#ifdef H5HL_DEBUG
 		if (max_fl->size) {
-		    fprintf(stderr, "H5HL_insert: lost %lu bytes at line %d\n",
-			    (unsigned long) (max_fl->size), __LINE__);
-		    if (0 == nmessages++) {
-			fprintf(stderr, "Messages from H5HL_insert() will go "
-				"away when assertions are turned off.\n");
-		    }
+		    fprintf(stderr, "H5HL: lost %lu bytes at line %d\n",
+			    (unsigned long)(max_fl->size), __LINE__);
 		}
 #endif
 		max_fl = H5HL_remove_free(heap, max_fl);
@@ -629,26 +622,18 @@ H5HL_insert(H5F_t *f, const haddr_t *addr, size_t buf_size, const void *buf)
 		fl->next = heap->freelist;
 		if (heap->freelist) heap->freelist->prev = fl;
 		heap->freelist = fl;
-#ifndef NDEBUG
+#ifdef H5HL_DEBUG
 	    } else if (need_more > need_size) {
 		fprintf(stderr, "H5HL_insert: lost %lu bytes at line %d\n",
-			(unsigned long) (need_more - need_size), __LINE__);
-		if (0 == nmessages++) {
-		    fprintf(stderr, "Messages from H5HL_insert() will go away "
-			    "when assertions are turned off.\n");
-		}
+			(unsigned long)(need_more - need_size), __LINE__);
 #endif
 	    }
 	}
 
-#ifndef NDEBUG
-	fprintf(stderr, "H5HL_insert: resize mem buf from %lu to %lu bytes\n",
-		(unsigned long) (heap->mem_alloc),
-		(unsigned long) (heap->mem_alloc + need_more));
-	if (0 == nmessages++) {
-	    fprintf(stderr, "Messages from H5HL_insert() will go away "
-		    "when assertions are turned off.\n");
-	}
+#ifdef H5HL_DEBUG
+	fprintf(stderr, "H5HL: resize mem buf from %lu to %lu bytes\n",
+		(unsigned long)(heap->mem_alloc),
+		(unsigned long)(heap->mem_alloc + need_more));
 #endif
 	old_size = heap->mem_alloc;
 	heap->mem_alloc += need_more;
@@ -748,9 +733,6 @@ H5HL_remove(H5F_t *f, const haddr_t *addr, size_t offset, size_t size)
 {
     H5HL_t		*heap = NULL;
     H5HL_free_t		*fl = heap->freelist, *fl2 = NULL;
-#ifndef NDEBUG
-    static int		nmessages = 0;
-#endif
 
     FUNC_ENTER(H5HL_remove, FAIL);
 
@@ -817,12 +799,8 @@ H5HL_remove(H5F_t *f, const haddr_t *addr, size_t offset, size_t size)
      * lost.
      */
     if (size < H5HL_SIZEOF_FREE(f)) {
-#ifndef NDEBUG
-	fprintf(stderr, "H5HL_remove: lost %lu bytes\n", (unsigned long) size);
-	if (0 == nmessages++) {
-	    fprintf(stderr, "Messages from H5HL_remove() will go away "
-		    "when assertions are turned off.\n");
-	}
+#ifdef H5HL_DEBUG
+	fprintf(stderr, "H5HL: lost %lu bytes\n", (unsigned long) size);
 #endif
 	HRETURN(SUCCEED);
     }
diff --git a/src/H5HLprivate.h b/src/H5HLprivate.h
index 8ccc2ed..b1af51a 100644
--- a/src/H5HLprivate.h
+++ b/src/H5HLprivate.h
@@ -23,6 +23,14 @@
 #include <H5private.h>
 #include <H5Fprivate.h>
 
+/*
+ * Feature: Define H5HL_DEBUG on the compiler command line if you want to
+ *	    diagnostic messages from this layer.
+ */
+#ifdef NDEBUG
+#  undef H5HL_DEBUG
+#endif
+
 #define H5HL_MAGIC	"HEAP"		/*heap magic number		     */
 #define H5HL_SIZEOF_MAGIC 4
 
diff --git a/src/H5MF.c b/src/H5MF.c
index 8985490..46d5bae 100644
--- a/src/H5MF.c
+++ b/src/H5MF.c
@@ -116,7 +116,7 @@ H5MF_free(H5F_t *f, const haddr_t *addr, size_t size)
         HRETURN(SUCCEED);
     assert(!H5F_addr_zerop(addr));
 
-#ifndef NDEBUG
+#ifdef H5MF_DEBUG
     fprintf(stderr, "H5MF_free: lost %lu bytes of file storage\n",
             (unsigned long) size);
 #endif
diff --git a/src/H5MFprivate.h b/src/H5MFprivate.h
index 403da90..739966a 100644
--- a/src/H5MFprivate.h
+++ b/src/H5MFprivate.h
@@ -23,6 +23,14 @@
 #include <H5private.h>
 #include <H5Fprivate.h>
 
+/*
+ * Feature: Define H5MF_DEBUG on the compiler command line if you want to
+ *	    see diagnostics from this layer.
+ */
+#ifdef NDEBUG
+#  undef H5MF_DEBUG
+#endif
+
 #define H5MF_META       0               /*request storage for meta data      */
 #define H5MF_RAW        1               /*request storage for raw data       */
 
diff --git a/src/H5O.c b/src/H5O.c
index bf60b09..87f29fc 100644
--- a/src/H5O.c
+++ b/src/H5O.c
@@ -107,6 +107,7 @@ H5O_init_interface(void)
 
     FUNC_LEAVE(SUCCEED);
 }
+
 
 /*-------------------------------------------------------------------------
  * Function:	H5O_create
@@ -281,6 +282,7 @@ H5O_close(H5G_entry_t *obj_ent)
 
     FUNC_LEAVE(SUCCEED);
 }
+
 
 /*-------------------------------------------------------------------------
  * Function:	H5O_load
@@ -317,7 +319,7 @@ H5O_load(H5F_t *f, const haddr_t *addr, const void *_udata1, void *_udata2)
     haddr_t	chunk_addr;
     size_t	chunk_size;
     H5O_cont_t	*cont = NULL;
-    hbool_t	constant;	/*is message a constant mesg?	*/
+    uint8	flags;
 
     FUNC_ENTER(H5O_load, NULL);
 
@@ -392,14 +394,8 @@ H5O_load(H5F_t *f, const haddr_t *addr, const void *_udata1, void *_udata2)
 	    UINT16DECODE(p, id);
 	    UINT16DECODE(p, mesg_size);
 	    assert (mesg_size==H5O_ALIGN (mesg_size));
-	    p += 4; /*reserved*/
-
-	    /*
-	     * The message ID field actually contains some bits near the
-	     * high-order end that are not part of the ID.
-	     */
-	    constant = (id & H5O_FLAG_CONSTANT) ? TRUE : FALSE;
-	    id &= ~H5O_FLAG_BITS;
+	    flags = *p++;
+	    p += 3; /*reserved*/
 
 	    if (id >= NELMTS(message_type_g) || NULL == message_type_g[id]) {
 		HGOTO_ERROR(H5E_OHDR, H5E_BADMESG, NULL,
@@ -424,7 +420,7 @@ H5O_load(H5F_t *f, const haddr_t *addr, const void *_udata1, void *_udata2)
 		mesgno = oh->nmesgs++;
 		oh->mesg[mesgno].type = message_type_g[id];
 		oh->mesg[mesgno].dirty = FALSE;
-		oh->mesg[mesgno].constant = constant;
+		oh->mesg[mesgno].flags = flags;
 		oh->mesg[mesgno].native = NULL;
 		oh->mesg[mesgno].raw = p;
 		oh->mesg[mesgno].raw_size = mesg_size;
@@ -439,7 +435,7 @@ H5O_load(H5F_t *f, const haddr_t *addr, const void *_udata1, void *_udata2)
 	     curmesg++) {
 	    if (H5O_CONT_ID == oh->mesg[curmesg].type->id) {
 		uint8 *p2 = oh->mesg[curmesg].raw;
-		cont = (H5O_CONT->decode) (f, oh->mesg[curmesg].raw_size, p2);
+		cont = (H5O_CONT->decode) (f, p2, NULL);
 		oh->mesg[curmesg].native = cont;
 		chunk_addr = cont->addr;
 		chunk_size = cont->size;
@@ -464,6 +460,7 @@ H5O_load(H5F_t *f, const haddr_t *addr, const void *_udata1, void *_udata2)
     }
     FUNC_LEAVE(ret_value);
 }
+
 
 /*-------------------------------------------------------------------------
  * Function:	H5O_flush
@@ -491,6 +488,7 @@ H5O_flush(H5F_t *f, hbool_t destroy, const haddr_t *addr, H5O_t *oh)
     uint8	buf[16], *p;
     intn	i, id;
     H5O_cont_t	*cont = NULL;
+    herr_t	(*encode)(H5F_t*, uint8*, const void*) = NULL;
 
     FUNC_ENTER(H5O_flush, FAIL);
 
@@ -532,12 +530,10 @@ H5O_flush(H5F_t *f, hbool_t destroy, const haddr_t *addr, H5O_t *oh)
 	    if (oh->mesg[i].dirty) {
 		p = oh->mesg[i].raw - H5O_SIZEOF_MSGHDR(f);
 
-		/* The message id has some flags in the high-order bits. */
 		id = oh->mesg[i].type->id;
-		id |= oh->mesg[i].constant ? H5O_FLAG_CONSTANT : 0;
 		UINT16ENCODE(p, id);
 		UINT16ENCODE(p, oh->mesg[i].raw_size);
-		*p++ = 0; /*reserved*/
+		*p++ = oh->mesg[i].flags;
 		*p++ = 0; /*reserved*/
 		*p++ = 0; /*reserved*/
 		*p++ = 0; /*reserved*/
@@ -563,7 +559,11 @@ H5O_flush(H5F_t *f, hbool_t destroy, const haddr_t *addr, H5O_t *oh)
 			oh->chunk[cont->chunkno].addr = cont->addr;
 		    }
 		    
-		    /* encode the message */
+		    /*
+		     * Encode the message.  If the message is shared then we
+		     * encode a Shared Object message instead of the object
+		     * which is being shared.
+		     */
 		    assert(oh->mesg[i].raw >=
 			   oh->chunk[oh->mesg[i].chunkno].image);
 		    assert (oh->mesg[i].raw_size ==
@@ -571,9 +571,12 @@ H5O_flush(H5F_t *f, hbool_t destroy, const haddr_t *addr, H5O_t *oh)
 		    assert(oh->mesg[i].raw + oh->mesg[i].raw_size <=
 			   oh->chunk[oh->mesg[i].chunkno].image +
 			   oh->chunk[oh->mesg[i].chunkno].size);
-		    if ((oh->mesg[i].type->encode) (f, oh->mesg[i].raw_size,
-						    oh->mesg[i].raw,
-						    oh->mesg[i].native) < 0) {
+		    if (oh->mesg[i].flags & H5O_FLAG_SHARED) {
+			encode = H5O_SHARED->encode;
+		    } else {
+			encode = oh->mesg[i].type->encode;
+		    }
+		    if ((encode)(f, oh->mesg[i].raw, oh->mesg[i].native)<0) {
 			HRETURN_ERROR(H5E_OHDR, H5E_CANTENCODE, FAIL,
 				  "unable to encode object header message");
 		    }
@@ -607,7 +610,11 @@ H5O_flush(H5F_t *f, hbool_t destroy, const haddr_t *addr, H5O_t *oh)
 
 	/* destroy messages */
 	for (i = 0; i < oh->nmesgs; i++) {
-	    H5O_reset(oh->mesg[i].type, oh->mesg[i].native);
+	    if (oh->mesg[i].flags & H5O_FLAG_SHARED) {
+		H5O_reset (H5O_SHARED, oh->mesg[i].native);
+	    } else {
+		H5O_reset(oh->mesg[i].type, oh->mesg[i].native);
+	    }
 	    oh->mesg[i].native = H5MM_xfree(oh->mesg[i].native);
 	}
 	oh->mesg = H5MM_xfree(oh->mesg);
@@ -617,6 +624,7 @@ H5O_flush(H5F_t *f, hbool_t destroy, const haddr_t *addr, H5O_t *oh)
     }
     FUNC_LEAVE(SUCCEED);
 }
+
 
 /*-------------------------------------------------------------------------
  * Function:	H5O_reset
@@ -654,6 +662,7 @@ H5O_reset(const H5O_class_t *type, void *native)
     }
     FUNC_LEAVE(SUCCEED);
 }
+
 
 /*-------------------------------------------------------------------------
  * Function:	H5O_link
@@ -676,8 +685,8 @@ H5O_reset(const H5O_class_t *type, void *native)
 intn
 H5O_link(H5G_entry_t *ent, intn adjust)
 {
-    H5O_t		   *oh = NULL;
-    intn		    ret_value = FAIL;
+    H5O_t	*oh = NULL;
+    intn	ret_value = FAIL;
 
     FUNC_ENTER(H5O_link, FAIL);
 
@@ -714,6 +723,7 @@ H5O_link(H5G_entry_t *ent, intn adjust)
     }
     FUNC_LEAVE(ret_value);
 }
+
 
 /*-------------------------------------------------------------------------
  * Function:	H5O_read
@@ -739,11 +749,11 @@ H5O_link(H5G_entry_t *ent, intn adjust)
 void *
 H5O_read(H5G_entry_t *ent, const H5O_class_t *type, intn sequence, void *mesg)
 {
-    H5O_t		   *oh = NULL;
-    void		   *retval = NULL;
-    intn		    idx;
-    H5G_cache_t		   *cache = NULL;
-    H5G_type_t		    cache_type;
+    H5O_t		*oh = NULL;
+    void		*ret_value = NULL;
+    intn		idx;
+    H5G_cache_t		*cache = NULL;
+    H5G_type_t		cache_type;
 
     FUNC_ENTER(H5O_read, NULL);
 
@@ -757,9 +767,9 @@ H5O_read(H5G_entry_t *ent, const H5O_class_t *type, intn sequence, void *mesg)
     /* can we get it from the symbol table entry? */
     cache = H5G_ent_cache(ent, &cache_type);
     if (H5O_fast_g[cache_type]) {
-	retval = (H5O_fast_g[cache_type]) (cache, type, mesg);
-	if (retval)
-	    HRETURN(retval);
+	ret_value = (H5O_fast_g[cache_type]) (cache, type, mesg);
+	if (ret_value)
+	    HRETURN(ret_value);
 	H5E_clear(); /*don't care, try reading from header */
     }
 
@@ -776,19 +786,54 @@ H5O_read(H5G_entry_t *ent, const H5O_class_t *type, intn sequence, void *mesg)
 	HRETURN_ERROR(H5E_OHDR, H5E_CANTLOAD, NULL,
 		      "unable to load object header");
     }
-    retval = (type->copy) (oh->mesg[idx].native, mesg);
+    if (oh->mesg[idx].flags & H5O_FLAG_SHARED) {
+	/*
+	 * If the message is shared then then the native pointer points to an
+	 * H5O_SHARED message.  We use that information to look up the real
+	 * message in the global heap.
+	 */
+	H5O_shared_t *shared;
+	void *tmp_buf, *tmp_mesg;
+
+	shared = (H5O_shared_t *)(oh->mesg[idx].native);
+	if (NULL==(tmp_buf = H5HG_read (ent->file, shared, NULL))) {
+	    HGOTO_ERROR (H5E_OHDR, H5E_CANTLOAD, NULL,
+			 "unable to read shared message from global heap");
+	}
+	tmp_mesg = (type->decode)(ent->file, tmp_buf, shared);
+	if (!tmp_mesg) {
+	    H5MM_xfree (tmp_buf);
+	    HGOTO_ERROR (H5E_OHDR, H5E_CANTLOAD, NULL,
+			 "unable to decode object header shared message");
+	}
+	if (mesg) {
+	    HDmemcpy (mesg, tmp_mesg, type->native_size);
+	    H5MM_xfree (tmp_mesg);
+	} else {
+	    ret_value = tmp_mesg;
+	}
+    } else {
+	/*
+	 * The message is not shared, but rather exists in the object
+	 * header.  The object header caches the native message (along with
+	 * the raw message) so we must copy the native message before
+	 * returning.
+	 */
+	if (NULL==(ret_value = (type->copy) (oh->mesg[idx].native, mesg))) {
+	    HGOTO_ERROR (H5E_OHDR, H5E_CANTINIT, NULL,
+			 "unable to copy message to user space");
+	}
+    }
+
+ done:
     if (H5AC_unprotect(ent->file, H5AC_OHDR, &(ent->header), oh) < 0) {
 	HRETURN_ERROR(H5E_OHDR, H5E_PROTECT, NULL,
 		      "unable to release object header");
     }
     oh = NULL;
-
-    if (!retval) {
-	HRETURN_ERROR(H5E_OHDR, H5E_CANTINIT, NULL,
-		      "unable to copy object header message to user space");
-    }
-    FUNC_LEAVE(retval);
+    FUNC_LEAVE(ret_value);
 }
+
 
