[svn-r12004] Purpose:

    New feature & code cleanup

Description:
    Update fractal heap to be able to insert objects into a direct block
hanging off the header.

    Extract "octal dump" code into separate routine so that both the local
heaps & fractal heaps can use it.

    Other code cleanups & support to get this far.

Platforms tested:
    FreeBSD 4.11 (sleipnir)
    Linux 2.4

22 files changed, 1796 insertions, 219 deletions

diff --git a/MANIFEST b/MANIFEST
index cdb11d3..3b05f0c 100644
--- a/MANIFEST
+++ b/MANIFEST
@@ -385,6 +385,7 @@
 ./src/hdf5-win.lnt			_DO_NOT_DISTRIBUTE_
 ./src/hdf5-lin.lnt			_DO_NOT_DISTRIBUTE_
 ./src/H5.c
+./src/H5dbg.c
 ./src/H5api_adpt.h
 ./src/H5err.txt
 ./src/H5config.h.in
diff --git a/src/H5AC.c b/src/H5AC.c
index 2d10b03..86e9e17 100644
--- a/src/H5AC.c
+++ b/src/H5AC.c
@@ -743,6 +743,7 @@ static const char * H5AC_entry_type_names[H5AC_NTYPES] =
     "v2 B-tree internal nodes",
     "v2 B-tree leaf nodes",
     "fractal heap headers",
+    "fractal heap direct blocks",
     "test entry"	/* for testing only -- not used for actual files */
 };
 
diff --git a/src/H5ACprivate.h b/src/H5ACprivate.h
index 9817a4a..e50c573 100644
--- a/src/H5ACprivate.h
+++ b/src/H5ACprivate.h
@@ -51,6 +51,7 @@ typedef enum {
     H5AC_BT2_LEAF_ID,	/*v2 B-tree leaf node			     */
     H5AC_TEST_ID,	/*test entry -- not used for actual files    */
     H5AC_FHEAP_HDR_ID,	/*fractal heap header			     */
+    H5AC_FHEAP_DBLOCK_ID, /*fractal heap direct block		     */
     H5AC_NTYPES		/* Number of types, must be last             */
 } H5AC_type_t;
 
diff --git a/src/H5Cpkg.h b/src/H5Cpkg.h
index 7ee4647..155c7f5 100644
--- a/src/H5Cpkg.h
+++ b/src/H5Cpkg.h
@@ -609,7 +609,7 @@
  ****************************************************************************/
 
 #define H5C__H5C_T_MAGIC	0x005CAC0E
-#define H5C__MAX_NUM_TYPE_IDS	10
+#define H5C__MAX_NUM_TYPE_IDS	11
 #define H5C__PREFIX_LEN		32
 
 struct H5C_t
diff --git a/src/H5FDpublic.h b/src/H5FDpublic.h
index 774b3f6..cbfedba 100644
--- a/src/H5FDpublic.h
+++ b/src/H5FDpublic.h
@@ -56,8 +56,8 @@ typedef enum H5FD_mem_t {
  *      -QAK
  */
 #define H5FD_MEM_FHEAP_HDR      H5FD_MEM_OHDR
-#define H5FD_MEM_FHEAP_INDIRECT H5FD_MEM_OHDR
-#define H5FD_MEM_FHEAP_DIRECT   H5FD_MEM_LHEAP
+#define H5FD_MEM_FHEAP_IBLOCK   H5FD_MEM_OHDR
+#define H5FD_MEM_FHEAP_DBLOCK   H5FD_MEM_LHEAP
 
 /*
  * A free-list map which maps all types of allocation requests to a single
diff --git a/src/H5Fprivate.h b/src/H5Fprivate.h
index 8b45ef4..ff6717f 100644
--- a/src/H5Fprivate.h
+++ b/src/H5Fprivate.h
@@ -79,12 +79,10 @@ typedef struct H5F_t H5F_t;
    int64_t _n = (n);							      \
    size_t _i;								      \
    uint8_t *_p = (uint8_t*)(p);						      \
-   for (_i=0; _i<sizeof(int64_t); _i++, _n>>=8) {			      \
+   for (_i = 0; _i < sizeof(int64_t); _i++, _n >>= 8)			      \
       *_p++ = (uint8_t)(_n & 0xff);					      \
-   }									      \
-   for (/*void*/; _i<8; _i++) {						      \
-      *_p++ = (n)<0 ? 0xff : 0;						      \
-   }									      \
+   for (/*void*/; _i < 8; _i++)						      \
+      *_p++ = (n) < 0 ? 0xff : 0;					      \
    (p) = (uint8_t*)(p)+8;						      \
 }
 
@@ -92,13 +90,23 @@ typedef struct H5F_t H5F_t;
    uint64_t _n = (n);							      \
    size_t _i;								      \
    uint8_t *_p = (uint8_t*)(p);						      \
-   for (_i=0; _i<sizeof(uint64_t); _i++, _n>>=8) {			      \
+   for (_i = 0; _i < sizeof(uint64_t); _i++, _n >>= 8)			      \
       *_p++ = (uint8_t)(_n & 0xff);					      \
-   }									      \
-   for (/*void*/; _i<8; _i++) {						      \
+   for (/*void*/; _i < 8; _i++)						      \
       *_p++ = 0;							      \
-   }									      \
-   (p) = (uint8_t*)(p)+8;						      \
+   (p) = (uint8_t*)(p) + 8;						      \
+}
+
+/* Encode a 64-bit unsigned integer into a variable-sized buffer */
+/* (Assumes that the high bits of the integer are zero) */
+#  define UINT64ENCODE_VAR(p, n, l) {					      \
+   uint64_t _n = (n);							      \
+   size_t _i;								      \
+   uint8_t *_p = (uint8_t*)(p);						      \
+									      \
+   for(_i = 0; _i < l; _i++, _n >>= 8)					      \
+      *_p++ = (uint8_t)(_n & 0xff);					      \
+   (p) = (uint8_t*)(p) + l;						      \
 }
 
 /* DECODE converts little endian bytes pointed by p to integer values and store
@@ -140,9 +148,8 @@ typedef struct H5F_t H5F_t;
    size_t _i;								      \
    n = 0;								      \
    (p) += 8;								      \
-   for (_i=0; _i<sizeof(int64_t); _i++) {				      \
-      n = (n<<8) | *(--p);						      \
-   }									      \
+   for (_i = 0; _i < sizeof(int64_t); _i++)					      \
+      n = (n << 8) | *(--p);						      \
    (p) += 8;								      \
 }
 
@@ -151,19 +158,22 @@ typedef struct H5F_t H5F_t;
    size_t _i;								      \
    n = 0;								      \
    (p) += 8;								      \
-   for (_i=0; _i<sizeof(uint64_t); _i++) {				      \
-      n = (n<<8) | *(--p);						      \
-   }									      \
+   for (_i = 0; _i < sizeof(uint64_t); _i++)				      \
+      n = (n << 8) | *(--p);						      \
    (p) += 8;								      \
 }
 