 /*-------------------------------------------------------------------------
  * Function:	H5O_find_in_ohdr
@@ -812,23 +857,24 @@ static intn
 H5O_find_in_ohdr(H5F_t *f, const haddr_t *addr, const H5O_class_t **type_p,
 		 intn sequence)
 {
-    H5O_t		   *oh = NULL;
-    int			    i;
+    H5O_t		*oh = NULL;
+    int			i;
+    const H5O_class_t	*type = NULL;
 
     FUNC_ENTER(H5O_find_in_ohdr, FAIL);
 
-    /* check args */
+    /* Check args */
     assert(f);
     assert(addr && H5F_addr_defined(addr));
     assert(type_p);
 
-    /* load the object header */
+    /* Load the object header */
     if (NULL == (oh = H5AC_find(f, H5AC_OHDR, addr, NULL, NULL))) {
 	HRETURN_ERROR(H5E_OHDR, H5E_CANTLOAD, FAIL,
 		      "unable to load object header");
     }
 
-    /* scan through the messages looking for the right one */
+    /* Scan through the messages looking for the right one */
     for (i = 0; i < oh->nmesgs; i++) {
 	if (*type_p && (*type_p)->id != oh->mesg[i].type->id) continue;
 	if (--sequence < 0) break;
@@ -838,24 +884,32 @@ H5O_find_in_ohdr(H5F_t *f, const haddr_t *addr, const H5O_class_t **type_p,
 		      "unable to find object header message");
     }
 
-    /* decode the message if necessary */
+    /*
+     * Decode the message if necessary.  If the message is shared then decode
+     * a shared message, ignoring the message type.
+     */
+    if (oh->mesg[i].flags & H5O_FLAG_SHARED) {
+	type = H5O_SHARED;
+    } else {
+	type = oh->mesg[i].type;
+    }
     if (NULL == oh->mesg[i].native) {
-	assert(oh->mesg[i].type->decode);
-	assert (oh->mesg[i].raw_size==H5O_ALIGN (oh->mesg[i].raw_size));
-	oh->mesg[i].native = (oh->mesg[i].type->decode) (f,
-							 oh->mesg[i].raw_size,
-							 oh->mesg[i].raw);
+	assert(type->decode);
+	oh->mesg[i].native = (type->decode) (f, oh->mesg[i].raw, NULL);
 	if (NULL == oh->mesg[i].native) {
 	    HRETURN_ERROR(H5E_OHDR, H5E_CANTDECODE, FAIL,
 			  "unable to decode message");
 	}
     }
 
-    /*return the message type */
+    /*
+     * Return the message type. If this is a shared message then return the
+     * pointed-to type.
+     */
     *type_p = oh->mesg[i].type;
-
     FUNC_LEAVE(i);
 }
+
 
 /*-------------------------------------------------------------------------
  * Function:	H5O_modify
@@ -898,10 +952,11 @@ intn
 H5O_modify(H5G_entry_t *ent, const H5O_class_t *type, intn overwrite,
 	   uintn flags, const void *mesg)
 {
-    H5O_t		   *oh = NULL;
-    intn		    idx, sequence;
-    intn		    ret_value = FAIL;
-    size_t		    size;
+    H5O_t		*oh = NULL;
+    intn		idx, sequence;
+    intn		ret_value = FAIL;
+    size_t		size = 0;
+    H5O_shared_t	*sh_mesg = NULL;
 
     FUNC_ENTER(H5O_modify, FAIL);
 
@@ -911,6 +966,7 @@ H5O_modify(H5G_entry_t *ent, const H5O_class_t *type, intn overwrite,
     assert(H5F_addr_defined(&(ent->header)));
     assert(type);
     assert(mesg);
+    assert (0==(flags & ~H5O_FLAG_BITS));
 
     if (NULL == (oh = H5AC_protect(ent->file, H5AC_OHDR, &(ent->header),
 				   NULL, NULL))) {
@@ -937,27 +993,59 @@ H5O_modify(H5G_entry_t *ent, const H5O_class_t *type, intn overwrite,
     }
     if (overwrite < 0) {
 	/* Allocate space for the new message */
-	size = (type->raw_size) (ent->file, mesg);
+	if (flags & H5O_FLAG_SHARED) {
+	    if (NULL==type->share) {
+		HGOTO_ERROR (H5E_OHDR, H5E_UNSUPPORTED, FAIL,
+			     "message class is not sharable");
+	    }
+	    sh_mesg = H5MM_xcalloc (1, sizeof *sh_mesg);
+	    if ((type->share)(ent->file, mesg, sh_mesg/*out*/)<0) {
+		/*
+		 * If the message isn't shared then turn of the shared bit
+		 * and treat it as an unshared message.
+		 */
+		H5E_clear ();
+		flags &= ~H5O_FLAG_SHARED;
+	    } else {
+		if (H5HG_link (ent->file, sh_mesg, 1)<0) {
+		    HGOTO_ERROR (H5E_OHDR, H5E_LINK, FAIL,
+				 "unable to adjust shared object link count");
+		}
+		size = (H5O_SHARED->raw_size)(ent->file, sh_mesg);
+	    }
+	}
+	if (0==(flags & H5O_FLAG_SHARED)) {
+	    size = (type->raw_size) (ent->file, mesg);
+	}
 	size = H5O_ALIGN(size);
 	idx = H5O_alloc(ent->file, oh, type, size);
 	if (idx < 0) {
 	    HGOTO_ERROR(H5E_OHDR, H5E_CANTINIT, FAIL,
-		      "unable to allocate object header space for message");
+			"unable to allocate space for message");
 	}
 	sequence++;
-
-    } else if (oh->mesg[idx].constant) {
+	    
+    } else if (oh->mesg[idx].flags & H5O_FLAG_CONSTANT) {
 	HGOTO_ERROR(H5E_OHDR, H5E_WRITEERROR, FAIL,
 		    "unable to modify constant message");
+    } else if (oh->mesg[idx].flags & H5O_FLAG_SHARED) {
+	HGOTO_ERROR (H5E_OHDR, H5E_WRITEERROR, FAIL,
+		     "unable to modify shared (constant) message");
     }
+    
 
     /* Copy the native value into the object header */
-    oh->mesg[idx].native = (type->copy) (mesg, oh->mesg[idx].native);
-    if (NULL == oh->mesg[idx].native) {
-	HGOTO_ERROR(H5E_OHDR, H5E_CANTINIT, FAIL,
-		    "unable to copy message to object header");
+    if (flags & H5O_FLAG_SHARED) {
+	oh->mesg[idx].native = sh_mesg;
+    } else {
+	oh->mesg[idx].native = (type->copy) (mesg, oh->mesg[idx].native);
+	if (NULL == oh->mesg[idx].native) {
+	    HGOTO_ERROR(H5E_OHDR, H5E_CANTINIT, FAIL,
+			"unable to copy message to object header");
+	}
     }
-    oh->mesg[idx].constant = (flags & H5O_FLAG_CONSTANT) ? TRUE : FALSE;
+    
+    oh->mesg[idx].flags = flags;
     oh->mesg[idx].dirty = TRUE;
     oh->dirty = TRUE;
     ret_value = sequence;
@@ -967,8 +1055,10 @@ H5O_modify(H5G_entry_t *ent, const H5O_class_t *type, intn overwrite,
 	HRETURN_ERROR(H5E_OHDR, H5E_PROTECT, FAIL,
 		      "unable to release object header");
     }
+    
     FUNC_LEAVE(ret_value);
 }
+
 
 /*-------------------------------------------------------------------------
  * Function:	H5O_remove
@@ -1000,9 +1090,10 @@ H5O_modify(H5G_entry_t *ent, const H5O_class_t *type, intn overwrite,
 herr_t
 H5O_remove(H5G_entry_t *ent, const H5O_class_t *type, intn sequence)
 {
-    H5O_t		   *oh = NULL;
-    intn		    i, seq, nfailed = 0;
-    herr_t		    ret_value = FAIL;
+    H5O_t		*oh = NULL;
+    intn		i, seq, nfailed = 0;
+    herr_t		ret_value = FAIL;
+    H5O_shared_t	*sh_mesg = NULL;
 
     FUNC_ENTER(H5O_remove, FAIL);
 
@@ -1018,6 +1109,7 @@ H5O_remove(H5G_entry_t *ent, const H5O_class_t *type, intn sequence)
 	HGOTO_ERROR(H5E_OHDR, H5E_CANTLOAD, FAIL,
 		    "unable to load object header");
     }
+    
     for (i = seq = 0; i < oh->nmesgs; i++) {
 	if (type->id != oh->mesg[i].type->id) continue;
 	if (seq++ == sequence || H5O_ALL == sequence) {
@@ -1025,11 +1117,27 @@ H5O_remove(H5G_entry_t *ent, const H5O_class_t *type, intn sequence)
 	     * Keep track of how many times we failed trying to remove constant
 	     * messages.
 	     */
-	    if (oh->mesg[i].constant) {
+	    if (oh->mesg[i].flags & H5O_FLAG_CONSTANT) {
 		nfailed++;
 		continue;
 	    }
 
+	    if (oh->mesg[i].flags & H5O_FLAG_SHARED) {
+		if (NULL==oh->mesg[i].native) {
+		    sh_mesg = (H5O_SHARED->decode)(ent->file, oh->mesg[i].raw,
+						   NULL);
+		    if (NULL==(oh->mesg[i].native = sh_mesg)) {
+			HGOTO_ERROR (H5E_OHDR, H5E_CANTDECODE, FAIL,
+				     "unable to decode shared message info");
+		    }
+		}
+		if (H5HG_link (ent->file, sh_mesg, -1)<0) {
+		    HGOTO_ERROR (H5E_OHDR, H5E_LINK, FAIL,
+				 "unable to decrement link count on shared "
+				 "message");
+		}
+	    }
+
 	    /* change message type to nil and zero it */
 	    oh->mesg[i].type = H5O_NULL;
 	    HDmemset(oh->mesg[i].raw, 0, oh->mesg[i].raw_size);
@@ -1055,6 +1163,7 @@ H5O_remove(H5G_entry_t *ent, const H5O_class_t *type, intn sequence)
     }
     FUNC_LEAVE(ret_value);
 }
+
 
 /*-------------------------------------------------------------------------
  * Function:	H5O_alloc_extend_chunk
@@ -1083,9 +1192,9 @@ H5O_remove(H5G_entry_t *ent, const H5O_class_t *type, intn sequence)
 static intn
 H5O_alloc_extend_chunk(H5O_t *oh, intn chunkno, size_t size)
 {
-    intn		    idx, i;
-    size_t		    delta;
-    uint8		   *old_addr;
+    intn	idx, i;
+    size_t	delta;
+    uint8	*old_addr;
 
     FUNC_ENTER(H5O_alloc_extend_chunk, FAIL);
 
@@ -1167,6 +1276,7 @@ H5O_alloc_extend_chunk(H5O_t *oh, intn chunkno, size_t size)
     }
     FUNC_LEAVE(idx);
 }
+
 
 /*-------------------------------------------------------------------------
  * Function:	H5O_alloc_new_chunk
@@ -1339,6 +1449,7 @@ H5O_alloc_new_chunk(H5F_t *f, H5O_t *oh, size_t size)
 
     FUNC_LEAVE(idx);
 }
+
 
 /*-------------------------------------------------------------------------
  * Function:	H5O_alloc
@@ -1360,9 +1471,9 @@ H5O_alloc_new_chunk(H5F_t *f, H5O_t *oh, size_t size)
 static intn
 H5O_alloc(H5F_t *f, H5O_t *oh, const H5O_class_t *type, size_t size)
 {
-    intn		    chunkno;
-    intn		    idx;
-    intn		    null_idx;
+    intn	chunkno;
+    intn	idx;
+    intn	null_idx;
 
     FUNC_ENTER(H5O_alloc, FAIL);
 
@@ -1441,6 +1552,60 @@ H5O_alloc(H5F_t *f, H5O_t *oh, const H5O_class_t *type, size_t size)
     oh->dirty = TRUE;
     FUNC_LEAVE(idx);
 }
+
+
+/*-------------------------------------------------------------------------
+ * Function:	H5O_share
+ *
+ * Purpose:	Writes a message to the global heap.
+ *
+ * Return:	Success:	SUCCEED, and HOBJ describes the global heap
+ *				object.
+ *
+ *		Failure:	FAIL
+ *
+ * Programmer:	Robb Matzke
+ *              Thursday, April  2, 1998
+ *
+ * Modifications:
+ *
+ *-------------------------------------------------------------------------
+ */
+herr_t
+H5O_share (H5F_t *f, const H5O_class_t *type, const void *mesg,
+	   H5HG_t *hobj/*out*/)
+{
+    size_t	size;
+    void	*buf = NULL;
+    herr_t	ret_value = FAIL;
+    
+    FUNC_ENTER (H5O_share, FAIL);
+
+    /* Check args */
+    assert (f);
+    assert (type);
+    assert (mesg);
+    assert (hobj);
+
+    /* Encode the message put it in the global heap */
+    if ((size = (type->raw_size)(f, mesg))>0) {
+	buf = H5MM_xmalloc (size);
+	if ((type->encode)(f, buf, mesg)<0) {
+	    HGOTO_ERROR (H5E_OHDR, H5E_CANTENCODE, FAIL,
+			 "unable to encode message");
+	}
+	if (H5HG_insert (f, size, buf, hobj)<0) {
+	    HGOTO_ERROR (H5E_OHDR, H5E_CANTINIT, FAIL,
+			 "unable to store message in global heap");
+	}
+    }
+    ret_value = SUCCEED;
+
+ done:
+    H5MM_xfree (buf);
+    FUNC_LEAVE (ret_value);
+}
+
 
 /*-------------------------------------------------------------------------
  * Function:	H5O_debug
@@ -1463,12 +1628,14 @@ herr_t
 H5O_debug(H5F_t *f, const haddr_t *addr, FILE * stream, intn indent,
 	  intn fwidth)
 {
-    H5O_t		   *oh = NULL;
-    intn		    i, chunkno;
-    size_t		    mesg_total = 0, chunk_total = 0;
-    int			   *sequence;
-    haddr_t		    tmp_addr;
-    herr_t		    ret_value = FAIL;
+    H5O_t	*oh = NULL;
+    intn	i, chunkno;
+    size_t	mesg_total = 0, chunk_total = 0;
+    int		*sequence;
+    haddr_t	tmp_addr;
+    herr_t	ret_value = FAIL;
+    void	*(*decode)(H5F_t*, const uint8*, H5HG_t*);
+    herr_t      (*debug)(H5F_t*, const void*, FILE*, intn, intn)=NULL;
 
     FUNC_ENTER(H5O_debug, FAIL);
 