-#define NBYTEENCODE(d, s, n)    do { HDmemcpy(d,s,n); d += n; } while (0)
-
-/*
- * Note:  the NBYTEDECODE macro is backwards from the memcpy() routine, in
- *	  the spirit of the other DECODE macros.
- */
-#define NBYTEDECODE(s, d, n)    do { HDmemcpy(d,s,n); s += n; } while (0)
+/* Decode a variable-sized buffer into a 64-bit unsigned integer */
+/* (Assumes that the high bits of the integer will be zero) */
+#  define UINT64DECODE_VAR(p, n, l) {					      \
+   size_t _i;								      \
+									      \
+   n = 0;								      \
+   (p) += l;								      \
+   for (_i = 0; _i < l; _i++)						      \
+      n = (n << 8) | *(--p);						      \
+   (p) += l;								      \
+}
 
 /* Address-related macros */
 #define H5F_addr_overflow(X,Z)	(HADDR_UNDEF==(X) ||			      \
@@ -237,35 +247,28 @@ typedef struct H5F_t H5F_t;
 
 
 /* Macros to encode/decode offset/length's for storing in the file */
-#ifdef NOT_YET
-#define H5F_ENCODE_OFFSET(f,p,o) (H5F_SIZEOF_ADDR(f)==4 ? UINT32ENCODE(p,o) \
-    : H5F_SIZEOF_ADDR(f)==8 ? UINT64ENCODE(p,o) \
-    : H5F_SIZEOF_ADDR(f)==2 ? UINT16ENCODE(p,o) \
-    : H5FPencode_unusual_offset(f,&(p),(uint8_t*)&(o)))
-#else /* NOT_YET */
 #define H5F_ENCODE_OFFSET(f,p,o) switch(H5F_SIZEOF_ADDR(f)) {		      \
     case 4: UINT32ENCODE(p,o); break;					      \
     case 8: UINT64ENCODE(p,o); break;					      \
     case 2: UINT16ENCODE(p,o); break;					      \
 }
-#endif /* NOT_YET */
 
-#define H5F_DECODE_OFFSET(f,p,o) switch (H5F_SIZEOF_ADDR (f)) {	\
-   case 4: UINT32DECODE (p, o);	break;							\
-   case 8: UINT64DECODE (p, o);	break;							\
-   case 2: UINT16DECODE (p, o);	break;							\
+#define H5F_DECODE_OFFSET(f,p,o) switch (H5F_SIZEOF_ADDR (f)) {		      \
+    case 4: UINT32DECODE(p, o); break;					      \
+    case 8: UINT64DECODE(p, o); break;					      \
+    case 2: UINT16DECODE(p, o); break;					      \
 }
 
-#define H5F_ENCODE_LENGTH(f,p,l) switch(H5F_SIZEOF_SIZE(f)) {   \
-   case 4: UINT32ENCODE(p,l); break;					      \
-   case 8: UINT64ENCODE(p,l); break;					      \
-   case 2: UINT16ENCODE(p,l); break;					      \
+#define H5F_ENCODE_LENGTH(f,p,l) switch(H5F_SIZEOF_SIZE(f)) {		      \
+    case 4: UINT32ENCODE(p,l); break;					      \
+    case 8: UINT64ENCODE(p,l); break;					      \
+    case 2: UINT16ENCODE(p,l); break;					      \
 }
 
-#define H5F_DECODE_LENGTH(f,p,l) switch(H5F_SIZEOF_SIZE(f)) {   \
-   case 4: UINT32DECODE(p,l); break;					      \
-   case 8: UINT64DECODE(p,l); break;					      \
-   case 2: UINT16DECODE(p,l); break;					      \
+#define H5F_DECODE_LENGTH(f,p,l) switch(H5F_SIZEOF_SIZE(f)) {		      \
+    case 4: UINT32DECODE(p,l); break;					      \
+    case 8: UINT64DECODE(p,l); break;					      \
+    case 2: UINT16DECODE(p,l); break;					      \
 }
 
 /*
diff --git a/src/H5HF.c b/src/H5HF.c
index bdc9e00..2577628 100644
--- a/src/H5HF.c
+++ b/src/H5HF.c
@@ -94,7 +94,7 @@ herr_t
 H5HF_create(H5F_t *f, hid_t dxpl_id, H5HF_create_t *cparam, haddr_t *addr_p)
 {
     H5HF_t *fh = NULL;                  /* The new fractal heap header information */
-    herr_t ret_value = SUCCEED;
+    herr_t ret_value = SUCCEED;         /* Return value */
 
     FUNC_ENTER_NOAPI(H5HF_create, FAIL)
 
@@ -102,6 +102,7 @@ H5HF_create(H5F_t *f, hid_t dxpl_id, H5HF_create_t *cparam, haddr_t *addr_p)
      * Check arguments.
      */
     HDassert(f);
+    HDassert(cparam);
     HDassert(addr_p);
 
     /*
@@ -110,18 +111,18 @@ H5HF_create(H5F_t *f, hid_t dxpl_id, H5HF_create_t *cparam, haddr_t *addr_p)
     if(NULL == (fh = H5FL_MALLOC(H5HF_t)))
 	HGOTO_ERROR(H5E_RESOURCE, H5E_NOSPACE, FAIL, "memory allocation failed for fractal heap header")
 
-    /* Assign internal information */
+    /* Reset the metadata cache info for the heap header */
     HDmemset(&fh->cache_info, 0, sizeof(H5AC_info_t));
 
-    /* Initialize shared fractal heap info */
-    if(H5HF_shared_init(fh, cparam) < 0)
-	HGOTO_ERROR(H5E_RESOURCE, H5E_NOSPACE, FAIL, "can't create shared fractal heap info")
-
     /* Allocate space for the header on disk */
     if(HADDR_UNDEF == (*addr_p = H5MF_alloc(f, H5FD_MEM_FHEAP_HDR, dxpl_id, (hsize_t)H5HF_HEADER_SIZE(f))))
 	HGOTO_ERROR(H5E_RESOURCE, H5E_NOSPACE, FAIL, "file allocation failed for fractal heap header")
 
-    /* Cache the new fractal heap node */
+    /* Initialize shared fractal heap info */
+    if(H5HF_shared_create(f, fh, *addr_p, cparam) < 0)
+	HGOTO_ERROR(H5E_RESOURCE, H5E_NOSPACE, FAIL, "can't create shared fractal heap info")
+
+    /* Cache the new fractal heap header */
     if(H5AC_set(f, dxpl_id, H5AC_FHEAP_HDR, *addr_p, fh, H5AC__NO_FLAGS_SET) < 0)
 	HGOTO_ERROR(H5E_HEAP, H5E_CANTINIT, FAIL, "can't add fractal heap header to cache")
 
@@ -159,6 +160,7 @@ H5HF_insert(H5F_t *f, hid_t dxpl_id, haddr_t addr, size_t size,
     herr_t ret_value = SUCCEED;
 
     FUNC_ENTER_NOAPI(H5HF_insert, FAIL)
+HDfprintf(stderr, "%s: size = %Zu\n", FUNC, size);
 
     /*
      * Check arguments.
@@ -181,22 +183,19 @@ H5HF_insert(H5F_t *f, hid_t dxpl_id, haddr_t addr, size_t size,
 