@@ -1540,6 +1707,7 @@ H5O_debug(H5F_t *f, const haddr_t *addr, FILE * stream, intn indent,
 		    oh->mesg[i].type->id);
 	    continue;
 	}
+
 	/* message name and size */
 	fprintf(stream, "%*s%-*s 0x%04x %s(%d)\n",
 		indent + 3, "", MAX(0, fwidth - 3),
@@ -1547,12 +1715,20 @@ H5O_debug(H5F_t *f, const haddr_t *addr, FILE * stream, intn indent,
 		(unsigned) (oh->mesg[i].type->id),
 		oh->mesg[i].type->name,
 		sequence[oh->mesg[i].type->id]++);
-	fprintf(stream, "%*s%-*s %lu\n", indent + 3, "", MAX(0, fwidth - 3),
-		"Raw size in bytes:",
-		(unsigned long) (oh->mesg[i].raw_size));
+	fprintf (stream, "%*s%-*s %s\n", indent+3, "", MAX (0, fwidth-3),
+		 "Shared message:",
+		 (oh->mesg[i].flags & H5O_FLAG_SHARED) ? "Yes" : "No");
 	fprintf(stream, "%*s%-*s %s\n", indent + 3, "", MAX(0, fwidth - 3),
 		"Constant:",
-		oh->mesg[i].constant ? "Yes" : "No");
+		(oh->mesg[i].flags & H5O_FLAG_CONSTANT) ? "Yes" : "No");
+	if (oh->mesg[i].flags & ~H5O_FLAG_BITS) {
+	    fprintf (stream, "%*s%-*s 0x%02x\n", indent+3,"",MAX(0,fwidth-3), 
+		     "*** ADDITIONAL UNKNOWN FLAGS --->",
+		     oh->mesg[i].flags & ~H5O_FLAG_BITS);
+	}
+	fprintf(stream, "%*s%-*s %lu bytes\n", indent+3, "", MAX(0,fwidth-3),
+		"Raw size in obj header:",
+		(unsigned long) (oh->mesg[i].raw_size));
 	fprintf(stream, "%*s%-*s %d\n", indent + 3, "", MAX(0, fwidth - 3),
 		"Chunk number:",
 		(int) (oh->mesg[i].chunkno));
@@ -1560,25 +1736,47 @@ H5O_debug(H5F_t *f, const haddr_t *addr, FILE * stream, intn indent,
 	if (chunkno < 0 || chunkno >= oh->nchunks) {
 	    fprintf(stream, "*** BAD CHUNK NUMBER\n");
 	}
+	
 	/* check the size */
 	if ((oh->mesg[i].raw + oh->mesg[i].raw_size >
 	     oh->chunk[chunkno].image + oh->chunk[chunkno].size) ||
 	    (oh->mesg[i].raw < oh->chunk[chunkno].image)) {
 	    fprintf(stream, "*** BAD MESSAGE RAW ADDRESS\n");
 	}
+	
 	/* decode the message */
 	if (NULL == oh->mesg[i].native && oh->mesg[i].type->decode) {
-	    oh->mesg[i].native = (oh->mesg[i].type->decode) (f,
-						       oh->mesg[i].raw_size,
-							   oh->mesg[i].raw);
+	    if (oh->mesg[i].flags & H5O_FLAG_SHARED) {
+		decode = H5O_SHARED->decode;
+		debug = H5O_SHARED->debug;
+	    } else {
+		decode = oh->mesg[i].type->decode;
+		debug = oh->mesg[i].type->debug;
+	    }
+	    oh->mesg[i].native = (decode)(f, oh->mesg[i].raw, NULL);
+	} else {
+	    debug = NULL;
 	}
+	
 	/* print the message */
-	if (oh->mesg[i].type->debug) {
-	    (oh->mesg[i].type->debug)(f, oh->mesg[i].native, stream, indent+3,
-				       MAX(0, fwidth-3));
+	if (debug) {
+	    (debug)(f, oh->mesg[i].native, stream, indent+3, MAX(0, fwidth-3));
 	} else {
 	    fprintf(stream, "%*sNo info for this message.\n", indent + 3, "");
 	}
+
+	/* If the message is shared then also print the pointed-to message */
+	if (oh->mesg[i].flags & H5O_FLAG_SHARED) {
+	    void *p = H5HG_read (f, oh->mesg[i].native, NULL);
+	    void *mesg = (oh->mesg[i].type->decode)(f, p, oh->mesg[i].native);
+	    if (oh->mesg[i].type->debug) {
+		(oh->mesg[i].type->debug)(f, mesg, stream, indent+3,
+					  MAX (0, fwidth-3));
+	    }
+	    H5O_reset (oh->mesg[i].type, mesg);
+	    H5MM_xfree (mesg);
+	    H5MM_xfree (p);
+	}
     }
     sequence = H5MM_xfree(sequence);
 
diff --git a/src/H5Ocont.c b/src/H5Ocont.c
index b3226e2..5d59875 100644
--- a/src/H5Ocont.c
+++ b/src/H5Ocont.c
@@ -25,9 +25,8 @@
 #define PABLO_MASK      H5O_cont_mask
 
 /* PRIVATE PROTOTYPES */
-static void *H5O_cont_decode(H5F_t *f, size_t raw_size, const uint8 *p);
-static herr_t H5O_cont_encode(H5F_t *f, size_t size, uint8 *p,
-                                        const void *_mesg);
+static void *H5O_cont_decode(H5F_t *f, const uint8 *p, H5HG_t *hobj);
+static herr_t H5O_cont_encode(H5F_t *f, uint8 *p, const void *_mesg);
 static herr_t H5O_cont_debug(H5F_t *f, const void *_mesg, FILE * stream,
 			     intn indent, intn fwidth);
 
@@ -41,6 +40,7 @@ const H5O_class_t H5O_CONT[1] = {{
     NULL,                   /*no copy method                */
     NULL,                   /*no size method                */
     NULL,                   /*default reset method          */
+    NULL, 		    /*no share method		    */
     H5O_cont_debug,         /*debugging                     */
 }};
 
@@ -65,8 +65,8 @@ static intn             interface_initialize_g = FALSE;
  *
  *-------------------------------------------------------------------------
  */
-static void            *
-H5O_cont_decode(H5F_t *f, size_t raw_size, const uint8 *p)
+static void *
+H5O_cont_decode(H5F_t *f, const uint8 *p, H5HG_t *hobj)
 {
     H5O_cont_t             *cont = NULL;
 
@@ -74,8 +74,8 @@ H5O_cont_decode(H5F_t *f, size_t raw_size, const uint8 *p)
 
     /* check args */
     assert(f);
-    assert(raw_size == H5O_ALIGN (H5F_SIZEOF_ADDR(f) + H5F_SIZEOF_SIZE(f)));
     assert(p);
+    assert (!hobj || !H5HG_defined (hobj));
 
     /* decode */
     cont = H5MM_xcalloc(1, sizeof(H5O_cont_t));
@@ -103,7 +103,7 @@ H5O_cont_decode(H5F_t *f, size_t raw_size, const uint8 *p)
  *-------------------------------------------------------------------------
  */
 static herr_t
-H5O_cont_encode(H5F_t *f, size_t size, uint8 *p, const void *_mesg)
+H5O_cont_encode(H5F_t *f, uint8 *p, const void *_mesg)
 {
     const H5O_cont_t       *cont = (const H5O_cont_t *) _mesg;
 
@@ -111,7 +111,6 @@ H5O_cont_encode(H5F_t *f, size_t size, uint8 *p, const void *_mesg)
 
     /* check args */
     assert(f);
-    assert(size == H5O_ALIGN (H5F_SIZEOF_ADDR(f) + H5F_SIZEOF_SIZE(f)));
     assert(p);
     assert(cont);
 
diff --git a/src/H5Odtype.c b/src/H5Odtype.c
index fe30d00..c3b46cd 100644
--- a/src/H5Odtype.c
+++ b/src/H5Odtype.c
@@ -28,29 +28,28 @@ static char             RcsId[] = "@(#)$Revision$";
 #define PABLO_MASK      H5O_dtype_mask
 
 /* PRIVATE PROTOTYPES */
-static herr_t           H5O_dtype_encode(H5F_t *f, size_t raw_size, uint8 *p,
-                                         const void *mesg);
-static void            *H5O_dtype_decode(H5F_t *f, size_t raw_size, const uint8 *p);
-static void            *H5O_dtype_copy(const void *_mesg, void *_dest);
-static size_t           H5O_dtype_size(H5F_t *f, const void *_mesg);
-static herr_t           H5O_dtype_reset(void *_mesg);
-static herr_t           H5O_dtype_debug(H5F_t *f, const void *_mesg,
-                                   FILE * stream, intn indent, intn fwidth);
+static herr_t H5O_dtype_encode (H5F_t *f, uint8 *p, const void *mesg);
+static void *H5O_dtype_decode (H5F_t *f, const uint8 *p, H5HG_t *hobj);
+static void *H5O_dtype_copy (const void *_mesg, void *_dest);
+static size_t H5O_dtype_size (H5F_t *f, const void *_mesg);
+static herr_t H5O_dtype_reset (void *_mesg);
+static herr_t H5O_dtype_debug (H5F_t *f, const void *_mesg,
+			       FILE * stream, intn indent, intn fwidth);
+static herr_t H5O_dtype_share (H5F_t *f, const void *_mesg, H5HG_t *hobj);
 
 /* This message derives from H5O */
-const H5O_class_t       H5O_DTYPE[1] =
-{
-    {
-        H5O_DTYPE_ID,           /* message id number            */
-        "data_type",            /* message name for debugging   */
-        sizeof(H5T_t),          /* native message size          */
-        H5O_dtype_decode,       /* decode message               */
-        H5O_dtype_encode,       /* encode message               */
-        H5O_dtype_copy,         /* copy the native value        */
-        H5O_dtype_size,         /* size of raw message          */
-        H5O_dtype_reset,        /* reset method                 */
-        H5O_dtype_debug,        /* debug the message            */
-    }};
+const H5O_class_t H5O_DTYPE[1] = {{
+    H5O_DTYPE_ID,		/* message id number            */
+    "data_type",		/* message name for debugging   */
+    sizeof(H5T_t),		/* native message size          */
+    H5O_dtype_decode,		/* decode message               */
+    H5O_dtype_encode,		/* encode message               */
+    H5O_dtype_copy,		/* copy the native value        */
+    H5O_dtype_size,		/* size of raw message          */
+    H5O_dtype_reset,		/* reset method                 */
+    H5O_dtype_share,		/* share method			*/
+    H5O_dtype_debug,		/* debug the message            */
+}};
 
 /* Interface initialization */
 static hbool_t          interface_initialize_g = FALSE;
@@ -436,8 +435,8 @@ H5O_dtype_encode_helper(uint8 **pp, const H5T_t *dt)
     into a struct in memory native format.  The struct is allocated within this
     function using malloc() and is returned to the caller.
 --------------------------------------------------------------------------*/
-static void            *
-H5O_dtype_decode(H5F_t *f, size_t raw_size, const uint8 *p)
+static void *
+H5O_dtype_decode(H5F_t *f, const uint8 *p, H5HG_t *hobj)
 {
     H5T_t                  *dt = NULL;
 
@@ -445,7 +444,6 @@ H5O_dtype_decode(H5F_t *f, size_t raw_size, const uint8 *p)
 
     /* check args */
     assert(f);
-    assert(raw_size > 0);
     assert(p);
 
     dt = H5MM_xcalloc(1, sizeof(H5T_t));
@@ -455,7 +453,10 @@ H5O_dtype_decode(H5F_t *f, size_t raw_size, const uint8 *p)
         HRETURN_ERROR(H5E_DATATYPE, H5E_CANTDECODE, NULL,
                       "can't decode type");
     }
-    assert(raw_size == H5O_ALIGN (H5O_dtype_size(f, (void *) dt)));
+    if (hobj) {
+	dt->sh_heap = *hobj;
+	dt->sh_file = f;
+    }
 
     FUNC_LEAVE(dt);
 }
@@ -478,7 +479,7 @@ H5O_dtype_decode(H5F_t *f, size_t raw_size, const uint8 *p)
     message in the "raw" disk form.
 --------------------------------------------------------------------------*/
 static herr_t
-H5O_dtype_encode(H5F_t *f, size_t raw_size, uint8 *p, const void *mesg)
+H5O_dtype_encode(H5F_t *f, uint8 *p, const void *mesg)
 {
     const H5T_t            *dt = (const H5T_t *) mesg;
 
@@ -486,7 +487,6 @@ H5O_dtype_encode(H5F_t *f, size_t raw_size, uint8 *p, const void *mesg)
 
     /* check args */
     assert(f);
-    assert(raw_size == H5O_ALIGN (H5O_dtype_size(f, mesg)));
     assert(p);
     assert(dt);
 
@@ -625,6 +625,45 @@ H5O_dtype_reset(void *_mesg)
     FUNC_LEAVE(SUCCEED);
 }
 
+
+/*-------------------------------------------------------------------------
+ * Function:	H5O_dtype_share
+ *
+ * Purpose:	Returns, through argument HOBJ, whether a data type is shared
+ *		in the specified file.
+ *
+ * Return:	Success:	SUCCEED if the data type is shared in file F,
+ *				and HOBJ is set to the global heap address.
+ *
+ *		Failure:	FAIL if the data type is not shared, or
+ *				shared but not in file F.  The value of HOBJ
+ *				is undefined.
+ *
+ * Programmer:	Robb Matzke
+ *              Thursday, April  2, 1998
+ *
+ * Modifications:
+ *
+ *-------------------------------------------------------------------------
+ */
+static herr_t
+H5O_dtype_share (H5F_t *f, const void *_mesg, H5HG_t *hobj/*out*/)
+{
+    const H5T_t		*dt = (const H5T_t *)_mesg;
+    
+    FUNC_ENTER (H5O_dtype_share, FAIL);
+    
+    if (!H5HG_defined (&(dt->sh_heap)) ||
+	NULL==dt->sh_file ||
+	dt->sh_file->shared != f->shared) {
+	HRETURN_ERROR (H5E_DATATYPE, H5E_CANTINIT, FAIL,
+		       "data type is not shared");
+    }
+    
+    *hobj = dt->sh_heap;
+    FUNC_LEAVE (SUCCEED);
+}
+	
 /*--------------------------------------------------------------------------
  NAME
     H5O_dtype_debug
diff --git a/src/H5Oefl.c b/src/H5Oefl.c
index b4bdf19..18dd40d 100644
--- a/src/H5Oefl.c
+++ b/src/H5Oefl.c
@@ -14,9 +14,8 @@
 #define PABLO_MASK	H5O_efl_mask
 
 /* PRIVATE PROTOTYPES */
-static void *H5O_efl_decode(H5F_t *f, size_t raw_size, const uint8 *p);
-static herr_t H5O_efl_encode(H5F_t *f, size_t size, uint8 *p,
-			     const void *_mesg);
+static void *H5O_efl_decode(H5F_t *f, const uint8 *p, H5HG_t *hobj);
+static herr_t H5O_efl_encode(H5F_t *f, uint8 *p, const void *_mesg);
 static void *H5O_efl_copy(const void *_mesg, void *_dest);
 static size_t H5O_efl_size(H5F_t *f, const void *_mesg);
 static herr_t H5O_efl_reset(void *_mesg);
@@ -33,6 +32,7 @@ const H5O_class_t H5O_EFL[1] = {{
     H5O_efl_copy,	    /*copy native value		    */
     H5O_efl_size,	    /*size of message on disk	    */
     H5O_efl_reset,	    /*reset method		    */
+    NULL,	  	    /*no share method		    */
     H5O_efl_debug,	    /*debug the message		    */
 }};
 
@@ -59,7 +59,7 @@ static hbool_t interface_initialize_g = FALSE;
  *-------------------------------------------------------------------------
  */
 static void *
-H5O_efl_decode(H5F_t *f, size_t raw_size, const uint8 *p)
+H5O_efl_decode(H5F_t *f, const uint8 *p, H5HG_t *hobj)
 {
     H5O_efl_t		*mesg = NULL;
     int			i;
@@ -70,6 +70,7 @@ H5O_efl_decode(H5F_t *f, size_t raw_size, const uint8 *p)
     /* Check args */
     assert(f);
     assert(p);
+    assert (!hobj || !H5HG_defined (hobj));
 
     /* Decode the header */
     mesg = H5MM_xcalloc(1, sizeof(H5O_efl_t));
@@ -122,7 +123,7 @@ H5O_efl_decode(H5F_t *f, size_t raw_size, const uint8 *p)
  *-------------------------------------------------------------------------
  */
 static herr_t
-H5O_efl_encode(H5F_t *f, size_t raw_size, uint8 *p, const void *_mesg)
+H5O_efl_encode(H5F_t *f, uint8 *p, const void *_mesg)
 {
     const H5O_efl_t	*mesg = (const H5O_efl_t *)_mesg;
     int			i;
@@ -134,7 +135,6 @@ H5O_efl_encode(H5F_t *f, size_t raw_size, uint8 *p, const void *_mesg)
     /* check args */
     assert(f);
     assert(mesg);
-    assert(raw_size == H5O_ALIGN (H5O_efl_size(f, _mesg)));
     assert(p);
 
     /* Encode header */
diff --git a/src/H5Olayout.c b/src/H5Olayout.c
index 71fe092..7949136 100644
--- a/src/H5Olayout.c
+++ b/src/H5Olayout.c
@@ -14,9 +14,8 @@
 #include <H5Oprivate.h>
 
 /* PRIVATE PROTOTYPES */
-static void *H5O_layout_decode(H5F_t *f, size_t raw_size, const uint8 *p);
-static herr_t H5O_layout_encode(H5F_t *f, size_t size, uint8 *p,
-				const void *_mesg);
+static void *H5O_layout_decode(H5F_t *f, const uint8 *p, H5HG_t *hobj);
+static herr_t H5O_layout_encode(H5F_t *f, uint8 *p, const void *_mesg);
 static void *H5O_layout_copy(const void *_mesg, void *_dest);
 static size_t H5O_layout_size(H5F_t *f, const void *_mesg);
 static herr_t H5O_layout_debug(H5F_t *f, const void *_mesg, FILE * stream,
@@ -32,6 +31,7 @@ const H5O_class_t H5O_LAYOUT[1] = {{
     H5O_layout_copy,        /*copy the native value         */
     H5O_layout_size,        /*size of message on disk       */
     NULL,                   /*reset method                  */
+    NULL,		    /*no share method		    */
     H5O_layout_debug,       /*debug the message             */
 }};
 
@@ -58,8 +58,8 @@ static hbool_t interface_initialize_g = FALSE;
  *
  *-------------------------------------------------------------------------
  */
-static void            *
-H5O_layout_decode(H5F_t *f, size_t raw_size, const uint8 *p)
+static void *
+H5O_layout_decode(H5F_t *f, const uint8 *p, H5HG_t *hobj)
 {
     H5O_layout_t           *mesg = NULL;
     intn                    i;
@@ -69,12 +69,12 @@ H5O_layout_decode(H5F_t *f, size_t raw_size, const uint8 *p)
     /* check args */
     assert(f);
     assert(p);
+    assert (!hobj || !H5HG_defined (hobj));
 
     /* decode */
     mesg = H5MM_xcalloc(1, sizeof(H5O_layout_t));
     H5F_addr_decode(f, &p, &(mesg->addr));
     mesg->ndims = *p++;
-    assert(raw_size == H5O_ALIGN (H5O_layout_size(f, mesg)));
 