     /* Check if object is large enough to be standalone */
     if(size >= shared->standalone_size) {
-HDfprintf(stderr, "%s: size = %Zu\n", FUNC, size);
 HGOTO_ERROR(H5E_HEAP, H5E_UNSUPPORTED, FAIL, "standalone blocks not supported yet")
     } /* end if */
     else {
         /* Check if we are in "append only" mode, or if there's enough room for the object */
         if(shared->write_once) {
-HDfprintf(stderr, "%s: size = %Zu\n", FUNC, size);
 HGOTO_ERROR(H5E_HEAP, H5E_UNSUPPORTED, FAIL, "'write once' managed blocks not supported yet")
         } /* end if */
         else if(size <= shared->total_man_free) {
-HDfprintf(stderr, "%s: size = %Zu\n", FUNC, size);
 HGOTO_ERROR(H5E_HEAP, H5E_UNSUPPORTED, FAIL, "allocating internal managed blocks not supported yet")
         } /* end if */
         else {
             /* Allocate space at end of heap */
-            if(H5HF_man_alloc_end(shared, size, obj, id) < 0)
+            if(H5HF_man_alloc_end(fh->shared, dxpl_id, &hdr_flags, size, obj, id) < 0)
                 HGOTO_ERROR(H5E_HEAP, H5E_CANTALLOC, FAIL, "can't allocate space at end of managed blocks")
         } /* end else */
     } /* end else */
diff --git a/src/H5HFcache.c b/src/H5HFcache.c
index c20d05d..735037b 100644
--- a/src/H5HFcache.c
+++ b/src/H5HFcache.c
@@ -35,13 +35,19 @@
 #include "H5private.h"		/* Generic Functions			*/
 #include "H5HFpkg.h"		/* Fractal heaps			*/
 #include "H5Eprivate.h"		/* Error handling		  	*/
+#include "H5Vprivate.h"		/* Vectors and arrays 			*/
 
 /****************/
 /* Local Macros */
 /****************/
 
 /* Fractal heap format version #'s */
-#define H5HF_HDR_VERSION 0              /* Header */
+#define H5HF_HDR_VERSION        0               /* Header */
+#define H5HF_DBLOCK_VERSION     0               /* Direct block */
+
+/* Size of free space description in an absolute managed direct block */
+#define H5HF_MAN_ABS_FREE_NODE_SIZE(d) (2 * (d)->blk_off_size)
+
 
 /******************/
 /* Local Typedefs */
@@ -56,12 +62,20 @@ static H5HF_t *H5HF_cache_hdr_load(H5F_t *f, hid_t dxpl_id, haddr_t addr, const
 static herr_t H5HF_cache_hdr_flush(H5F_t *f, hid_t dxpl_id, hbool_t destroy, haddr_t addr, H5HF_t *fh);
 static herr_t H5HF_cache_hdr_clear(H5F_t *f, H5HF_t *fh, hbool_t destroy);
 static herr_t H5HF_cache_hdr_size(const H5F_t *f, const H5HF_t *fh, size_t *size_ptr);
+static H5HF_direct_t *H5HF_cache_dblock_load(H5F_t *f, hid_t dxpl_id, haddr_t addr, const void *_type, void *udata);
+static herr_t H5HF_cache_dblock_flush(H5F_t *f, hid_t dxpl_id, hbool_t destroy, haddr_t addr, H5HF_direct_t *dblock);
+static herr_t H5HF_cache_dblock_clear(H5F_t *f, H5HF_direct_t *dblock, hbool_t destroy);
+static herr_t H5HF_cache_dblock_size(const H5F_t *f, const H5HF_direct_t *dblock, size_t *size_ptr);
+
+/* Local encode/decode routines */
+static herr_t H5HF_dtable_encode(H5F_t *f, uint8_t **pp, const H5HF_dtable_param_t *dt_param);
+static herr_t H5HF_dtable_decode(H5F_t *f, const uint8_t **pp, H5HF_dtable_param_t *dt_param);
 
 /*********************/
 /* Package Variables */
 /*********************/
 
-/* H5HF inherits cache-like properties from H5AC */
+/* H5HF header inherits cache-like properties from H5AC */
 const H5AC_class_t H5AC_FHEAP_HDR[1] = {{
     H5AC_FHEAP_HDR_ID,
     (H5AC_load_func_t)H5HF_cache_hdr_load,
@@ -71,6 +85,16 @@ const H5AC_class_t H5AC_FHEAP_HDR[1] = {{
     (H5AC_size_func_t)H5HF_cache_hdr_size,
 }};
 
+/* H5HF direct block inherits cache-like properties from H5AC */
+const H5AC_class_t H5AC_FHEAP_DBLOCK[1] = {{
+    H5AC_FHEAP_DBLOCK_ID,
+    (H5AC_load_func_t)H5HF_cache_dblock_load,
+    (H5AC_flush_func_t)H5HF_cache_dblock_flush,
+    (H5AC_dest_func_t)H5HF_cache_dblock_dest,
+    (H5AC_clear_func_t)H5HF_cache_dblock_clear,
+    (H5AC_size_func_t)H5HF_cache_dblock_size,
+}};
+
 /*****************************/
 /* Library Private Variables */
 /*****************************/
@@ -80,9 +104,112 @@ const H5AC_class_t H5AC_FHEAP_HDR[1] = {{
 /* Local Variables */
 /*******************/
 
-/* Declare a free list to manage B-tree header data to/from disk */
+/* Declare a free list to manage heap header data to/from disk */
 H5FL_BLK_DEFINE_STATIC(header_block);
 
+/* Declare a free list to manage heap direct block data to/from disk */
+H5FL_BLK_DEFINE(direct_block);
+
+
+
+/*-------------------------------------------------------------------------
+ * Function:	H5HF_dtable_decode
+ *
+ * Purpose:	Decodes the metadata for a doubling table
+ *
+ * Return:	Success:	Pointer to a new fractal heap
+ *
+ *		Failure:	NULL
+ *
+ * Programmer:	Quincey Koziol
+ *		koziol@ncsa.uiuc.edu
+ *		Feb 27 2006
+ *
+ *-------------------------------------------------------------------------
+ */
+static herr_t
+H5HF_dtable_decode(H5F_t *f, const uint8_t **pp, H5HF_dtable_param_t *dt_param)
+{
+    FUNC_ENTER_NOAPI_NOINIT_NOFUNC(H5HF_dtable_decode)
+
+    /* Check arguments */
+    HDassert(f);
+    HDassert(pp && *pp);
+    HDassert(dt_param);
+
+    /* Table width */
+    UINT16DECODE(*pp, dt_param->cparam.width);
+
+    /* Starting block size */
+    H5F_DECODE_LENGTH(f, *pp, dt_param->cparam.start_block_size);
+
+    /* Maximum direct block size */
+    H5F_DECODE_LENGTH(f, *pp, dt_param->cparam.max_direct_size);
+
+    /* Maximum heap size (as # of bits) */
+    UINT16DECODE(*pp, dt_param->cparam.max_index);
+
+    /* Starting # of rows in root indirect block */
+    UINT16DECODE(*pp, dt_param->cparam.start_root_rows);
+
+    /* Address of table */
+    H5F_addr_decode(f, pp, &(dt_param->table_addr));
+
+    /* Current # of rows in root indirect block */
+    UINT16DECODE(*pp, dt_param->curr_root_rows);
+
+    FUNC_LEAVE_NOAPI(SUCCEED)
+} /* end H5HF_dtable_decode() */
+
+
+/*-------------------------------------------------------------------------
+ * Function:	H5HF_dtable_encode
+ *
+ * Purpose:	Encodes the metadata for a doubling table
+ *
+ * Return:	Success:	Pointer to a new fractal heap
+ *
+ *		Failure:	NULL
+ *
+ * Programmer:	Quincey Koziol
+ *		koziol@ncsa.uiuc.edu
+ *		Feb 27 2006
+ *
+ *-------------------------------------------------------------------------
+ */
+static herr_t
+H5HF_dtable_encode(H5F_t *f, uint8_t **pp, const H5HF_dtable_param_t *dt_param)
+{
+    FUNC_ENTER_NOAPI_NOINIT_NOFUNC(H5HF_dtable_encode)
+
+    /* Check arguments */
+    HDassert(f);
+    HDassert(pp && *pp);
+    HDassert(dt_param);
+
+    /* Table width */
+    UINT16ENCODE(*pp, dt_param->cparam.width);
+
+    /* Starting block size */
+    H5F_ENCODE_LENGTH(f, *pp, dt_param->cparam.start_block_size);
+
+    /* Maximum direct block size */
+    H5F_ENCODE_LENGTH(f, *pp, dt_param->cparam.max_direct_size);
+
+    /* Maximum heap size (as # of bits) */
+    UINT16ENCODE(*pp, dt_param->cparam.max_index);
+
+    /* Starting # of rows in root indirect block */
+    UINT16ENCODE(*pp, dt_param->cparam.start_root_rows);
+
+    /* Address of table */
+    H5F_addr_encode(f, pp, dt_param->table_addr);
+
+    /* Current # of rows in root indirect block */
+    UINT16ENCODE(*pp, dt_param->curr_root_rows);
+
+    FUNC_LEAVE_NOAPI(SUCCEED)
+} /* end H5HF_dtable_encode() */
 