     /* Layout class */
     mesg->type = *p++;
@@ -108,7 +108,7 @@ H5O_layout_decode(H5F_t *f, size_t raw_size, const uint8 *p)
  *-------------------------------------------------------------------------
  */
 static herr_t
-H5O_layout_encode(H5F_t *f, size_t raw_size, uint8 *p, const void *_mesg)
+H5O_layout_encode(H5F_t *f, uint8 *p, const void *_mesg)
 {
     const H5O_layout_t     *mesg = (const H5O_layout_t *) _mesg;
     int                     i;
@@ -119,7 +119,6 @@ H5O_layout_encode(H5F_t *f, size_t raw_size, uint8 *p, const void *_mesg)
     assert(f);
     assert(mesg);
     assert(mesg->ndims > 0 && mesg->ndims <= H5O_LAYOUT_NDIMS);
-    assert(raw_size == H5O_ALIGN (H5O_layout_size(f, _mesg)));
     assert(p);
 
     /* data or B-tree address */
diff --git a/src/H5Oname.c b/src/H5Oname.c
index b36c550..cd7e144 100644
--- a/src/H5Oname.c
+++ b/src/H5Oname.c
@@ -22,9 +22,8 @@
 #define PABLO_MASK      H5O_name_mask
 
 /* PRIVATE PROTOTYPES */
-static void *H5O_name_decode(H5F_t *f, size_t raw_size, const uint8 *p);
-static herr_t H5O_name_encode(H5F_t *f, size_t raw_size, uint8 *p,
-			      const void *_mesg);
+static void *H5O_name_decode(H5F_t *f, const uint8 *p, H5HG_t *hobj);
+static herr_t H5O_name_encode(H5F_t *f, uint8 *p, const void *_mesg);
 static void *H5O_name_copy(const void *_mesg, void *_dest);
 static size_t H5O_name_size(H5F_t *f, const void *_mesg);
 static herr_t H5O_name_reset(void *_mesg);
@@ -41,6 +40,7 @@ const H5O_class_t H5O_NAME[1] = {{
     H5O_name_copy,          /*copy the native value         */
     H5O_name_size,          /*raw message size              */
     H5O_name_reset,         /*free internal memory          */
+    NULL,		    /*no share method		    */
     H5O_name_debug,         /*debug the message             */
 }};
 
@@ -67,23 +67,22 @@ static hbool_t interface_initialize_g = FALSE;
  *
  *-------------------------------------------------------------------------
  */
-static void            *
-H5O_name_decode(H5F_t *f, size_t raw_size, const uint8 *p)
+static void *
+H5O_name_decode(H5F_t *f, const uint8 *p, H5HG_t *hobj)
 {
     H5O_name_t             *mesg;
-    char                   *s;
 
     FUNC_ENTER(H5O_name_decode, NULL);
 
     /* check args */
     assert(f);
     assert(p);
+    assert (!hobj || !H5HG_defined (hobj));
 
     /* decode */
     mesg = H5MM_xcalloc(1, sizeof(H5O_name_t));
-    s = H5MM_xmalloc(raw_size);
-    HDmemcpy(s, p, raw_size);
-    mesg->s = s;
+    mesg->s = H5MM_xmalloc (strlen ((const char*)p)+1);
+    strcpy (mesg->s, (const char*)p);
 
     FUNC_LEAVE(mesg);
 }
@@ -106,10 +105,9 @@ H5O_name_decode(H5F_t *f, size_t raw_size, const uint8 *p)
  *-------------------------------------------------------------------------
  */
 static herr_t
-H5O_name_encode(H5F_t *f, size_t raw_size, uint8 *p, const void *_mesg)
+H5O_name_encode(H5F_t *f, uint8 *p, const void *_mesg)
 {
     const H5O_name_t       *mesg = (const H5O_name_t *) _mesg;
-    size_t                  size;
 
     FUNC_ENTER(H5O_name_encode, FAIL);
 
@@ -118,14 +116,8 @@ H5O_name_encode(H5F_t *f, size_t raw_size, uint8 *p, const void *_mesg)
     assert(p);
     assert(mesg && mesg->s);
 
-    /* message size */
-    size = HDstrlen(mesg->s) + 1;
-    assert(size <= raw_size);
-
     /* encode */
-    HDmemcpy(p, mesg->s, size);
-    HDmemset(p + size, 0, raw_size - size);
-
+    strcpy ((char*)p, mesg->s);
     FUNC_LEAVE(SUCCEED);
 }
 
@@ -255,10 +247,10 @@ H5O_name_reset(void *_mesg)
  *-------------------------------------------------------------------------
  */
 static herr_t
-H5O_name_debug(H5F_t *f, const void *_mesg, FILE * stream,
-               intn indent, intn fwidth)
+H5O_name_debug(H5F_t *f, const void *_mesg, FILE *stream, intn indent,
+	       intn fwidth)
 {
-    const H5O_name_t       *mesg = (const H5O_name_t *) _mesg;
+    const H5O_name_t	*mesg = (const H5O_name_t *)_mesg;
 
     FUNC_ENTER(H5O_name_debug, FAIL);
 
diff --git a/src/H5Onull.c b/src/H5Onull.c
index 57cec41..b2b9136 100644
--- a/src/H5Onull.c
+++ b/src/H5Onull.c
@@ -29,5 +29,6 @@ const H5O_class_t H5O_NULL[1] = {{
     NULL,                   /*no copy method                */
     NULL,                   /*no size method                */
     NULL,                   /*no reset method               */
+    NULL,		    /*no share method		    */
     NULL,                   /*no debug method               */
 }};
diff --git a/src/H5Oprivate.h b/src/H5Oprivate.h
index b20e6ed..90317fc 100644
--- a/src/H5Oprivate.h
+++ b/src/H5Oprivate.h
@@ -19,10 +19,11 @@
 
 #include <H5Opublic.h>
 
-/* Private headers neede by this file */
+/* Private headers needed by this file */
 #include <H5private.h>
 #include <H5Fprivate.h>
 #include <H5Gprivate.h>
+#include <H5HGprivate.h>
 #include <H5Tprivate.h>
 #include <H5Sprivate.h>
 
@@ -40,9 +41,10 @@
 #define H5O_NEW_MESG	(-1)		/*new message			     */
 #define H5O_ALL		(-1)		/*delete all messages of type	     */
 
-/* Flags which are part of the message id */
-#define H5O_FLAG_CONSTANT	0x8000
-#define H5O_FLAG_BITS		0x8000
+/* Flags which are part of a message */
+#define H5O_FLAG_CONSTANT	0x01
+#define H5O_FLAG_SHARED		0x02
+#define H5O_FLAG_BITS		0x03
 #define H5O_VERSION		1
 
 /*
@@ -64,21 +66,22 @@
 	       4)	/*reserved		*/
 
 typedef struct H5O_class_t {
-    intn	id;				    /*message type ID on disk*/
-    const char	*name;				 /*message name for debugging*/
-    size_t	native_size;			     /*size of native message*/
-    void	*(*decode) (H5F_t *, size_t, const uint8 *);
-    herr_t	(*encode) (H5F_t *, size_t, uint8 *, const void *);
-    void	*(*copy) (const void *, void *);     /*copy native value     */
-    size_t	(*raw_size) (H5F_t *, const void *); /*sizeof raw val	     */
-    herr_t	(*reset) (void *);		/*free nested data structures*/
-    herr_t	(*debug) (H5F_t *, const void *, FILE *, intn, intn);
+    intn	id;				 /*message type ID on disk   */
+    const char	*name;				 /*for debugging             */
+    size_t	native_size;			 /*size of native message    */
+    void	*(*decode)(H5F_t*, const uint8*, H5HG_t*);
+    herr_t	(*encode)(H5F_t*, uint8*, const void*);
+    void	*(*copy)(const void*, void*);    /*copy native value         */
+    size_t	(*raw_size)(H5F_t*, const void*);/*sizeof raw val	     */
+    herr_t	(*reset)(void *);		 /*free nested data structs  */
+    herr_t	(*share)(H5F_t*, const void*, H5HG_t*);
+    herr_t	(*debug)(H5F_t*, const void*, FILE*, intn, intn);
 } H5O_class_t;
 
 typedef struct H5O_mesg_t {
     const H5O_class_t	*type;		/*type of message		     */
     hbool_t		dirty;		/*raw out of date wrt native	     */
-    hbool_t		constant;	/*is message constant?		     */
+    uint8		flags;		/*message flags			     */
     void		*native;	/*native format message		     */
     uint8		*raw;		/*ptr to raw data		     */
     size_t		raw_size;	/*size with alignment		     */
@@ -169,10 +172,20 @@ typedef struct H5O_layout_t {
 extern const H5O_class_t H5O_NAME[1];
 
 typedef struct H5O_name_t {
-    const char	*s;			/*ptr to malloc'd memory	     */
+    char	*s;			/*ptr to malloc'd memory	     */
 } H5O_name_t;
 
 /*
+ * Shared object message.  This message ID never really appears in an object
+ * header.  Instead, bit 2 of the `Flags' field will be set and the ID field
+ * will be the ID of the pointed-to message.
+ */
+#define H5O_SHARED_ID	0x000f
+extern const H5O_class_t H5O_SHARED[1];
+
+typedef H5HG_t H5O_shared_t;
+
+/*
  * Object header continuation message.
  */
 #define H5O_CONT_ID	0x0010
@@ -211,6 +224,8 @@ intn H5O_modify (H5G_entry_t *ent, const H5O_class_t *type, intn overwrite,
 		 uintn flags, const void *mesg);
 herr_t H5O_remove (H5G_entry_t *ent, const H5O_class_t *type, intn sequence);
 herr_t H5O_reset (const H5O_class_t *type, void *native);
+herr_t H5O_share (H5F_t *f, const H5O_class_t *type, const void *mesg,
+		  H5HG_t *hobj/*out*/);
 herr_t H5O_debug (H5F_t *f, const haddr_t *addr, FILE * stream, intn indent,
 		  intn fwidth);
 
diff --git a/src/H5Osdspace.c b/src/H5Osdspace.c
index 9818130..21d8f3c 100644
--- a/src/H5Osdspace.c
+++ b/src/H5Osdspace.c
@@ -25,9 +25,8 @@ static char             RcsId[] = "@(#)$Revision$";
 #define PABLO_MASK      H5O_sdspace_mask
 
 /* PRIVATE PROTOTYPES */
-static void *H5O_sdspace_decode(H5F_t *f, size_t raw_size, const uint8 *p);
-static herr_t H5O_sdspace_encode(H5F_t *f, size_t size, uint8 *p,
-				 const void *_mesg);
+static void *H5O_sdspace_decode(H5F_t *f, const uint8 *p, H5HG_t *hobj);
+static herr_t H5O_sdspace_encode(H5F_t *f, uint8 *p, const void *_mesg);
 static void *H5O_sdspace_copy(const void *_mesg, void *_dest);
 static size_t H5O_sdspace_size(H5F_t *f, const void *_mesg);
 static herr_t H5O_sdspace_debug(H5F_t *f, const void *_mesg,
@@ -43,6 +42,7 @@ const H5O_class_t H5O_SDSPACE[1] = {{
     H5O_sdspace_copy,       /* copy the native value                */
     H5O_sdspace_size,       /* size of symbol table entry           */
     NULL,                   /* default reset method                 */
+    NULL,		    /* no share method 			    */
     H5O_sdspace_debug,      /* debug the message                    */
 }};
 
@@ -69,7 +69,7 @@ static hbool_t interface_initialize_g = FALSE;
     within this function using malloc() and is returned to the caller.
 --------------------------------------------------------------------------*/
 static void *
-H5O_sdspace_decode(H5F_t *f, size_t raw_size, const uint8 *p)
+H5O_sdspace_decode(H5F_t *f, const uint8 *p, H5HG_t *hobj)
 {
     H5S_simple_t	*sdim = NULL;/* New simple dimensionality structure */
     uintn               u;  		/* local counting variable */
@@ -79,8 +79,8 @@ H5O_sdspace_decode(H5F_t *f, size_t raw_size, const uint8 *p)
 
     /* check args */
     assert(f);
-    assert(raw_size >= 8); /* at least the rank and flags must be present */
     assert(p);
+    assert (!hobj || !H5HG_defined (hobj));
 
     /* decode */
     if ((sdim = H5MM_xcalloc(1, sizeof(H5S_simple_t))) != NULL) {
@@ -131,7 +131,7 @@ H5O_sdspace_decode(H5F_t *f, size_t raw_size, const uint8 *p)
     dimensionality message in the "raw" disk form.
 --------------------------------------------------------------------------*/
 static herr_t
-H5O_sdspace_encode(H5F_t *f, size_t raw_size, uint8 *p, const void *mesg)
+H5O_sdspace_encode(H5F_t *f, uint8 *p, const void *mesg)
 {
     const H5S_simple_t  *sdim = (const H5S_simple_t *) mesg;
     uintn               u;  /* Local counting variable */
@@ -141,7 +141,6 @@ H5O_sdspace_encode(H5F_t *f, size_t raw_size, uint8 *p, const void *mesg)
 
     /* check args */
     assert(f);
-    assert(raw_size >= 8);      /* at least the rank & flags must be present */
     assert(p);
     assert(sdim);
 
diff --git a/src/H5Oshared.c b/src/H5Oshared.c
new file mode 100644
index 0000000..a62a562
--- /dev/null
+++ b/src/H5Oshared.c
@@ -0,0 +1,184 @@
+/*
+ * Copyright (C) 1998 NCSA
+ *		      All rights reserved.
+ *
+ * Programmer:	Robb Matzke <matzke@llnl.gov>
+ *		Wednesday, April  1, 1998
+ *
+ * Purpose:	Functions that operate on a shared message.  The shared
+ *		message doesn't ever actually appear in the object header as
+ *		a normal message.  Instead, if a message is shared, the
+ *		H5O_FLAG_SHARED bit is set and the message body is that
+ *		defined here for H5O_SHARED.  The message ID is the ID of the
+ *		pointed-to message and the pointed-to message is stored in
+ *		the global heap.
+ */
+#include <H5private.h>
+#include <H5Eprivate.h>
+#include <H5MMprivate.h>
+#include <H5Oprivate.h>
+
+static void *H5O_shared_decode (H5F_t*, const uint8*, H5HG_t *hobj);
+static herr_t H5O_shared_encode (H5F_t*, uint8*, const void*);
+static size_t H5O_shared_size (H5F_t*, const void*);
+static herr_t H5O_shared_debug (H5F_t*, const void*, FILE*, intn, intn);
+
+/* This message derives from H5O */
+const H5O_class_t H5O_SHARED[1] = {{
+    H5O_SHARED_ID,	    	/*message id number			*/
+    "shared",		    	/*message name for debugging		*/
+    sizeof(H5O_shared_t), 	/*native message size			*/
+    H5O_shared_decode,	    	/*decode method				*/
+    H5O_shared_encode,	    	/*encode method				*/
+    NULL,		    	/*no copy method			*/
+    H5O_shared_size,	    	/*size method				*/
+    NULL,		    	/*no reset method			*/
+    NULL,			/*no share method			*/
+    H5O_shared_debug,	    	/*debug method				*/
+}};
+
+/* Interface initialization */
+#define PABLO_MASK	H5O_shared_mask
+static hbool_t interface_initialize_g = FALSE;
+#define INTERFACE_INIT  NULL
+
+
+/*-------------------------------------------------------------------------
+ * Function:	H5O_shared_decode
+ *
+ * Purpose:	Decodes a shared object message and returns it.
+ *
+ * Return:	Success:	Ptr to a new shared object message.
+ *
+ *		Failure:	NULL
+ *
+ * Programmer:	Robb Matzke
+ *              Thursday, April  2, 1998
+ *
+ * Modifications:
+ *
+ *-------------------------------------------------------------------------
+ */
+static void *
+H5O_shared_decode (H5F_t *f, const uint8 *buf, H5HG_t *hobj)
+{
+    H5O_shared_t	*mesg;
+    
+    FUNC_ENTER (H5O_shared_decode, NULL);
+
+    /* Check args */
+    assert (f);
+    assert (buf);
+    assert (!hobj || !H5HG_defined (hobj));
+
+    /* Decode */
+    mesg = H5MM_xcalloc (1, sizeof *mesg);
+    H5F_addr_decode (f, &buf, &(mesg->addr));
+    INT32DECODE (buf, mesg->idx);
+
+    FUNC_LEAVE (mesg);
+}
+
+
+/*-------------------------------------------------------------------------
+ * Function:	H5O_shared_encode
+ *
+ * Purpose:	Encodes message _MESG into buffer BUF.
+ *
+ * Return:	Success:	SUCCEED
+ *
+ *		Failure:	FAIL
+ *
+ * Programmer:	Robb Matzke
+ *              Thursday, April  2, 1998
+ *
+ * Modifications:
+ *
+ *-------------------------------------------------------------------------
+ */
+static herr_t
+H5O_shared_encode (H5F_t *f, uint8 *buf/*out*/, const void *_mesg)
+{
+    const H5O_shared_t	*mesg = (const H5O_shared_t *)_mesg;
+    
+    FUNC_ENTER (H5O_shared_encode, FAIL);
+
+    /* Check args */
+    assert (f);
+    assert (buf);
+    assert (mesg);
+
+    /* Encode */
+    H5F_addr_encode (f, &buf, &(mesg->addr));
+    INT32ENCODE (buf, mesg->idx);
+
+    FUNC_LEAVE (SUCCEED);
+}
+
+
+/*-------------------------------------------------------------------------
+ * Function:	H5O_shared_size
+ *
+ * Purpose:	Returns the length of a shared object message.
+ *
+ * Return:	Success:	Length
+ *
+ *		Failure:	0
+ *
+ * Programmer:	Robb Matzke
+ *              Thursday, April  2, 1998
+ *
+ * Modifications:
+ *
+ *-------------------------------------------------------------------------
+ */
+static size_t
+H5O_shared_size (H5F_t *f, const void *_mesg)
+{
+    FUNC_ENTER (H5O_shared_size, 0);
+    FUNC_LEAVE (H5F_SIZEOF_ADDR(f)+4);
+}
+
+
+/*-------------------------------------------------------------------------
+ * Function:	H5O_shared_debug
+ *
+ * Purpose:	Prints debugging info for the message
+ *
+ * Return:	Success:	SUCCEED
+ *
+ *		Failure:	FAIL
+ *
+ * Programmer:	Robb Matzke
+ *              Thursday, April  2, 1998
+ *
+ * Modifications:
+ *
+ *-------------------------------------------------------------------------
+ */
+static herr_t
+H5O_shared_debug (H5F_t *f, const void *_mesg, FILE *stream, intn indent,
+		  intn fwidth)
+{
+    const H5O_shared_t	*mesg = (const H5O_shared_t *)_mesg;
+
+    FUNC_ENTER (H5O_shared_debug, FAIL);
+
+    /* Check args */
+    assert (f);
+    assert (mesg);
+    assert (stream);
+    assert (indent>=0);
+    assert (fwidth>=0);
+
+    fprintf (stream, "%*s%-*s ", indent, "", fwidth,
+	     "Collection address:");
+    H5F_addr_print (stream, &(mesg->addr));
+    fprintf (stream, "\n");
+
+    fprintf (stream, "%*s%-*s %d\n", indent, "", fwidth,
+	     "Object ID within collection:",
+	     mesg->idx);
+
+    FUNC_LEAVE (SUCCEED);
+}
diff --git a/src/H5Ostab.c b/src/H5Ostab.c
index 56d3955..a5b0dc7 100644
--- a/src/H5Ostab.c
+++ b/src/H5Ostab.c
@@ -23,9 +23,8 @@
 #define PABLO_MASK      H5O_stab_mask
 
 /* PRIVATE PROTOTYPES */
-static void *H5O_stab_decode(H5F_t *f, size_t raw_size, const uint8 *p);
-static herr_t H5O_stab_encode(H5F_t *f, size_t size, uint8 *p,
-			      const void *_mesg);
+static void *H5O_stab_decode(H5F_t *f, const uint8 *p, H5HG_t *hobj);
+static herr_t H5O_stab_encode(H5F_t *f, uint8 *p, const void *_mesg);
 static void *H5O_stab_copy(const void *_mesg, void *_dest);
 static size_t H5O_stab_size(H5F_t *f, const void *_mesg);
 static herr_t H5O_stab_debug(H5F_t *f, const void *_mesg,
@@ -41,6 +40,7 @@ const H5O_class_t H5O_STAB[1] = {{
     H5O_stab_copy,          /*copy the native value         */
     H5O_stab_size,          /*size of symbol table entry    */
     NULL,                   /*default reset method          */
+    NULL,		    /*no share method		    */
     H5O_stab_debug,         /*debug the message             */
 }};
 
@@ -67,7 +67,7 @@ static hbool_t interface_initialize_g = FALSE;
  *-------------------------------------------------------------------------
  */
 static void *
-H5O_stab_decode(H5F_t *f, size_t raw_size, const uint8 *p)
+H5O_stab_decode(H5F_t *f, const uint8 *p, H5HG_t *hobj)
 {
     H5O_stab_t             *stab;
 
@@ -75,8 +75,8 @@ H5O_stab_decode(H5F_t *f, size_t raw_size, const uint8 *p)
 
     /* check args */
     assert(f);
-    assert(raw_size == H5O_ALIGN (2 * H5F_SIZEOF_ADDR(f)));
     assert(p);
+    assert (!hobj || !H5HG_defined (hobj));
 
     /* decode */
     stab = H5MM_xcalloc(1, sizeof(H5O_stab_t));
@@ -104,7 +104,7 @@ H5O_stab_decode(H5F_t *f, size_t raw_size, const uint8 *p)
  *-------------------------------------------------------------------------
  */
 static herr_t
-H5O_stab_encode(H5F_t *f, size_t raw_size, uint8 *p, const void *_mesg)
+H5O_stab_encode(H5F_t *f, uint8 *p, const void *_mesg)
 {
     const H5O_stab_t       *stab = (const H5O_stab_t *) _mesg;
 
@@ -112,7 +112,6 @@ H5O_stab_encode(H5F_t *f, size_t raw_size, uint8 *p, const void *_mesg)
 
     /* check args */
     assert(f);
-    assert(raw_size == H5O_ALIGN (2 * H5F_SIZEOF_ADDR(f)));
     assert(p);
     assert(stab);
 
diff --git a/src/H5T.c b/src/H5T.c
index fe23b04..be72fa6 100644
--- a/src/H5T.c
+++ b/src/H5T.c
@@ -1,16 +1,10 @@
 /*
- * 
-* NCSA HDF								   *
-* Software Development Group						   *
-* National Center for Supercomputing Applications			   *
-* University of Illinois at Urbana-Champaign				   *
-* 605 E. Springfield, Champaign IL 61820				   *
-*									   *
-* For conditions of distribution and use, see the accompanying		   *
-* hdf/COPYING file.							   *
-*									   *
-****************************************************************************/
-
+ * Copyright (C) 1998 NCSA
+ *		      All rights reserved.
+ *
+ * Programmer:	Robb Matzke <matzke@llnl.gov>
+ *		Tuesday, March 31, 1998
+ */
 #ifdef RCSID
 static char		RcsId[] = "@(#)$Revision$";
 #endif
@@ -19,7 +13,8 @@ static char		RcsId[] = "@(#)$Revision$";
 
 #include <H5private.h>		/*generic functions			  */
 #include <H5Iprivate.h>		/*ID functions		  */
-#include <H5Eprivate.h>		/*error handling		  */
+#include <H5Eprivate.h>		/*error handling			 */
+#include <H5HGprivate.h>	/*global heap				  */
 #include <H5MMprivate.h>	/*memory management			  */
 #include <H5Sprivate.h>		/*data space				  */
 #include <H5Tpkg.h>		/*data-type functions			  */
@@ -29,47 +24,47 @@ static char		RcsId[] = "@(#)$Revision$";
 #define H5T_COMPND_INC	64	/*typical max numb of members per struct */
 
 /* Interface initialization */
-static intn		interface_initialize_g = FALSE;
+static intn interface_initialize_g = FALSE;
 #define INTERFACE_INIT H5T_init_interface
-static void		H5T_term_interface(void);
+static void H5T_term_interface(void);
 
 /* Predefined types */
-hid_t			H5T_NATIVE_CHAR_g = FAIL;
-hid_t			H5T_NATIVE_UCHAR_g = FAIL;
-hid_t			H5T_NATIVE_SHORT_g = FAIL;
-hid_t			H5T_NATIVE_USHORT_g = FAIL;
-hid_t			H5T_NATIVE_INT_g = FAIL;
-hid_t			H5T_NATIVE_UINT_g = FAIL;
-hid_t			H5T_NATIVE_LONG_g = FAIL;
-hid_t			H5T_NATIVE_LLONG_g = FAIL;
-hid_t			H5T_NATIVE_ULLONG_g = FAIL;
-hid_t			H5T_NATIVE_HYPER_g = FAIL;
-hid_t			H5T_NATIVE_UHYPER_g = FAIL;
-hid_t			H5T_NATIVE_INT8_g = FAIL;
-hid_t			H5T_NATIVE_UINT8_g = FAIL;
-hid_t			H5T_NATIVE_INT16_g = FAIL;
-hid_t			H5T_NATIVE_UINT16_g = FAIL;
-hid_t			H5T_NATIVE_INT32_g = FAIL;
-hid_t			H5T_NATIVE_UINT32_g = FAIL;
-hid_t			H5T_NATIVE_INT64_g = FAIL;
-hid_t			H5T_NATIVE_UINT64_g = FAIL;
-hid_t			H5T_NATIVE_ULONG_g = FAIL;
-hid_t			H5T_NATIVE_FLOAT_g = FAIL;
-hid_t			H5T_NATIVE_DOUBLE_g = FAIL;
-hid_t			H5T_NATIVE_TIME_g = FAIL;
-hid_t			H5T_NATIVE_STRING_g = FAIL;
-hid_t			H5T_NATIVE_BITFIELD_g = FAIL;
-hid_t			H5T_NATIVE_OPAQUE_g = FAIL;
+hid_t H5T_NATIVE_CHAR_g = FAIL;
+hid_t H5T_NATIVE_UCHAR_g = FAIL;
+hid_t H5T_NATIVE_SHORT_g = FAIL;
+hid_t H5T_NATIVE_USHORT_g = FAIL;
+hid_t H5T_NATIVE_INT_g = FAIL;
+hid_t H5T_NATIVE_UINT_g = FAIL;
+hid_t H5T_NATIVE_LONG_g = FAIL;
+hid_t H5T_NATIVE_LLONG_g = FAIL;
+hid_t H5T_NATIVE_ULLONG_g = FAIL;
+hid_t H5T_NATIVE_HYPER_g = FAIL;
+hid_t H5T_NATIVE_UHYPER_g = FAIL;
+hid_t H5T_NATIVE_INT8_g = FAIL;
+hid_t H5T_NATIVE_UINT8_g = FAIL;
+hid_t H5T_NATIVE_INT16_g = FAIL;
+hid_t H5T_NATIVE_UINT16_g = FAIL;
+hid_t H5T_NATIVE_INT32_g = FAIL;
+hid_t H5T_NATIVE_UINT32_g = FAIL;
+hid_t H5T_NATIVE_INT64_g = FAIL;
+hid_t H5T_NATIVE_UINT64_g = FAIL;
+hid_t H5T_NATIVE_ULONG_g = FAIL;
+hid_t H5T_NATIVE_FLOAT_g = FAIL;
+hid_t H5T_NATIVE_DOUBLE_g = FAIL;
+hid_t H5T_NATIVE_TIME_g = FAIL;
+hid_t H5T_NATIVE_STRING_g = FAIL;
+hid_t H5T_NATIVE_BITFIELD_g = FAIL;
+hid_t H5T_NATIVE_OPAQUE_g = FAIL;
 
 /* The path database */
-static intn		H5T_npath_g = 0;	/*num paths defined	*/
-static intn		H5T_apath_g = 0;	/*num slots allocated	*/
-static H5T_path_t      *H5T_path_g = NULL;	/*path array		*/
+static intn H5T_npath_g = 0;			/*num paths defined	*/
+static intn H5T_apath_g = 0;			/*num slots allocated	*/
+static H5T_path_t *H5T_path_g = NULL;		/*path array		*/
 
 /* The soft conversion function master list */
-static intn		H5T_nsoft_g = 0;	/*num soft funcs defined */
-static intn		H5T_asoft_g = 0;	/*num slots allocated	*/
-static H5T_soft_t      *H5T_soft_g = NULL;	/*master soft list	*/
+static intn H5T_nsoft_g = 0;			/*num soft funcs defined */
+static intn H5T_asoft_g = 0;			/*num slots allocated	*/
+static H5T_soft_t *H5T_soft_g = NULL;		/*master soft list	*/
 
 /*--------------------------------------------------------------------------
 NAME
@@ -86,8 +81,8 @@ DESCRIPTION
 herr_t
 H5T_init_interface(void)
 {
-    H5T_t		   *dt = NULL;
-    herr_t		    ret_value = SUCCEED;
+    H5T_t	*dt = NULL;
+    herr_t	ret_value = SUCCEED;
 
     interface_initialize_g = TRUE;
     FUNC_ENTER(H5T_init_interface, FAIL);
@@ -285,7 +280,7 @@ H5T_term_interface(void)
 	    path->cdata.command = H5T_CONV_FREE;
 	    if ((path->func)(FAIL, FAIL, &(path->cdata), 0, NULL, NULL)<0) {
 #ifdef H5T_DEBUG
-		fprintf (stderr, "HDF5-DIAG: conversion function failed "
+		fprintf (stderr, "H5T: conversion function failed "
 			 "to free private data\n");
 #endif
 		H5E_clear(); /*ignore the error*/
@@ -336,6 +331,7 @@ H5T_term_interface(void)
     H5T_NATIVE_BITFIELD_g = FAIL;
     H5T_NATIVE_OPAQUE_g = FAIL;
 }
+
 
 /*-------------------------------------------------------------------------
  * Function:	H5Tcreate
@@ -362,8 +358,8 @@ H5T_term_interface(void)
 hid_t
 H5Tcreate(H5T_class_t type, size_t size)
 {
-    H5T_t		   *dt = NULL;
-    hid_t		    ret_value = FAIL;
+    H5T_t	*dt = NULL;
+    hid_t	ret_value = FAIL;
 
     FUNC_ENTER(H5Tcreate, FAIL);
 
@@ -371,17 +367,21 @@ H5Tcreate(H5T_class_t type, size_t size)
     if (size <= 0) {
 	HRETURN_ERROR(H5E_ARGS, H5E_BADVALUE, FAIL, "invalid size");
     }
+
     /* create the type */
     if (NULL == (dt = H5T_create(type, size))) {
 	HRETURN_ERROR(H5E_DATATYPE, H5E_CANTINIT, FAIL, "can't create type");
     }
+
     /* Make it an atom */
     if ((ret_value = H5I_register(H5_DATATYPE, dt)) < 0) {
 	HRETURN_ERROR(H5E_DATATYPE, H5E_CANTREGISTER, FAIL,
 		      "can't register data type atom");
     }
+
     FUNC_LEAVE(ret_value);
 }
+
 
 /*-------------------------------------------------------------------------
  * Function:	H5Tcopy
@@ -404,9 +404,9 @@ H5Tcreate(H5T_class_t type, size_t size)
 hid_t
 H5Tcopy(hid_t type_id)
 {
-    H5T_t		   *dt = NULL;
-    H5T_t		   *new_dt = NULL;
-    hid_t		    ret_value = FAIL;
+    H5T_t	*dt = NULL;
+    H5T_t	*new_dt = NULL;
+    hid_t	ret_value = FAIL;
 
     FUNC_ENTER(H5Tcopy, FAIL);
 
@@ -420,14 +420,17 @@ H5Tcopy(hid_t type_id)
     if (NULL == (new_dt = H5T_copy(dt))) {
 	HRETURN_ERROR(H5E_DATATYPE, H5E_CANTINIT, FAIL, "can't copy");
     }
-    /* atomize result */
+
+    /* Atomize result */
     if ((ret_value = H5I_register(H5_DATATYPE, new_dt)) < 0) {
 	H5T_close(new_dt);
 	HRETURN_ERROR(H5E_DATATYPE, H5E_CANTREGISTER, FAIL,
 		      "can't register data type atom");
     }
+    
     FUNC_LEAVE(ret_value);
 }
+
 
 /*-------------------------------------------------------------------------
  * Function:	H5Tclose
@@ -448,7 +451,7 @@ H5Tcopy(hid_t type_id)
 herr_t
 H5Tclose(hid_t type_id)
 {
-    H5T_t		   *dt = NULL;
+    H5T_t	*dt = NULL;
 
     FUNC_ENTER(H5Tclose, FAIL);
 
@@ -460,12 +463,15 @@ H5Tclose(hid_t type_id)
     if (dt->locked) {
 	HRETURN_ERROR(H5E_ARGS, H5E_BADVALUE, FAIL, "predefined data type");
     }
+
     /* When the reference count reaches zero the resources are freed */
     if (H5I_dec_ref(type_id) < 0) {
 	HRETURN_ERROR(H5E_ATOM, H5E_BADATOM, FAIL, "problem freeing id");
     }
+    
     FUNC_LEAVE(SUCCEED);
 }
+
 
 /*-------------------------------------------------------------------------
  * Function:	H5Tequal
@@ -488,9 +494,9 @@ H5Tclose(hid_t type_id)
 hbool_t
 H5Tequal(hid_t type1_id, hid_t type2_id)
 {
-    const H5T_t		   *dt1 = NULL;
-    const H5T_t		   *dt2 = NULL;
-    hbool_t		    ret_value = FAIL;
+    const H5T_t		*dt1 = NULL;
+    const H5T_t		*dt2 = NULL;
+    hbool_t		ret_value = FAIL;
 
     FUNC_ENTER(H5Tequal, FAIL);
 