 
 /*-------------------------------------------------------------------------
@@ -104,10 +231,10 @@ static H5HF_t *
 H5HF_cache_hdr_load(H5F_t *f, hid_t dxpl_id, haddr_t addr, const void UNUSED *udata1, void UNUSED *udata2)
 {
     H5HF_t		*fh = NULL;     /* Fractal heap info */
+    H5HF_shared_t       *shared = NULL; /* Shared fractal heap information */
     size_t		size;           /* Header size */
     uint8_t		*buf = NULL;    /* Temporary buffer */
-    uint8_t		*p;             /* Pointer into raw data buffer */
-    H5HF_create_t       cparam;         /* Creation parameters for heap */
+    const uint8_t	*p;             /* Pointer into raw data buffer */
     uint32_t            metadata_chksum;        /* Metadata checksum value */
     H5HF_t		*ret_value;     /* Return value */
 
@@ -122,6 +249,11 @@ H5HF_cache_hdr_load(H5F_t *f, hid_t dxpl_id, haddr_t addr, const void UNUSED *ud
 	HGOTO_ERROR(H5E_RESOURCE, H5E_NOSPACE, NULL, "memory allocation failed")
     HDmemset(&fh->cache_info, 0, sizeof(H5AC_info_t));
 
+    /* Allocate & basic initialization for the shared info struct */
+    if(NULL == (shared = H5HF_shared_alloc(f)))
+	HGOTO_ERROR(H5E_RESOURCE, H5E_NOSPACE, NULL, "can't allocate space for shared heap info")
+    shared->heap_addr = addr;
+
     /* Compute the size of the fractal heap header on disk */
     size = H5HF_HEADER_SIZE(f);
 
@@ -135,12 +267,12 @@ H5HF_cache_hdr_load(H5F_t *f, hid_t dxpl_id, haddr_t addr, const void UNUSED *ud
 
     p = buf;
 
-    /* magic number */
+    /* Magic number */
     if(HDmemcmp(p, H5HF_HDR_MAGIC, H5HF_SIZEOF_MAGIC))
 	HGOTO_ERROR(H5E_HEAP, H5E_CANTLOAD, NULL, "wrong fractal heap header signature")
     p += H5HF_SIZEOF_MAGIC;
 
-    /* version */
+    /* Version */
     if(*p++ != H5HF_HDR_VERSION)
 	HGOTO_ERROR(H5E_HEAP, H5E_CANTLOAD, NULL, "wrong fractal heap header version")
 
@@ -156,21 +288,29 @@ H5HF_cache_hdr_load(H5F_t *f, hid_t dxpl_id, haddr_t addr, const void UNUSED *ud
 	HGOTO_ERROR(H5E_HEAP, H5E_CANTLOAD, NULL, "incorrect metadata checksum for fractal heap header")
 
     /* Heap address mapping */
-    cparam.addrmap = *p++;
+    shared->addrmap = *p++;
     HDassert(H5HF_ABSOLUTE == 0);
-    if(cparam.addrmap > H5HF_MAPPED)
-	HGOTO_ERROR(H5E_HEAP, H5E_CANTLOAD, NULL, "incorrect fractal heap type")
+    if(shared->addrmap > H5HF_MAPPED)
+	HGOTO_ERROR(H5E_HEAP, H5E_CANTLOAD, NULL, "incorrect fractal heap address mapping")
 
     /* Min. size of standalone objects */
-    UINT32DECODE(p, cparam.standalone_size);
+    UINT32DECODE(p, shared->standalone_size);
+
+    /* Length of fixed-length objects in heap */
+    UINT32DECODE(p, shared->fixed_len_size);
 
-    /* Size of fixed-length objects in heap */
-    UINT32DECODE(p, cparam.fixed_len_size);
+    /* Size of ref. count for objects in heap */
+    shared->ref_count_size = *p++;
+
+    /* Managed objects' doubling-table info */
+    if(H5HF_dtable_decode(shared->f, &p, &(shared->man_dtable_info)) < 0)
+        HGOTO_ERROR(H5E_HEAP, H5E_CANTENCODE, NULL, "unable to encode managed obj. doubling table info")
 
-    /* Initialize shared fractal heap info */
     HDassert((size_t)(p - buf) == size);
-    if(H5HF_shared_init(fh, &cparam) < 0)
-	HGOTO_ERROR(H5E_RESOURCE, H5E_NOSPACE, NULL, "can't create shared fractal heap info")
+
+    /* Make shared heap info reference counted */
+    if(H5HF_shared_own(fh, shared) < 0)
+	HGOTO_ERROR(H5E_RESOURCE, H5E_NOSPACE, NULL, "can't create ref-count wrapper for shared fractal heap info")
 
     /* Set return value */
     ret_value = fh;
@@ -201,6 +341,7 @@ done:
 static herr_t
 H5HF_cache_hdr_flush(H5F_t *f, hid_t dxpl_id, hbool_t destroy, haddr_t addr, H5HF_t *fh)
 {
+    H5HF_shared_t *shared;              /* Shared fractal heap information */
     herr_t      ret_value = SUCCEED;    /* Return value */
 
     FUNC_ENTER_NOAPI(H5HF_cache_hdr_flush, FAIL)
@@ -210,17 +351,16 @@ H5HF_cache_hdr_flush(H5F_t *f, hid_t dxpl_id, hbool_t destroy, haddr_t addr, H5H
     HDassert(H5F_addr_defined(addr));
     HDassert(fh);
 
+    /* Get the pointer to the shared heap info */
+    shared = H5RC_GET_OBJ(fh->shared);
+    HDassert(shared);
+
     if(fh->cache_info.is_dirty) {
-        H5HF_shared_t *shared;      /* Shared fractal heap information */
         uint8_t	*buf = NULL;        /* Temporary raw data buffer */
         uint8_t *p;                 /* Pointer into raw data buffer */
         size_t	size;               /* Header size on disk */
 
-        /* Get the pointer to the shared B-tree info */
-        shared = H5RC_GET_OBJ(fh->shared);
-        HDassert(shared);
-
-        /* Compute the size of the B-tree header on disk */
+        /* Compute the size of the heap header on disk */
         size = H5HF_HEADER_SIZE(f);
 
         /* Allocate temporary buffer */
@@ -254,7 +394,14 @@ H5HF_cache_hdr_flush(H5F_t *f, hid_t dxpl_id, hbool_t destroy, haddr_t addr, H5H
         /* Size of fixed-length objects in heap */
         UINT32ENCODE(p, shared->fixed_len_size);
 
-	/* Write the B-tree header. */
+        /* Size of ref. count for objects in heap */
+        *p++ = shared->ref_count_size;
+
+        /* Managed objects' doubling-table info */
+        if(H5HF_dtable_encode(shared->f, &p, &(shared->man_dtable_info)) < 0)
+	    HGOTO_ERROR(H5E_HEAP, H5E_CANTENCODE, FAIL, "unable to encode managed obj. doubling table info")
+
+	/* Write the heap header. */
         HDassert((size_t)(p - buf) == size);
 	if(H5F_block_write(f, H5FD_MEM_FHEAP_HDR, addr, size, dxpl_id, buf) < 0)
 	    HGOTO_ERROR(H5E_HEAP, H5E_CANTFLUSH, FAIL, "unable to save fractal heap header to disk")
@@ -375,3 +522,367 @@ H5HF_cache_hdr_size(const H5F_t *f, const H5HF_t UNUSED *fh, size_t *size_ptr)
     FUNC_LEAVE_NOAPI(SUCCEED)
 } /* H5HF_cache_hdr_size() */
 