@@ -505,6 +511,7 @@ H5Tequal(hid_t type1_id, hid_t type2_id)
 
     FUNC_LEAVE(ret_value);
 }
+
 
 /*-------------------------------------------------------------------------
  * Function:	H5Tlock
@@ -530,7 +537,7 @@ H5Tequal(hid_t type1_id, hid_t type2_id)
 herr_t
 H5Tlock(hid_t type_id)
 {
-    H5T_t		   *dt = NULL;
+    H5T_t	*dt = NULL;
 
     FUNC_ENTER(H5Tlock, FAIL);
 
@@ -540,8 +547,10 @@ H5Tlock(hid_t type_id)
 	HRETURN_ERROR(H5E_ARGS, H5E_BADTYPE, FAIL, "not a data type");
     }
     dt->locked = TRUE;
+    
     FUNC_LEAVE(SUCCEED);
 }
+
 
 /*-------------------------------------------------------------------------
  * Function:	H5Tget_class
@@ -563,7 +572,7 @@ H5Tlock(hid_t type_id)
 H5T_class_t
 H5Tget_class(hid_t type_id)
 {
-    H5T_t		   *dt = NULL;
+    H5T_t	*dt = NULL;
 
     FUNC_ENTER(H5Tget_class, H5T_NO_CLASS);
 
@@ -572,8 +581,10 @@ H5Tget_class(hid_t type_id)
 	NULL == (dt = H5I_object(type_id))) {
 	HRETURN_ERROR(H5E_ARGS, H5E_BADTYPE, H5T_NO_CLASS, "not a data type");
     }
+    
     FUNC_LEAVE(dt->type);
 }
+
 
 /*-------------------------------------------------------------------------
  * Function:	H5Tget_size
@@ -596,8 +607,8 @@ H5Tget_class(hid_t type_id)
 size_t
 H5Tget_size(hid_t type_id)
 {
-    H5T_t		   *dt = NULL;
-    size_t		    size;
+    H5T_t	*dt = NULL;
+    size_t	size;
 
     FUNC_ENTER(H5Tget_size, 0);
 
@@ -606,11 +617,13 @@ H5Tget_size(hid_t type_id)
 	NULL == (dt = H5I_object(type_id))) {
 	HRETURN_ERROR(H5E_ARGS, H5E_BADTYPE, 0, "not a data type");
     }
+    
     /* size */
     size = H5T_get_size(dt);
 
     FUNC_LEAVE(size);
 }
+
 
 /*-------------------------------------------------------------------------
  * Function:	H5Tset_size
@@ -643,8 +656,8 @@ H5Tget_size(hid_t type_id)
 herr_t
 H5Tset_size(hid_t type_id, size_t size)
 {
-    H5T_t		   *dt = NULL;
-    size_t		    prec, offset;
+    H5T_t	*dt = NULL;
+    size_t	prec, offset;
 
     FUNC_ENTER(H5Tset_size, FAIL);
 
@@ -713,12 +726,14 @@ H5Tset_size(hid_t type_id, size_t size)
     }
 
     /* Commit */
+    H5T_unshare (dt);
     dt->size = size;
     dt->u.atomic.offset = offset;
     dt->u.atomic.prec = prec;
 
     FUNC_LEAVE(SUCCEED);
 }
+
 
 /*-------------------------------------------------------------------------
  * Function:	H5Tget_order
@@ -739,8 +754,8 @@ H5Tset_size(hid_t type_id, size_t size)
 H5T_order_t
 H5Tget_order(hid_t type_id)
 {
-    H5T_t		   *dt = NULL;
-    H5T_order_t		    order;
+    H5T_t		*dt = NULL;
+    H5T_order_t		order;
 
     FUNC_ENTER(H5Tget_order, H5T_ORDER_ERROR);
 
@@ -751,11 +766,13 @@ H5Tget_order(hid_t type_id)
 	HRETURN_ERROR(H5E_ARGS, H5E_BADTYPE, H5T_ORDER_ERROR,
 		      "not an atomic data type");
     }
-    /* order */
+
+    /* Order */
     order = dt->u.atomic.order;
 
     FUNC_LEAVE(order);
 }
+
 
 /*-------------------------------------------------------------------------
  * Function:	H5Tset_order
@@ -776,7 +793,7 @@ H5Tget_order(hid_t type_id)
 herr_t
 H5Tset_order(hid_t type_id, H5T_order_t order)
 {
-    H5T_t		   *dt = NULL;
+    H5T_t	*dt = NULL;
 
     FUNC_ENTER(H5Tset_order, FAIL);
 
@@ -792,10 +809,13 @@ H5Tset_order(hid_t type_id, H5T_order_t order)
     if (order < 0 || order > H5T_ORDER_NONE) {
 	HRETURN_ERROR(H5E_ARGS, H5E_BADVALUE, FAIL, "illegal byte order");
     }
-    /* order */
+
+    /* Commit */
+    H5T_unshare (dt);
     dt->u.atomic.order = order;
     FUNC_LEAVE(SUCCEED);
 }
+
 
 /*-------------------------------------------------------------------------
  * Function:	H5Tget_precision
@@ -820,8 +840,8 @@ H5Tset_order(hid_t type_id, H5T_order_t order)
 size_t
 H5Tget_precision(hid_t type_id)
 {
-    H5T_t		   *dt = NULL;
-    size_t		    prec;
+    H5T_t	*dt = NULL;
+    size_t	prec;
 
     FUNC_ENTER(H5Tget_precision, 0);
 
@@ -831,11 +851,13 @@ H5Tget_precision(hid_t type_id)
 	!H5T_is_atomic(dt)) {
 	HRETURN_ERROR(H5E_ARGS, H5E_BADTYPE, 0, "not an atomic data type");
     }
-    /* precision */
+    
+    /* Precision */
     prec = dt->u.atomic.prec;
 
     FUNC_LEAVE(prec);
 }
+
 
 /*-------------------------------------------------------------------------
  * Function:	H5Tset_precision
@@ -870,8 +892,8 @@ H5Tget_precision(hid_t type_id)
 herr_t
 H5Tset_precision(hid_t type_id, size_t prec)
 {
-    H5T_t		   *dt = NULL;
-    size_t		    offset, size;
+    H5T_t	*dt = NULL;
+    size_t	offset, size;
 
     FUNC_ENTER(H5Tset_prec, FAIL);
 
@@ -888,6 +910,7 @@ H5Tset_precision(hid_t type_id, size_t prec)
 	HRETURN_ERROR(H5E_ARGS, H5E_BADVALUE, FAIL,
 		      "precision must be positive");
     }
+    
     /* Adjust the offset and size */
     offset = dt->u.atomic.offset;
     size = dt->size;
@@ -934,12 +957,14 @@ H5Tset_precision(hid_t type_id, size_t prec)
     }
 
     /* Commit */
+    H5T_unshare (dt);
     dt->size = size;
     dt->u.atomic.offset = offset;
     dt->u.atomic.prec = prec;
 
     FUNC_LEAVE(SUCCEED);
 }
+
 
 /*-------------------------------------------------------------------------
  * Function:	H5Tget_offset
@@ -976,8 +1001,8 @@ H5Tset_precision(hid_t type_id, size_t prec)
 size_t
 H5Tget_offset(hid_t type_id)
 {
-    H5T_t		   *dt = NULL;
-    size_t		    offset;
+    H5T_t	*dt = NULL;
+    size_t	offset;
 
     FUNC_ENTER(H5Tget_offset, 0);
 
@@ -987,11 +1012,13 @@ H5Tget_offset(hid_t type_id)
 	!H5T_is_atomic(dt)) {
 	HRETURN_ERROR(H5E_ARGS, H5E_BADTYPE, 0, "not an atomic data type");
     }
-    /* offset */
+    
+    /* Offset */
     offset = dt->u.atomic.offset;
 
     FUNC_LEAVE(offset);
 }
+
 
 /*-------------------------------------------------------------------------
  * Function:	H5Tset_offset
@@ -1035,7 +1062,7 @@ H5Tget_offset(hid_t type_id)
 herr_t
 H5Tset_offset(hid_t type_id, size_t offset)
 {
-    H5T_t		   *dt = NULL;
+    H5T_t	*dt = NULL;
 
     FUNC_ENTER(H5Tset_offset, FAIL);
 
@@ -1052,15 +1079,19 @@ H5Tset_offset(hid_t type_id, size_t offset)
 	HRETURN_ERROR(H5E_ARGS, H5E_BADVALUE, FAIL,
 		      "offset must be zero for this type");
     }
+    
     /* Adjust the size */
     if (offset + dt->u.atomic.prec > 8 * dt->size) {
 	dt->size = (offset + dt->u.atomic.prec + 7) / 8;
     }
+    
     /* Commit */
+    H5T_unshare (dt);
     dt->u.atomic.offset = offset;
 
     FUNC_LEAVE(SUCCEED);
 }
+
 
 /*-------------------------------------------------------------------------
  * Function:	H5Tget_pad
@@ -1081,9 +1112,9 @@ H5Tset_offset(hid_t type_id, size_t offset)
  *-------------------------------------------------------------------------
  */
 herr_t
-H5Tget_pad(hid_t type_id, H5T_pad_t *lsb /*out */ , H5T_pad_t *msb /*out */ )
+H5Tget_pad(hid_t type_id, H5T_pad_t *lsb/*out*/, H5T_pad_t *msb/*out*/)
 {
-    H5T_t		   *dt = NULL;
+    H5T_t	*dt = NULL;
 
     FUNC_ENTER(H5Tget_pad, FAIL);
 
@@ -1093,14 +1124,14 @@ H5Tget_pad(hid_t type_id, H5T_pad_t *lsb /*out */ , H5T_pad_t *msb /*out */ )
 	!H5T_is_atomic(dt)) {
 	HRETURN_ERROR(H5E_ARGS, H5E_BADTYPE, FAIL, "not an atomic data type");
     }
+    
     /* Get values */
-    if (lsb)
-	*lsb = dt->u.atomic.lsb_pad;
-    if (msb)
-	*msb = dt->u.atomic.msb_pad;
+    if (lsb) *lsb = dt->u.atomic.lsb_pad;
+    if (msb) *msb = dt->u.atomic.msb_pad;
 
     FUNC_LEAVE(SUCCEED);
 }
+
 
 /*-------------------------------------------------------------------------
  * Function:	H5Tset_pad
@@ -1121,7 +1152,7 @@ H5Tget_pad(hid_t type_id, H5T_pad_t *lsb /*out */ , H5T_pad_t *msb /*out */ )
 herr_t
 H5Tset_pad(hid_t type_id, H5T_pad_t lsb, H5T_pad_t msb)
 {
-    H5T_t		   *dt = NULL;
+    H5T_t *dt = NULL;
 
     FUNC_ENTER(H5Tset_pad, FAIL);
 
@@ -1137,11 +1168,15 @@ H5Tset_pad(hid_t type_id, H5T_pad_t lsb, H5T_pad_t msb)
     if (lsb < 0 || lsb >= H5T_NPAD || msb < 0 || msb >= H5T_NPAD) {
 	HRETURN_ERROR(H5E_ARGS, H5E_BADVALUE, FAIL, "invalid pad type");
     }
+
+    /* Commit */
+    H5T_unshare (dt);
     dt->u.atomic.lsb_pad = lsb;
     dt->u.atomic.msb_pad = msb;
 
     FUNC_LEAVE(SUCCEED);
 }
+
 
 /*-------------------------------------------------------------------------
  * Function:	H5Tget_sign
@@ -1162,8 +1197,8 @@ H5Tset_pad(hid_t type_id, H5T_pad_t lsb, H5T_pad_t msb)
 H5T_sign_t
 H5Tget_sign(hid_t type_id)
 {
-    H5T_t		   *dt = NULL;
-    H5T_sign_t		    sign;
+    H5T_t		*dt = NULL;
+    H5T_sign_t		sign;
 
     FUNC_ENTER(H5Tget_sign, H5T_SGN_ERROR);
 
@@ -1174,11 +1209,13 @@ H5Tget_sign(hid_t type_id)
 	HRETURN_ERROR(H5E_ARGS, H5E_BADTYPE, H5T_SGN_ERROR,
 		      "not an integer data type");
     }
-    /* sign */
+    
+    /* Sign */
     sign = dt->u.atomic.u.i.sign;
 
     FUNC_LEAVE(sign);
 }
+
 
 /*-------------------------------------------------------------------------
  * Function:	H5Tset_sign
@@ -1199,7 +1236,7 @@ H5Tget_sign(hid_t type_id)
 herr_t
 H5Tset_sign(hid_t type_id, H5T_sign_t sign)
 {
-    H5T_t		   *dt = NULL;
+    H5T_t	*dt = NULL;
 
     FUNC_ENTER(H5Tset_sign, FAIL);
 
@@ -1215,10 +1252,13 @@ H5Tset_sign(hid_t type_id, H5T_sign_t sign)
     if (sign < 0 || sign >= H5T_NSGN) {
 	HRETURN_ERROR(H5E_ARGS, H5E_BADVALUE, FAIL, "illegal sign type");
     }
-    /* sign */
+    
+    /* Commit */
+    H5T_unshare (dt);
     dt->u.atomic.u.i.sign = sign;
     FUNC_LEAVE(SUCCEED);
 }
+
 
 /*-------------------------------------------------------------------------
  * Function:	H5Tget_fields
@@ -1243,11 +1283,11 @@ H5Tset_sign(hid_t type_id, H5T_sign_t sign)
  *-------------------------------------------------------------------------
  */
 herr_t
-H5Tget_fields(hid_t type_id, size_t *spos /*out */ ,
-	      size_t *epos /*out */ , size_t *esize /*out */ ,
-	      size_t *mpos /*out */ , size_t *msize /*out */ )
+H5Tget_fields(hid_t type_id, size_t *spos/*out*/,
+	      size_t *epos/*out*/, size_t *esize/*out*/,
+	      size_t *mpos/*out*/, size_t *msize/*out*/)
 {
-    H5T_t		   *dt = NULL;
+    H5T_t	*dt = NULL;
 
     FUNC_ENTER(H5Tget_fields, FAIL);
 
@@ -1258,20 +1298,17 @@ H5Tget_fields(hid_t type_id, size_t *spos /*out */ ,
 	HRETURN_ERROR(H5E_ARGS, H5E_BADTYPE, FAIL,
 		      "not a floating-point data type");
     }
+    
     /* Get values */
-    if (spos)
-	*spos = dt->u.atomic.u.f.sign;
-    if (epos)
-	*epos = dt->u.atomic.u.f.epos;
-    if (esize)
-	*esize = dt->u.atomic.u.f.esize;
-    if (mpos)
-	*mpos = dt->u.atomic.u.f.mpos;
-    if (msize)
-	*msize = dt->u.atomic.u.f.msize;
+    if (spos) *spos = dt->u.atomic.u.f.sign;
+    if (epos) *epos = dt->u.atomic.u.f.epos;
+    if (esize) *esize = dt->u.atomic.u.f.esize;
+    if (mpos) *mpos = dt->u.atomic.u.f.mpos;
+    if (msize) *msize = dt->u.atomic.u.f.msize;
 
     FUNC_LEAVE(SUCCEED);
 }
+
 
 /*-------------------------------------------------------------------------
  * Function:	H5Tset_fields
@@ -1299,7 +1336,7 @@ herr_t
 H5Tset_fields(hid_t type_id, size_t spos, size_t epos, size_t esize,
 	      size_t mpos, size_t msize)
 {
-    H5T_t		   *dt = NULL;
+    H5T_t	*dt = NULL;
 
     FUNC_ENTER(H5Tset_fields, FAIL);
 
@@ -1325,6 +1362,7 @@ H5Tset_fields(hid_t type_id, size_t spos, size_t epos, size_t esize,
 	HRETURN_ERROR(H5E_ARGS, H5E_BADVALUE, FAIL,
 		      "sign location is not valid");
     }
+    
     /* Check for overlap */
     if (spos >= epos && spos < epos + esize) {
 	HRETURN_ERROR(H5E_ARGS, H5E_BADVALUE, FAIL,
@@ -1339,7 +1377,9 @@ H5Tset_fields(hid_t type_id, size_t spos, size_t epos, size_t esize,
 	HRETURN_ERROR(H5E_ARGS, H5E_BADVALUE, FAIL,
 		      "exponent and mantissa fields overlap");
     }
+    
     /* Commit */
+    H5T_unshare (dt);
     dt->u.atomic.u.f.sign = spos;
     dt->u.atomic.u.f.epos = epos;
     dt->u.atomic.u.f.mpos = mpos;
@@ -1348,6 +1388,7 @@ H5Tset_fields(hid_t type_id, size_t spos, size_t epos, size_t esize,
 
     FUNC_LEAVE(SUCCEED);
 }
+
 
 /*-------------------------------------------------------------------------
  * Function:	H5Tget_ebias
@@ -1368,8 +1409,8 @@ H5Tset_fields(hid_t type_id, size_t spos, size_t epos, size_t esize,
 size_t
 H5Tget_ebias(hid_t type_id)
 {
-    H5T_t		   *dt = NULL;
-    size_t		    ebias;
+    H5T_t	*dt = NULL;
+    size_t	ebias;
 