+
+/*-------------------------------------------------------------------------
+ * Function:	H5HF_cache_dblock_load
+ *
+ * Purpose:	Loads a fractal heap direct block from the disk.
+ *
+ * Return:	Success:	Pointer to a new fractal heap direct block
+ *
+ *		Failure:	NULL
+ *
+ * Programmer:	Quincey Koziol
+ *		koziol@ncsa.uiuc.edu
+ *		Feb 27 2006
+ *
+ *-------------------------------------------------------------------------
+ */
+static H5HF_direct_t *
+H5HF_cache_dblock_load(H5F_t *f, hid_t dxpl_id, haddr_t addr, const void *_size, void *_fh_shared)
+{
+    const size_t        *size = (const size_t *)_size;         /* Size of block */
+    H5RC_t 		*fh_shared = (H5RC_t *)_fh_shared;     /* Shared heap information */
+    H5HF_shared_t       *shared = NULL; /* Shared fractal heap information */
+    H5HF_direct_t	*dblock = NULL; /* Direct block info */
+    uint8_t		*buf = NULL;    /* Temporary buffer */
+    const uint8_t	*p;             /* Pointer into raw data buffer */
+    haddr_t             heap_addr;      /* Address of heap header in the file */
+    uint32_t            metadata_chksum;        /* Metadata checksum value */
+    H5HF_direct_t	*ret_value;     /* Return value */
+
+    FUNC_ENTER_NOAPI(H5HF_cache_dblock_load, NULL)
+
+    /* Check arguments */
+    HDassert(f);
+    HDassert(H5F_addr_defined(addr));
+    HDassert(fh_shared);
+
+    /* Allocate space for the fractal heap direct block */
+    if(NULL == (dblock = H5FL_MALLOC(H5HF_direct_t)))
+	HGOTO_ERROR(H5E_RESOURCE, H5E_NOSPACE, NULL, "memory allocation failed")
+    HDmemset(&dblock->cache_info, 0, sizeof(H5AC_info_t));
+
+    /* Share common heap information */
+    dblock->shared = fh_shared;
+    H5RC_INC(dblock->shared);
+
+    /* Get the pointer to the shared heap info */
+    shared = H5RC_GET_OBJ(dblock->shared);
+    HDassert(shared);
+
+    /* Set block's internal information */
+    dblock->size = *size;
+    dblock->blk_off_size = H5HF_SIZEOF_OFFSET_LEN(dblock->size);
+    dblock->free_list = NULL;
+
+    /* Allocate block buffer */
+/* XXX: Change to using free-list factories */
+    if((buf = H5FL_BLK_MALLOC(direct_block, (size_t)dblock->size)) == NULL)
+        HGOTO_ERROR(H5E_RESOURCE, H5E_NOSPACE, NULL, "memory allocation failed")
+
+    /* Read header from disk */
+    if(H5F_block_read(f, H5FD_MEM_FHEAP_HDR, addr, (size_t)dblock->size, dxpl_id, buf) < 0)
+	HGOTO_ERROR(H5E_HEAP, H5E_READERROR, NULL, "can't read fractal heap direct block")
+
+    p = buf;
+
+    /* Magic number */
+    if(HDmemcmp(p, H5HF_DBLOCK_MAGIC, H5HF_SIZEOF_MAGIC))
+	HGOTO_ERROR(H5E_HEAP, H5E_CANTLOAD, NULL, "wrong fractal heap direct block signature")
+    p += H5HF_SIZEOF_MAGIC;
+
+    /* Version */
+    if(*p++ != H5HF_DBLOCK_VERSION)
+	HGOTO_ERROR(H5E_HEAP, H5E_CANTLOAD, NULL, "wrong fractal heap direct block version")
+
+    /* Metadata flags (unused, currently) */
+/* XXX: Plan out metadata flags (including "read-only duplicate" feature) */
+    if(*p++ != 0)
+	HGOTO_ERROR(H5E_HEAP, H5E_CANTLOAD, NULL, "unknown metadata flag in fractal heap direct block")
+
+    /* Metadata checksum (unused, currently) */
+    UINT32DECODE(p, metadata_chksum);
+/* XXX: Verify checksum */
+    if(metadata_chksum != 0)
+	HGOTO_ERROR(H5E_HEAP, H5E_CANTLOAD, NULL, "incorrect metadata checksum for fractal heap direct block")
+
+    /* Address of heap that owns this block (skip) */
+    H5F_addr_decode(f, &p, &heap_addr);
+    if(H5F_addr_ne(heap_addr, shared->heap_addr))
+	HGOTO_ERROR(H5E_HEAP, H5E_CANTLOAD, NULL, "incorrect heap header address for direct block")
+    
+    /* Offset of heap within the heap's address space */
+    UINT64DECODE_VAR(p, dblock->block_off, shared->heap_off_size);
+
+    /* Total free space in block */
+    UINT64DECODE_VAR(p, dblock->blk_free_space, dblock->blk_off_size);
+
+    /* Offset of free list head */
+    /* (Defer deserializing the whole free list until we actually need to modify it) */
+    UINT64DECODE_VAR(p, dblock->free_list_head, dblock->blk_off_size);
+
+    /* Keep pointer to block buffer */
+    dblock->blk = buf;
+
+    /* Set return value */
+    ret_value = dblock;
+
+done:
+    if(!ret_value && dblock)
+        (void)H5HF_cache_dblock_dest(f, dblock);
+
+    FUNC_LEAVE_NOAPI(ret_value)
+} /* end H5HF_cache_dblock_load() */
+
+
+/*-------------------------------------------------------------------------
+ * Function:	H5HF_cache_dblock_flush
+ *
+ * Purpose:	Flushes a dirty fractal heap direct block to disk.
+ *
+ * Return:	Non-negative on success/Negative on failure
+ *
+ * Programmer:	Quincey Koziol
+ *		koziol@ncsa.uiuc.edu
+ *		Feb 27 2006
+ *
+ *-------------------------------------------------------------------------
+ */
+static herr_t
+H5HF_cache_dblock_flush(H5F_t *f, hid_t dxpl_id, hbool_t destroy, haddr_t addr, H5HF_direct_t *dblock)
+{
+    herr_t      ret_value = SUCCEED;    /* Return value */
+
+    FUNC_ENTER_NOAPI(H5HF_cache_dblock_flush, FAIL)
+
+    /* check arguments */
+    HDassert(f);
+    HDassert(H5F_addr_defined(addr));
+    HDassert(dblock);
+
+    if(dblock->cache_info.is_dirty) {
+        H5HF_shared_t *shared;      /* Shared fractal heap information */
+        uint8_t *p;                 /* Pointer into raw data buffer */
+
+        /* Get the pointer to the shared heap info */
+        shared = H5RC_GET_OBJ(dblock->shared);
+        HDassert(shared);
+
+        p = dblock->blk;
+
+        /* Magic number */
+        HDmemcpy(p, H5HF_DBLOCK_MAGIC, H5HF_SIZEOF_MAGIC);
+        p += H5HF_SIZEOF_MAGIC;
+
+        /* Version # */
+        *p++ = H5HF_DBLOCK_VERSION;
+
+        /* Metadata status flags */
+/* XXX: Set this? */
+        *p++ = 0;
+
+        /* Metadata checksum */
+/* XXX: Set this!  (After all the metadata is in the buffer) */
+        HDmemset(p, 0, 4);
+        p += 4;
+
+        /* Address of heap header for heap which owns this block */
+        H5F_addr_encode(f, &p, shared->heap_addr);
+
+        /* Offset of block in heap */
+        UINT64ENCODE_VAR(p, dblock->block_off, shared->heap_off_size);
+
+        /* Check for (currently) unsupported address mapping */
+        if(shared->addrmap != H5HF_ABSOLUTE)
+            HGOTO_ERROR(H5E_HEAP, H5E_UNSUPPORTED, FAIL, "encoding mapped direct blocks not supported currently")
+
+        /* Total free space in block */
+        UINT64ENCODE_VAR(p, dblock->blk_free_space, dblock->blk_off_size);
+
+        /* Offset of free list head */
+        UINT64ENCODE_VAR(p, dblock->free_list_head, dblock->blk_off_size);
+
+        /* Sanity check */
+        HDassert((size_t)(p - dblock->blk) == H5HF_MAN_ABS_DIRECT_OVERHEAD_DBLOCK(shared, dblock));
+
+        /* Check for dirty free list */
+        if(dblock->free_list && dblock->free_list->dirty) {
+            H5HF_direct_free_node_t *node;      /* Pointer to free list node for block */
+
+            /* Loop over all free list blocks, updating their data */
+            node = dblock->free_list->first;
+            while(node) {
+                /* Find first node which has enough room to describe free space */
+                while(node && node->size < H5HF_MAN_ABS_FREE_NODE_SIZE(dblock))
+                    node = node->next;
+
+                /* Check for free space node to encode */
+                if(node) {
+                    H5HF_direct_free_node_t *next_node; /* Pointer to next free list node for block */
+
+                    /* Probe ahead for next node that is large enough to encode free space description */
+                    next_node = node->next;
+                    while(next_node && next_node->size < H5HF_MAN_ABS_FREE_NODE_SIZE(dblock))
+                        next_node = next_node->next;
+
+                    /* Encode information for this node on free list */
+                    p = dblock->blk + node->my_offset;
+                    UINT64ENCODE_VAR(p, node->size, dblock->blk_off_size);
+                    UINT64ENCODE_VAR(p, (next_node ? next_node->my_offset : 0), dblock->blk_off_size);
+
+                    /* Advance to next node */
+                    node = node->next;
+                } /* end if */
+
+            } /* end while */
+
+            /* Reset the free list dirty flag */
+            dblock->free_list->dirty = FALSE;
+        } /* end if */
+
+	/* Write the heap header. */
+	if(H5F_block_write(f, H5FD_MEM_FHEAP_HDR, addr, (size_t)dblock->size, dxpl_id, dblock->blk) < 0)
+	    HGOTO_ERROR(H5E_HEAP, H5E_CANTFLUSH, FAIL, "unable to save fractal heap direct block to disk")
+
+	dblock->cache_info.is_dirty = FALSE;
+    } /* end if */
+
+    if(destroy)
+        if(H5HF_cache_dblock_dest(f, dblock) < 0)
+	    HGOTO_ERROR(H5E_HEAP, H5E_CANTFREE, FAIL, "unable to destroy fractal heap direct block")
+
+done:
+    FUNC_LEAVE_NOAPI(ret_value)
+} /* H5HF_cache_dblock_flush() */
+
+
+/*-------------------------------------------------------------------------
+ * Function:	H5HF_cache_dblock_dest
+ *
+ * Purpose:	Destroys a fractal heap direct block in memory.
+ *
+ * Return:	Non-negative on success/Negative on failure
+ *
+ * Programmer:	Quincey Koziol
+ *		koziol@ncsa.uiuc.edu
+ *		Feb 27 2006
+ *
+ *-------------------------------------------------------------------------
+ */
+/* ARGSUSED */
+herr_t
+H5HF_cache_dblock_dest(H5F_t UNUSED *f, H5HF_direct_t *dblock)
+{
+    FUNC_ENTER_NOAPI_NOINIT_NOFUNC(H5HF_cache_dblock_dest)
+
+    /*
+     * Check arguments.
+     */
+    HDassert(dblock);
+
+    /* Decrement reference count on shared fractal heap info */
+    if(dblock->shared)
+        H5RC_DEC(dblock->shared);
+
+    /* Check for free list & free it, if necessary */
+    if(dblock->free_list) {
+        H5HF_direct_free_node_t *node; /* Pointer to free list node for block */
+
+        /* Walk through list, freeing the nodes */
+        node = dblock->free_list->first;
+        while(node) {
+            H5HF_direct_free_node_t *last_node; /* Pointer to last free list node for block */
+
+            /* Advance to next node */
+            last_node = node;
+            node = node->next;
+
+            /* Release the last node */
+            H5FL_FREE(H5HF_direct_free_node_t, last_node);
+        } /* end while */
+
+        /* Release the free list head */
+        H5FL_FREE(H5HF_direct_free_head_t, dblock->free_list);
+    } /* end if */
+
+    /* Free block's buffer */
+    H5FL_BLK_FREE(direct_block, dblock->blk);
+
+    /* Free fractal heap direct block info */
+    H5FL_FREE(H5HF_direct_t, dblock);
+
+    FUNC_LEAVE_NOAPI(SUCCEED)
+} /* end H5HF_cache_dblock_dest() */
+
+
+/*-------------------------------------------------------------------------
+ * Function:	H5HF_cache_dblock_clear
+ *
+ * Purpose:	Mark a fractal heap direct block in memory as non-dirty.
+ *
+ * Return:	Non-negative on success/Negative on failure
+ *
+ * Programmer:	Quincey Koziol
+ *		koziol@ncsa.uiuc.edu
+ *		Feb 27 2006
+ *
+ *-------------------------------------------------------------------------
+ */
+static herr_t
+H5HF_cache_dblock_clear(H5F_t *f, H5HF_direct_t *dblock, hbool_t destroy)
+{
+    herr_t ret_value = SUCCEED;         /* Return value */
+
+    FUNC_ENTER_NOAPI_NOINIT(H5HF_cache_dblock_clear)
+
+    /*
+     * Check arguments.
+     */
+    HDassert(dblock);
+
+    /* Reset the free list dirty flag */
+    dblock->free_list->dirty = FALSE;
+
+    /* Reset the dirty flag.  */
+    dblock->cache_info.is_dirty = FALSE;
+
+    if(destroy)
+        if(H5HF_cache_dblock_dest(f, dblock) < 0)
+	    HGOTO_ERROR(H5E_HEAP, H5E_CANTFREE, FAIL, "unable to destroy fractal heap direct block")
+
+done:
+    FUNC_LEAVE_NOAPI(ret_value)
+} /* end H5HF_cache_dblock_clear() */
+
+
+/*-------------------------------------------------------------------------
+ * Function:	H5HF_cache_block_size
+ *
+ * Purpose:	Compute the size in bytes of a fractal heap direct block
+ *		on disk, and return it in *size_ptr.  On failure,
+ *		the value of *size_ptr is undefined.
+ *
+ * Return:	Non-negative on success/Negative on failure
+ *
+ * Programmer:	Quincey Koziol
+ *		koziol@ncsa.uiuc.edu
+ *		Feb 24 2006
+ *
+ *-------------------------------------------------------------------------
+ */
+static herr_t
+H5HF_cache_dblock_size(const H5F_t UNUSED *f, const H5HF_direct_t *dblock, size_t *size_ptr)
+{
+    FUNC_ENTER_NOAPI_NOINIT_NOFUNC(H5HF_cache_dblock_size)
+
+    /* check arguments */
+    HDassert(dblock);
+    HDassert(size_ptr);
+
+    /* Set size value */
+    *size_ptr = dblock->size;
+
+    FUNC_LEAVE_NOAPI(SUCCEED)
+} /* H5HF_cache_dblock_size() */
+
diff --git a/src/H5HFdbg.c b/src/H5HFdbg.c
index 4216e96..2024402 100644
--- a/src/H5HFdbg.c
+++ b/src/H5HFdbg.c
@@ -33,9 +33,10 @@
 /* Headers */
 /***********/
 #include "H5private.h"		/* Generic Functions			*/
-#include "H5HFpkg.h"		/* Fractal heaps			*/
 #include "H5Eprivate.h"		/* Error handling		  	*/
 #include "H5FLprivate.h"	/* Free Lists                           */
+#include "H5HFpkg.h"		/* Fractal heaps			*/
+#include "H5MMprivate.h"	/* Memory management			*/
 
 /****************/
 /* Local Macros */
@@ -51,6 +52,9 @@
 /* Local Prototypes */
 /********************/
 
+static herr_t H5HF_dtable_debug(H5HF_dtable_param_t *dt_param, FILE *stream,
+    int indent, int fwidth);
+
 
 /*********************/
 /* Package Variables */
@@ -68,6 +72,61 @@
 
 
 /*-------------------------------------------------------------------------
+ * Function:	H5HF_dtable_debug
+ *
+ * Purpose:	Prints debugging info about a doubling table
+ *
+ * Return:	Non-negative on success/Negative on failure
+ *
+ * Programmer:	Quincey Koziol
+ *		koziol@ncsa.uiuc.edu
+ *		Feb 28 2006
+ *
+ *-------------------------------------------------------------------------
+ */
+static herr_t
+H5HF_dtable_debug(H5HF_dtable_param_t *dt_param, FILE *stream, int indent, int fwidth)
+{
+    FUNC_ENTER_NOAPI_NOINIT_NOFUNC(H5HF_dtable_debug)
+
+    /*
+     * Check arguments.
+     */
+    HDassert(dt_param);
+    HDassert(stream);
+    HDassert(indent >= 0);
+    HDassert(fwidth >= 0);
+
+    /*
+     * Print the values.
+     */
+    HDfprintf(stream, "%*s%-*s %u\n", indent, "", fwidth,
+	      "Doubling table width:",
+	      dt_param->cparam.width);
+    HDfprintf(stream, "%*s%-*s %Zu\n", indent, "", fwidth,
+	      "Starting block size:",
+	      dt_param->cparam.start_block_size);
+    HDfprintf(stream, "%*s%-*s %Zu\n", indent, "", fwidth,
+	      "Max. direct block size:",
+	      dt_param->cparam.max_direct_size);
+    HDfprintf(stream, "%*s%-*s %u (bits)\n", indent, "", fwidth,
+	      "Max. index size:",
+	      dt_param->cparam.max_index);
+    HDfprintf(stream, "%*s%-*s %u\n", indent, "", fwidth,
+	      "Starting # of rows in root indirect block:",
+	      dt_param->cparam.start_root_rows);
+    HDfprintf(stream, "%*s%-*s %a\n", indent, "", fwidth,
+	      "Table's root address:",
+	      dt_param->table_addr);
+    HDfprintf(stream, "%*s%-*s %u\n", indent, "", fwidth,
+	      "Current # of rows in root indirect block:",
+	      dt_param->curr_root_rows);
+
+    FUNC_LEAVE_NOAPI(SUCCEED)
+} /* end H5HF_dtable_debug() */
+
+
+/*-------------------------------------------------------------------------
  * Function:	H5HF_hdr_debug
  *
  * Purpose:	Prints debugging info about a fractal heap header.
@@ -102,7 +161,7 @@ H5HF_hdr_debug(H5F_t *f, hid_t dxpl_id, haddr_t addr, FILE *stream, int indent,
      * Load the fractal heap header.
      */
     if(NULL == (fh = H5AC_protect(f, dxpl_id, H5AC_FHEAP_HDR, addr, NULL, NULL, H5AC_READ)))
-	HGOTO_ERROR(H5E_BTREE, H5E_CANTLOAD, FAIL, "unable to load fractal heap header")
+	HGOTO_ERROR(H5E_HEAP, H5E_CANTLOAD, FAIL, "unable to load fractal heap header")
 
     /* Get the pointer to the shared fractal heap info */
     shared = H5RC_GET_OBJ(fh->shared);
@@ -125,11 +184,167 @@ H5HF_hdr_debug(H5F_t *f, hid_t dxpl_id, haddr_t addr, FILE *stream, int indent,
     HDfprintf(stream, "%*s%-*s %lu\n", indent, "", fwidth,
 	      "Fixed length object size:",
 	      (unsigned long)shared->fixed_len_size);
+    HDfprintf(stream, "%*s%-*s %u\n", indent, "", fwidth,
+	      "Ref. count size:",
+	      (unsigned)shared->ref_count_size);
+
+    HDfprintf(stream, "%*sManaged Objects Doubling-Table Info...\n", indent, "");
+    H5HF_dtable_debug(&shared->man_dtable_info, stream, indent + 3, MAX(0, fwidth -3));
 
 done:
     if(fh && H5AC_unprotect(f, dxpl_id, H5AC_FHEAP_HDR, addr, fh, H5AC__NO_FLAGS_SET) < 0)
-        HDONE_ERROR(H5E_BTREE, H5E_PROTECT, FAIL, "unable to release fractal heap header")
+        HDONE_ERROR(H5E_HEAP, H5E_PROTECT, FAIL, "unable to release fractal heap header")
 