     FUNC_ENTER(H5Tget_ebias, 0);
 
@@ -1380,11 +1421,13 @@ H5Tget_ebias(hid_t type_id)
 	HRETURN_ERROR(H5E_ARGS, H5E_BADTYPE, 0,
 		      "not a floating-point data type");
     }
+    
     /* bias */
     ebias = dt->u.atomic.u.f.ebias;
 
     FUNC_LEAVE(ebias);
 }
+
 
 /*-------------------------------------------------------------------------
  * Function:	H5Tset_ebias
@@ -1405,7 +1448,7 @@ H5Tget_ebias(hid_t type_id)
 herr_t
 H5Tset_ebias(hid_t type_id, size_t ebias)
 {
-    H5T_t		   *dt = NULL;
+    H5T_t	*dt = NULL;
 
     FUNC_ENTER(H5Tset_ebias, FAIL);
 
@@ -1419,10 +1462,14 @@ H5Tset_ebias(hid_t type_id, size_t ebias)
     if (dt->locked) {
 	HRETURN_ERROR(H5E_ARGS, H5E_CANTINIT, FAIL, "data type is read-only");
     }
+
+    /* Commit */
+    H5T_unshare (dt);
     dt->u.atomic.u.f.ebias = ebias;
 
     FUNC_LEAVE(SUCCEED);
 }
+
 
 /*-------------------------------------------------------------------------
  * Function:	H5Tget_norm
@@ -1444,8 +1491,8 @@ H5Tset_ebias(hid_t type_id, size_t ebias)
 H5T_norm_t
 H5Tget_norm(hid_t type_id)
 {
-    H5T_t		   *dt = NULL;
-    H5T_norm_t		    norm;
+    H5T_t	*dt = NULL;
+    H5T_norm_t	norm;
 
     FUNC_ENTER(H5Tget_norm, H5T_NORM_ERROR);
 
@@ -1456,11 +1503,13 @@ H5Tget_norm(hid_t type_id)
 	HRETURN_ERROR(H5E_ARGS, H5E_BADTYPE, H5T_NORM_ERROR,
 		      "not a floating-point data type");
     }
+    
     /* norm */
     norm = dt->u.atomic.u.f.norm;
 
     FUNC_LEAVE(norm);
 }
+
 
 /*-------------------------------------------------------------------------
  * Function:	H5Tset_norm
@@ -1482,7 +1531,7 @@ H5Tget_norm(hid_t type_id)
 herr_t
 H5Tset_norm(hid_t type_id, H5T_norm_t norm)
 {
-    H5T_t		   *dt = NULL;
+    H5T_t	*dt = NULL;
 
     FUNC_ENTER(H5Tset_norm, FAIL);
 
@@ -1499,10 +1548,13 @@ H5Tset_norm(hid_t type_id, H5T_norm_t norm)
     if (norm < 0 || norm > H5T_NORM_NONE) {
 	HRETURN_ERROR(H5E_ARGS, H5E_BADVALUE, FAIL, "illegal normalization");
     }
-    /* norm */
+    
+    /* Commit */
+    H5T_unshare (dt);
     dt->u.atomic.u.f.norm = norm;
     FUNC_LEAVE(SUCCEED);
 }
+
 
 /*-------------------------------------------------------------------------
  * Function:	H5Tget_inpad
@@ -1526,8 +1578,8 @@ H5Tset_norm(hid_t type_id, H5T_norm_t norm)
 H5T_pad_t
 H5Tget_inpad(hid_t type_id)
 {
-    H5T_t		   *dt = NULL;
-    H5T_pad_t		    pad;
+    H5T_t	*dt = NULL;
+    H5T_pad_t	pad;
 
     FUNC_ENTER(H5Tget_inpad, H5T_PAD_ERROR);
 
@@ -1538,11 +1590,13 @@ H5Tget_inpad(hid_t type_id)
 	HRETURN_ERROR(H5E_ARGS, H5E_BADTYPE, H5T_PAD_ERROR,
 		      "not a floating-point data type");
     }
+    
     /* pad */
     pad = dt->u.atomic.u.f.pad;
 
     FUNC_LEAVE(pad);
 }
+
 
 /*-------------------------------------------------------------------------
  * Function:	H5Tset_inpad
@@ -1566,7 +1620,7 @@ H5Tget_inpad(hid_t type_id)
 herr_t
 H5Tset_inpad(hid_t type_id, H5T_pad_t pad)
 {
-    H5T_t		   *dt = NULL;
+    H5T_t	*dt = NULL;
 
     FUNC_ENTER(H5Tset_inpad, FAIL);
 
@@ -1584,10 +1638,13 @@ H5Tset_inpad(hid_t type_id, H5T_pad_t pad)
 	HRETURN_ERROR(H5E_ARGS, H5E_BADVALUE, FAIL,
 		      "illegal internal pad type");
     }
-    /* pad */
+    
+    /* Commit */
+    H5T_unshare (dt);
     dt->u.atomic.u.f.pad = pad;
     FUNC_LEAVE(SUCCEED);
 }
+
 
 /*-------------------------------------------------------------------------
  * Function:	H5Tget_cset
@@ -1610,8 +1667,8 @@ H5Tset_inpad(hid_t type_id, H5T_pad_t pad)
 H5T_cset_t
 H5Tget_cset(hid_t type_id)
 {
-    H5T_t		   *dt = NULL;
-    H5T_cset_t		    cset;
+    H5T_t	*dt = NULL;
+    H5T_cset_t	cset;
 
     FUNC_ENTER(H5Tget_cset, H5T_CSET_ERROR);
 
@@ -1622,11 +1679,13 @@ H5Tget_cset(hid_t type_id)
 	HRETURN_ERROR(H5E_ARGS, H5E_BADTYPE, H5T_CSET_ERROR,
 		      "not a string data type");
     }
+    
     /* result */
     cset = dt->u.atomic.u.s.cset;
 
     FUNC_LEAVE(cset);
 }
+
 
 /*-------------------------------------------------------------------------
  * Function:	H5Tset_cset
@@ -1649,7 +1708,7 @@ H5Tget_cset(hid_t type_id)
 herr_t
 H5Tset_cset(hid_t type_id, H5T_cset_t cset)
 {
-    H5T_t		   *dt = NULL;
+    H5T_t	*dt = NULL;
 
     FUNC_ENTER(H5Tset_cset, FAIL);
 
@@ -1666,10 +1725,13 @@ H5Tset_cset(hid_t type_id, H5T_cset_t cset)
 	HRETURN_ERROR(H5E_ARGS, H5E_BADVALUE, FAIL,
 		      "illegal character set type");
     }
-    /* set */
+    
+    /* Commit */
+    H5T_unshare (dt);
     dt->u.atomic.u.s.cset = cset;
     FUNC_LEAVE(SUCCEED);
 }
+
 
 /*-------------------------------------------------------------------------
  * Function:	H5Tget_strpad
@@ -1693,8 +1755,8 @@ H5Tset_cset(hid_t type_id, H5T_cset_t cset)
 H5T_str_t
 H5Tget_strpad(hid_t type_id)
 {
-    H5T_t		   *dt = NULL;
-    H5T_str_t		    strpad;
+    H5T_t	*dt = NULL;
+    H5T_str_t	strpad;
 
     FUNC_ENTER(H5Tget_strpad, H5T_STR_ERROR);
 
@@ -1705,11 +1767,13 @@ H5Tget_strpad(hid_t type_id)
 	HRETURN_ERROR(H5E_ARGS, H5E_BADTYPE, H5T_STR_ERROR,
 		      "not a string data type");
     }
+    
     /* result */
     strpad = dt->u.atomic.u.s.pad;
 
     FUNC_LEAVE(strpad);
 }
+
 
 /*-------------------------------------------------------------------------
  * Function:	H5Tset_strpad
@@ -1733,7 +1797,7 @@ H5Tget_strpad(hid_t type_id)
 herr_t
 H5Tset_strpad(hid_t type_id, H5T_str_t strpad)
 {
-    H5T_t		   *dt = NULL;
+    H5T_t	*dt = NULL;
 
     FUNC_ENTER(H5Tset_strpad, FAIL);
 
@@ -1749,10 +1813,13 @@ H5Tset_strpad(hid_t type_id, H5T_str_t strpad)
     if (strpad < 0 || strpad >= H5T_NSTR) {
 	HRETURN_ERROR(H5E_ARGS, H5E_BADVALUE, FAIL, "illegal string pad type");
     }
-    /* set */
+    
+    /* Commit */
+    H5T_unshare (dt);
     dt->u.atomic.u.s.pad = strpad;
     FUNC_LEAVE(SUCCEED);
 }
+
 
 /*-------------------------------------------------------------------------
  * Function:	H5Tget_nmembers
@@ -1777,7 +1844,7 @@ int
 H5Tget_nmembers(hid_t type_id)
 {
 
-    H5T_t		   *dt = NULL;
+    H5T_t	*dt = NULL;
 
     FUNC_ENTER(H5Tget_num_members, FAIL);
 
@@ -1787,8 +1854,10 @@ H5Tget_nmembers(hid_t type_id)
 	H5T_COMPOUND != dt->type) {
 	HRETURN_ERROR(H5E_ARGS, H5E_BADTYPE, FAIL, "not a compound data type");
     }
+    
     FUNC_LEAVE(dt->u.compnd.nmembs);
 }
+
 
 /*-------------------------------------------------------------------------
  * Function:	H5Tget_member_name
@@ -1813,8 +1882,8 @@ H5Tget_nmembers(hid_t type_id)
 char *
 H5Tget_member_name(hid_t type_id, int membno)
 {
-    H5T_t		   *dt = NULL;
-    char		   *s = NULL;
+    H5T_t	*dt = NULL;
+    char	*s = NULL;
 
     FUNC_ENTER(H5Tget_member_name, NULL);
 
@@ -1827,9 +1896,12 @@ H5Tget_member_name(hid_t type_id, int membno)
     if (membno < 0 || membno >= dt->u.compnd.nmembs) {
 	HRETURN_ERROR(H5E_ARGS, H5E_BADVALUE, NULL, "invalid member number");
     }
+
+    /* Value */
     s = H5MM_xstrdup(dt->u.compnd.memb[membno].name);
     FUNC_LEAVE(s);
 }
+
 
 /*-------------------------------------------------------------------------
  * Function:	H5Tget_member_offset
@@ -1854,8 +1926,8 @@ H5Tget_member_name(hid_t type_id, int membno)
 size_t
 H5Tget_member_offset(hid_t type_id, int membno)
 {
-    H5T_t		   *dt = NULL;
-    size_t		    offset = 0;
+    H5T_t	*dt = NULL;
+    size_t	offset = 0;
 
     FUNC_ENTER(H5Tget_member_offset, 0);
 
@@ -1868,9 +1940,13 @@ H5Tget_member_offset(hid_t type_id, int membno)
     if (membno < 0 || membno >= dt->u.compnd.nmembs) {
 	HRETURN_ERROR(H5E_ARGS, H5E_BADVALUE, 0, "invalid member number");
     }
+
+    /* Value */
     offset = dt->u.compnd.memb[membno].offset;
+
     FUNC_LEAVE(offset);
 }
+
 
 /*-------------------------------------------------------------------------
  * Function:	H5Tget_member_dims
@@ -1895,8 +1971,8 @@ int
 H5Tget_member_dims(hid_t type_id, int membno,
 		   size_t dims[]/*out*/, int perm[]/*out*/)
 {
-    H5T_t		   *dt = NULL;
-    intn		    ndims, i;
+    H5T_t	*dt = NULL;
+    intn	ndims, i;
 
     FUNC_ENTER(H5Tget_member_dims, FAIL);
 
@@ -1909,16 +1985,17 @@ H5Tget_member_dims(hid_t type_id, int membno,
     if (membno < 0 || membno >= dt->u.compnd.nmembs) {
 	HRETURN_ERROR(H5E_ARGS, H5E_BADVALUE, FAIL, "invalid member number");
     }
+
+    /* Value */
     ndims = dt->u.compnd.memb[membno].ndims;
     for (i = 0; i < ndims; i++) {
-	if (dims[i])
-	    dims[i] = dt->u.compnd.memb[membno].dim[i];
-	if (perm[i])
-	    perm[i] = dt->u.compnd.memb[membno].perm[i];
+	if (dims[i]) dims[i] = dt->u.compnd.memb[membno].dim[i];
+	if (perm[i]) perm[i] = dt->u.compnd.memb[membno].perm[i];
     }
 
     FUNC_LEAVE(ndims);
 }
+
 
 /*-------------------------------------------------------------------------
  * Function:	H5Tget_member_type
@@ -1943,8 +2020,8 @@ H5Tget_member_dims(hid_t type_id, int membno,
 hid_t
 H5Tget_member_type(hid_t type_id, int membno)
 {
-    H5T_t		   *dt = NULL, *memb_dt = NULL;
-    hid_t		    memb_type_id;
+    H5T_t	*dt = NULL, *memb_dt = NULL;
+    hid_t	memb_type_id;
 
     FUNC_ENTER(H5Tget_member_type, FAIL);
 
@@ -1957,6 +2034,7 @@ H5Tget_member_type(hid_t type_id, int membno)
     if (membno < 0 || membno >= dt->u.compnd.nmembs) {
 	HRETURN_ERROR(H5E_ARGS, H5E_BADVALUE, FAIL, "invalid member number");
     }
+    
     /* Copy data type into an atom */
     if (NULL == (memb_dt = H5T_copy(dt->u.compnd.memb[membno].type))) {
 	HRETURN_ERROR(H5E_DATATYPE, H5E_CANTINIT, FAIL,
@@ -1967,8 +2045,10 @@ H5Tget_member_type(hid_t type_id, int membno)
 	HRETURN_ERROR(H5E_DATATYPE, H5E_CANTREGISTER, FAIL,
 		      "can't register data type atom");
     }
+    
     FUNC_LEAVE(memb_type_id);
 }
+
 
 /*-------------------------------------------------------------------------
  * Function:	H5Tinsert
@@ -2001,8 +2081,8 @@ H5Tget_member_type(hid_t type_id, int membno)
 herr_t
 H5Tinsert(hid_t parent_id, const char *name, off_t offset, hid_t member_id)
 {
-    H5T_t		   *parent = NULL;	/*the compound parent data type */
-    H5T_t		   *member = NULL;	/*the atomic member type	*/
+    H5T_t	*parent = NULL;		/*the compound parent data type */
+    H5T_t	*member = NULL;		/*the atomic member type	*/
 
     FUNC_ENTER(H5Tinsert, FAIL);
 
@@ -2022,12 +2102,16 @@ H5Tinsert(hid_t parent_id, const char *name, off_t offset, hid_t member_id)
 	NULL == (member = H5I_object(member_id))) {
 	HRETURN_ERROR(H5E_ARGS, H5E_BADTYPE, FAIL, "not a data type");
     }
+
+    /* Insert */
     if (H5T_insert(parent, name, offset, member) < 0) {
 	HRETURN_ERROR(H5E_DATATYPE, H5E_CANTINSERT, FAIL,
 		      "can't insert member");
     }
+    
     FUNC_LEAVE(SUCCEED);
 }
+
 
 /*-------------------------------------------------------------------------
  * Function:	H5Tpack
@@ -2049,7 +2133,7 @@ H5Tinsert(hid_t parent_id, const char *name, off_t offset, hid_t member_id)
 herr_t
 H5Tpack(hid_t type_id)
 {
-    H5T_t		   *dt = NULL;
+    H5T_t	*dt = NULL;
 
     FUNC_ENTER(H5Tpack, FAIL);
 
@@ -2062,12 +2146,64 @@ H5Tpack(hid_t type_id)
     if (dt->locked) {
 	HRETURN_ERROR(H5E_ARGS, H5E_BADVALUE, FAIL, "data type is read-only");
     }
+
+    /* Pack */
     if (H5T_pack(dt) < 0) {
 	HRETURN_ERROR(H5E_DATATYPE, H5E_CANTINIT, FAIL,
 		      "unable to pack compound data type");
     }
+    
     FUNC_LEAVE(SUCCEED);
 }
+
+
+/*-------------------------------------------------------------------------
+ * Function:	H5Tshare
+ *
+ * Purpose:	Marks a data type as sharable.  Using the type during the
+ *		creation of a dataset will cause the dataset object header to
+ *		point to the type in the global heap instead of containing
+ *		the type directly in its object header.  Subsequent
+ *		modifications to a shared type cause the type to become
+ *		unshared.
+ *
+ * Return:	Success:	SUCCEED
+ *
+ *		Failure:	FAIL
+ *
+ * Programmer:	Robb Matzke
+ *              Tuesday, March 31, 1998
+ *
+ * Modifications:
+ *
+ *-------------------------------------------------------------------------
+ */
+herr_t
+H5Tshare (hid_t loc_id, hid_t type_id)
+{
+    H5G_t	*loc = NULL;
+    H5T_t	*dt = NULL;
+    
+    FUNC_ENTER (H5Tshare, FAIL);
+
+    /* Check arguments */
+    if (NULL==(loc=H5G_loc (loc_id))) {
+	HRETURN_ERROR (H5E_ARGS, H5E_BADTYPE, FAIL, "not a location");
+    }
+    if (H5_DATATYPE!=H5I_group (type_id) ||
+	NULL==(dt=H5I_object (type_id))) {
+	HRETURN_ERROR (H5E_ARGS, H5E_BADTYPE, FAIL, "not a data type");
+    }
+
+    /* Make it sharable */
+    if (H5T_share (H5G_fileof (loc), dt)<0) {
+	HRETURN_ERROR (H5E_DATATYPE, H5E_CANTINIT, FAIL,
+		       "unable to make data type sharable");
+    }
+
+    FUNC_LEAVE (SUCCEED);
+}
+
 
 /*-------------------------------------------------------------------------
  * Function:	H5Tregister_hard
@@ -2217,7 +2353,7 @@ H5Tregister_soft(H5T_class_t src_cls, H5T_class_t dst_cls, H5T_conv_t func)
 		if ((path->func)(src_id, dst_id, &(path->cdata),
 				 0, NULL, NULL)<0) {
 #ifdef H5T_DEBUG
-		    fprintf (stderr, "HDF5-DIAG: conversion function failed "
+		    fprintf (stderr, "H5T: conversion function failed "
 			     "to free private data.\n");
 #endif
 		    H5E_clear();
@@ -2289,7 +2425,7 @@ H5Tunregister(H5T_conv_t func)
 	    path->cdata.command = H5T_CONV_FREE;
 	    if ((func)(FAIL, FAIL, &(path->cdata), 0, NULL, NULL)<0) {
 #ifdef H5T_DEBUG
-		fprintf (stderr, "HDF5-DIAG: conversion function failed to "
+		fprintf (stderr, "H5T: conversion function failed to "
 			 "free private data.\n");
 #endif
 		H5E_clear();
@@ -2364,8 +2500,8 @@ H5Tunregister(H5T_conv_t func)
 H5T_conv_t
 H5Tfind(hid_t src_id, hid_t dst_id, H5T_cdata_t **pcdata)
 {
-    H5T_conv_t		    ret_value = NULL;
-    H5T_t		   *src = NULL, *dst = NULL;
+    H5T_conv_t	ret_value = NULL;
+    H5T_t	*src = NULL, *dst = NULL;
 
     FUNC_ENTER(H5Tfind, NULL);
 
@@ -2387,6 +2523,7 @@ H5Tfind(hid_t src_id, hid_t dst_id, H5T_cdata_t **pcdata)
 	HRETURN_ERROR(H5E_DATATYPE, H5E_NOTFOUND, NULL,
 		      "conversion function not found");
     }
+    
     FUNC_LEAVE(ret_value);
 }
 
@@ -2413,10 +2550,10 @@ H5Tfind(hid_t src_id, hid_t dst_id, H5T_cdata_t **pcdata)
  *
  *-------------------------------------------------------------------------
  */
-H5T_t		       *
+H5T_t *
 H5T_create(H5T_class_t type, size_t size)
 {
-    H5T_t		   *dt = NULL;
+    H5T_t	*dt = NULL;
 
     FUNC_ENTER(H5T_create, NULL);
 
@@ -2445,6 +2582,7 @@ H5T_create(H5T_class_t type, size_t size)
     dt->size = size;
     FUNC_LEAVE(dt);
 }
+
 
 /*-------------------------------------------------------------------------
  * Function:	H5T_copy
@@ -2466,9 +2604,9 @@ H5T_create(H5T_class_t type, size_t size)
 H5T_t *
 H5T_copy(const H5T_t *old_dt)
 {
-    H5T_t		   *new_dt=NULL, *tmp=NULL;
-    intn		    i;
-    char		   *s;
+    H5T_t	*new_dt=NULL, *tmp=NULL;
+    intn	i;
+    char	*s;
 
     FUNC_ENTER(H5T_copy, NULL);
 
@@ -2498,8 +2636,10 @@ H5T_copy(const H5T_t *old_dt)
 	    new_dt->u.compnd.memb[i].type = tmp;
 	}
     }
+    
     FUNC_LEAVE(new_dt);
 }
+
 
 /*-------------------------------------------------------------------------
  * Function:	H5T_close
@@ -2542,6 +2682,93 @@ H5T_close(H5T_t *dt)
     
     FUNC_LEAVE(SUCCEED);
 }
+
+
+/*-------------------------------------------------------------------------
+ * Function:	H5T_share
+ *
+ * Purpose:	Causes a data type to be marked as sharable.  If the data
+ *		type isn't already marked sharable in the specified file then
+ *		it is written to the global heap of that file and the heap
+ *		location information is added to the sh_file and sh_heap
+ *		fields of the data type.
+ *
+ * Return:	Success:	SUCCEED
+ *
+ *		Failure:	FAIL
+ *
+ * Programmer:	Robb Matzke
+ *              Tuesday, March 31, 1998
+ *
+ * Modifications:
+ *
+ *-------------------------------------------------------------------------
+ */
+herr_t
+H5T_share (H5F_t *f, H5T_t *dt)
+{
+    FUNC_ENTER (H5T_share, FAIL);
+    
+    /* Check args */
+    assert (f);
+    assert (dt);
+
+    /*
+     * If the type is sharable in some other file then unshare it first. A
+     * type can only be sharable in one file at a time.
+     */
+    if (H5HG_defined (&(dt->sh_heap)) && f->shared!=dt->sh_file->shared) {
+	H5T_unshare (dt);
+	H5E_clear (); /*don't really care if it fails*/
+    }
+
+    /*
+     * Write the message to the global heap if it isn't already shared in
+     * this file.
+     */
+    if (!H5HG_defined (&(dt->sh_heap))) {
+	if (H5O_share (f, H5O_DTYPE, dt, &(dt->sh_heap))<0) {
+	    HRETURN_ERROR (H5E_DATATYPE, H5E_CANTINIT, FAIL,
+			   "unable to store data type message in global heap");
+	}
+	dt->sh_file = f;
+    }
+    
+    FUNC_LEAVE (SUCCEED);
+}
+
+
+/*-------------------------------------------------------------------------
+ * Function:	H5T_unshare
+ *
+ * Purpose:	If a data type is in the global heap then this function
+ *		removes that information from the H5T_t struct.
+ *
+ * Return:	Success:	SUCCEED
+ *
+ *		Failure:	FAIL
+ *
+ * Programmer:	Robb Matzke
+ *              Tuesday, March 31, 1998
+ *
+ * Modifications:
+ *
+ *-------------------------------------------------------------------------
+ */
+herr_t
+H5T_unshare (H5T_t *dt)
+{
+    FUNC_ENTER (H5T_unshare, FAIL);
+
+    /* Check args */
+    assert (dt);
+
+    H5HG_undef (&(dt->sh_heap));
+    dt->sh_file = NULL;
+
+    FUNC_LEAVE (SUCCEED);
+}
+
 
 /*-------------------------------------------------------------------------
  * Function:	H5T_is_atomic
@@ -2568,6 +2795,7 @@ H5T_is_atomic(const H5T_t *dt)
 
     FUNC_LEAVE(H5T_COMPOUND == dt->type ? FALSE : TRUE);
 }
+
 
 /*-------------------------------------------------------------------------
  * Function:	H5T_get_size
@@ -2597,6 +2825,7 @@ H5T_get_size(const H5T_t *dt)
 
     FUNC_LEAVE(dt->size);
 }
+
 
 /*-------------------------------------------------------------------------
  * Function:	H5T_insert
@@ -2659,6 +2888,7 @@ H5T_insert(H5T_t *parent, const char *name, off_t offset, const H5T_t *member)
     }
 
     /* Add member to end of member array */
+    H5T_unshare (parent);
     i = parent->u.compnd.nmembs;
     parent->u.compnd.memb[i].name = H5MM_xstrdup(name);
     parent->u.compnd.memb[i].offset = offset;
@@ -2668,6 +2898,7 @@ H5T_insert(H5T_t *parent, const char *name, off_t offset, const H5T_t *member)
     parent->u.compnd.nmembs++;
     FUNC_LEAVE(SUCCEED);
 }
+
 
 /*-------------------------------------------------------------------------
  * Function:	H5T_pack
@@ -2689,14 +2920,15 @@ H5T_insert(H5T_t *parent, const char *name, off_t offset, const H5T_t *member)
 herr_t
 H5T_pack(H5T_t *dt)
 {
-    int			    i;
-    size_t		    offset;
+    int		i;
+    size_t	offset;
 
     FUNC_ENTER(H5T_pack, FAIL);
 
     assert(dt);
     assert(!dt->locked);
 
+    H5T_unshare (dt);
     if (H5T_COMPOUND == dt->type) {
 	/* Recursively pack the members */
 	for (i = 0; i < dt->u.compnd.nmembs; i++) {
@@ -2716,8 +2948,10 @@ H5T_pack(H5T_t *dt)
 	/* Change total size */
 	dt->size = MAX(1, offset);
     }
+    
     FUNC_LEAVE(SUCCEED);
 }
+
 
 /*-------------------------------------------------------------------------
  * Function:	H5T_sort_by_offset
@@ -2740,8 +2974,8 @@ H5T_pack(H5T_t *dt)
 herr_t
 H5T_sort_by_offset(H5T_t *dt)
 {
-    int			    i, j, nmembs;
-    hbool_t		    swapped;
+    int		i, j, nmembs;
+    hbool_t	swapped;
 
     FUNC_ENTER(H5T_sort_by_offset, FAIL);
 
@@ -2771,6 +3005,7 @@ H5T_sort_by_offset(H5T_t *dt)
 
     FUNC_LEAVE(SUCCEED);
 }
+
 
 /*-------------------------------------------------------------------------
  * Function:	H5T_cmp
@@ -2793,10 +3028,10 @@ H5T_sort_by_offset(H5T_t *dt)
 intn
 H5T_cmp(const H5T_t *dt1, const H5T_t *dt2)
 {
-    intn		   *idx1 = NULL, *idx2 = NULL;
-    intn		    ret_value = 0;
-    intn		    i, j, tmp;
-    hbool_t		    swapped;
+    intn	*idx1 = NULL, *idx2 = NULL;
+    intn	ret_value = 0;
+    intn	i, j, tmp;
+    hbool_t	swapped;
 
     FUNC_ENTER(H5T_equal, 0);
 
@@ -3016,6 +3251,7 @@ H5T_cmp(const H5T_t *dt1, const H5T_t *dt2)
     FUNC_LEAVE(ret_value);
 }
 
+
 /*-------------------------------------------------------------------------
  * Function:	H5T_find
  *
@@ -3157,7 +3393,7 @@ H5T_path_find(const H5T_t *src, const H5T_t *dst, hbool_t create,
 	    }
 	    if ((func)(src_id, dst_id, &(path->cdata), 0, NULL, NULL)<0) {
 #ifdef H5T_DEBUG
-		fprintf (stderr, "HDF5-DIAG: conversion function init "
+		fprintf (stderr, "H5T: conversion function init "
 			 "failed\n");
 #endif
 		H5E_clear(); /*ignore the failure*/
@@ -3213,9 +3449,9 @@ H5T_path_find(const H5T_t *src, const H5T_t *dst, hbool_t create,
 herr_t
 H5T_debug(H5T_t *dt, FILE * stream)
 {
-    const char		   *s = "";
-    int			    i, j;
-    uint64		    tmp;
+    const char	*s = "";
+    int		i, j;
+    uint64	tmp;
 
     FUNC_ENTER(H5T_debug, FAIL);
 
diff --git a/src/H5Tconv.c b/src/H5Tconv.c
index 02b7db3..0b4e86f 100644
--- a/src/H5Tconv.c
+++ b/src/H5Tconv.c
@@ -63,7 +63,7 @@ H5T_conv_noop(hid_t src_id, hid_t dst_id, H5T_cdata_t *cdata, size_t nelmts,
 	/* Nothing to free */
 #ifdef H5T_DEBUG
 	if (cdata->ncalls>0) {
-	    fprintf (stderr, "HDF5-DIAG: H5T_conv_noop statistics...\n");
+	    fprintf (stderr, "H5T: H5T_conv_noop statistics...\n");
 	    fprintf (stderr, "   Number of calls:       %lu\n", cdata->ncalls);
 	    fprintf (stderr, "   Data points converted: %lu\n", cdata->nelmts);
 	}
@@ -174,7 +174,7 @@ H5T_conv_order(hid_t src_id, hid_t dst_id, H5T_cdata_t *cdata, size_t nelmts,
 	/* Free private data */
 #ifdef H5T_DEBUG
 	if (cdata->ncalls>0) {
-	    fprintf (stderr, "HDF5-DIAG: H5T_conv_order statistics...\n");
+	    fprintf (stderr, "H5T: H5T_conv_order statistics...\n");
 	    fprintf (stderr, "   Number of calls:       %lu\n", cdata->ncalls);
 	    fprintf (stderr, "   Data points converted: %lu\n", cdata->nelmts);
 	}
@@ -396,7 +396,7 @@ H5T_conv_struct(hid_t src_id, hid_t dst_id, H5T_cdata_t *cdata, size_t nelmts,
 	 */
 #ifdef H5T_DEBUG
 	if (cdata->ncalls>0) {
-	    fprintf (stderr, "HDF5-DIAG: H5T_conv_struct statistics...\n");
+	    fprintf (stderr, "H5T: H5T_conv_struct statistics...\n");
 	    fprintf (stderr, "   Number of calls:       %lu\n", cdata->ncalls);
 	    fprintf (stderr, "   Data points converted: %lu\n", cdata->nelmts);
 	}
diff --git a/src/H5Tpkg.h b/src/H5Tpkg.h
index be52256..84b1235 100644
--- a/src/H5Tpkg.h
+++ b/src/H5Tpkg.h
@@ -23,6 +23,7 @@
 #  undef H5T_DEBUG
 #endif
 
+#include <H5HGprivate.h>
 #include <H5Tprivate.h>
 
 typedef struct H5T_atomic_t {
@@ -62,6 +63,8 @@ typedef struct H5T_compnd_t {
 
 struct H5T_t {
     hbool_t             locked; /*if locked, then can't be modified          */
+    H5HG_t		sh_heap; /*if defined, type is in global heap	     */
+    H5F_t		*sh_file; /*file pointer if this is a shared type    */
     H5T_class_t         type;   /*which class of type is this?               */
     size_t              size;   /*total size of an instance of this type     */
     union {
diff --git a/src/H5Tprivate.h b/src/H5Tprivate.h
index 7ff5d18..27d27f3 100644
--- a/src/H5Tprivate.h
+++ b/src/H5Tprivate.h
@@ -32,6 +32,8 @@ herr_t H5T_init_interface (void);
 H5T_t *H5T_create (H5T_class_t type, size_t size);
 H5T_t *H5T_copy (const H5T_t *old_dt);
 herr_t H5T_close (H5T_t *dt);
+herr_t H5T_share (H5F_t *f, H5T_t *dt);
+herr_t H5T_unshare (H5T_t *dt);
 size_t H5T_get_size (const H5T_t *dt);
 intn H5T_cmp (const H5T_t *dt1, const H5T_t *dt2);
 hbool_t H5T_is_atomic (const H5T_t *dt);
diff --git a/src/H5Tpublic.h b/src/H5Tpublic.h
index f546200..f362cdf 100644
--- a/src/H5Tpublic.h
+++ b/src/H5Tpublic.h
@@ -184,6 +184,7 @@ hid_t H5Tcopy (hid_t type_id);
 herr_t H5Tclose (hid_t type_id);
 hbool_t H5Tequal (hid_t type1_id, hid_t type2_id);
 herr_t H5Tlock (hid_t type_id);
+herr_t H5Tshare (hid_t location_id, hid_t type_id);
 
 /* Operations defined on compound data types */
 herr_t H5Tinsert (hid_t parent_id, const char *name, off_t offset,
diff --git a/src/Makefile.in b/src/Makefile.in
index 7c5a8a5..20b4ae3 100644
--- a/src/Makefile.in
+++ b/src/Makefile.in
@@ -20,7 +20,7 @@ LIB_SRC=H5.c H5AC.c H5B.c H5D.c H5E.c H5F.c H5Farray.c H5Fcore.c H5Ffamily.c  \
 	H5Fistore.c H5Flow.c H5Fsec2.c H5Fsplit.c H5Fstdio.c H5G.c H5Gent.c   \
 	H5Gnode.c H5Gstab.c H5HG.c H5HL.c H5I.c H5MF.c H5MM.c H5O.c H5Ocont.c \
 	H5Odtype.c H5Oefl.c H5Olayout.c H5Oname.c H5Onull.c H5Osdspace.c      \
-	H5Ostab.c H5P.c H5S.c H5Ssimp.c H5T.c H5Tconv.c H5Tinit.c             \
+	H5Oshared.c H5Ostab.c H5P.c H5S.c H5Ssimp.c H5T.c H5Tconv.c H5Tinit.c \
 	H5V.c @PARALLEL_SRC@
 
 LIB_OBJ=$(LIB_SRC:.c=.o)