     FUNC_LEAVE_NOAPI(ret_value)
 } /* end H5HF_hdr_debug() */
 
+
+/*-------------------------------------------------------------------------
+ * Function:	H5HF_dblock_debug
+ *
+ * Purpose:	Prints debugging info about a fractal heap direct block.
+ *
+ * Return:	Non-negative on success/Negative on failure
+ *
+ * Programmer:	Quincey Koziol
+ *		koziol@ncsa.uiuc.edu
+ *		Feb 28 2006
+ *
+ *-------------------------------------------------------------------------
+ */
+herr_t
+H5HF_dblock_debug(H5F_t *f, hid_t dxpl_id, haddr_t addr, FILE *stream,
+    int indent, int fwidth, haddr_t hdr_addr, size_t block_size)
+{
+    H5HF_t	*fh = NULL;             /* Fractal heap header info */
+    H5HF_direct_t *dblock = NULL;       /* Fractal heap direct block info */
+    H5HF_direct_free_node_t *node;      /* Pointer to free list node for block */
+    H5HF_shared_t *shared;              /* Shared fractal heap information */
+    size_t	blk_prefix_size;        /* Size of prefix for block */
+    unsigned    node_count = 0;         /* Number of free space nodes */
+    size_t	amount_free = 0;        /* Amount of free space in block */
+    uint8_t	*marker = NULL;         /* Track free space for block */
+    size_t	overlap;                /* Number of free space overlaps */
+    size_t	u, v;                   /* Local index variable */
+    herr_t      ret_value = SUCCEED;    /* Return value */
+
+    FUNC_ENTER_NOAPI(H5HF_dblock_debug, FAIL)
+
+    /*
+     * Check arguments.
+     */
+    HDassert(f);
+    HDassert(H5F_addr_defined(addr));
+    HDassert(stream);
+    HDassert(indent >= 0);
+    HDassert(fwidth >= 0);
+    HDassert(H5F_addr_defined(hdr_addr));
+    HDassert(block_size > 0);
+
+    /*
+     * Load the fractal heap header.
+     */
+    if(NULL == (fh = H5AC_protect(f, dxpl_id, H5AC_FHEAP_HDR, hdr_addr, NULL, NULL, H5AC_READ)))
+	HGOTO_ERROR(H5E_HEAP, H5E_CANTLOAD, FAIL, "unable to load fractal heap header")
+
+    /* Get the pointer to the shared fractal heap info */
+    shared = H5RC_GET_OBJ(fh->shared);
+    HDassert(shared);
+
+    /*
+     * Load the heap direct block
+     */
+    if(NULL == (dblock = H5AC_protect(f, dxpl_id, H5AC_FHEAP_DBLOCK, addr, &block_size, fh->shared, H5AC_READ)))
+	HGOTO_ERROR(H5E_HEAP, H5E_CANTLOAD, FAIL, "unable to load fractal heap direct block")
+
+    /* Release the heap header */
+    if(H5AC_unprotect(f, dxpl_id, H5AC_FHEAP_HDR, hdr_addr, fh, H5AC__NO_FLAGS_SET) < 0)
+        HDONE_ERROR(H5E_HEAP, H5E_PROTECT, FAIL, "unable to release fractal heap header")
+    fh = NULL;
+
+    /* Print opening message */
+    HDfprintf(stream, "%*sFractal Heap Direct Block...\n", indent, "");
+
+    /*
+     * Print the values.
+     */
+    HDfprintf(stream, "%*s%-*s %a\n", indent, "", fwidth,
+	      "Address of fractal heap that owns this block:",
+	      shared->heap_addr);
+    HDfprintf(stream, "%*s%-*s %Hu\n", indent, "", fwidth,
+	      "Offset of direct block in heap:",
+	      dblock->block_off);
+    blk_prefix_size = H5HF_MAN_ABS_DIRECT_OVERHEAD_DBLOCK(shared, dblock);
+    HDfprintf(stream, "%*s%-*s %Zu\n", indent, "", fwidth,
+	      "Size of prefix:",
+              blk_prefix_size);
+    HDfprintf(stream, "%*s%-*s %Zu\n", indent, "", fwidth,
+	      "Size of block offsets:",
+	      dblock->blk_off_size);
+    HDfprintf(stream, "%*s%-*s %Zu\n", indent, "", fwidth,
+	      "Total free space in block:",
+	      dblock->blk_free_space);
+    HDfprintf(stream, "%*s%-*s %Zu\n", indent, "", fwidth,
+	      "Offset of free list head:",
+	      dblock->free_list_head);
+
+    /* Check for valid free list */
+    if(!dblock->free_list)
+        if(H5HF_man_dblock_build_freelist(dblock) < 0)
+            HGOTO_ERROR(H5E_HEAP, H5E_CANTDECODE, FAIL, "can't decode free list for block")
+    HDassert(dblock->free_list);
+
+    /*
+     * Traverse the free list and check that all free blocks fall within
+     * the block and that no two free blocks point to the same region of
+     * the block.  */
+    if(NULL == (marker = H5MM_calloc(dblock->size)))
+	HGOTO_ERROR(H5E_RESOURCE, H5E_NOSPACE, FAIL, "memory allocation failed")
+
+    HDfprintf(stream, "%*sFree Blocks (offset, next offset, size):\n", indent, "");
+    node = dblock->free_list->first;
+    while(node) {
+        char temp_str[32];
+
+        sprintf(temp_str, "Block #%u:", node_count);
+	HDfprintf(stream, "%*s%-*s %8Zu, %8Zu, %8Zu\n", indent + 3, "", MAX(0, fwidth - 9),
+		temp_str,
+		node->my_offset, node->next_offset, node->size);
+
+	if (node->my_offset + node->size > dblock->size)
+	    fprintf(stream, "***THAT FREE BLOCK IS OUT OF BOUNDS!\n");
+        else {
+            /* Mark this node's free space & check for overlaps w/other free space */
+	    for(u = overlap = 0; u < node->size; u++) {
+		if(marker[node->my_offset + u])
+		    overlap++;
+		marker[node->my_offset + u] = 1;
+	    } /* end for */
+
+	    if (overlap)
+		fprintf(stream, "***THAT FREE BLOCK OVERLAPPED A PREVIOUS ONE!\n");
+	    else
+		amount_free += node->size;
+	} /* end else */
+
+        /* Avance to next node */
+        node = node->next;
+        node_count++;
+    } /* end while */
+
+    HDfprintf(stream, "%*s%-*s %.2f%%\n", indent, "", fwidth,
+            "Percent of block used:",
+            (100.0 * (double)(dblock->size - (blk_prefix_size + amount_free)) / (double)dblock->size));
+
+    /*
+     * Print the data in a VMS-style octal dump.
+     */
+    H5_buffer_dump(stream, indent, dblock->blk, marker, 0, dblock->size);
+
+done:
+    if(dblock && H5AC_unprotect(f, dxpl_id, H5AC_FHEAP_DBLOCK, addr, dblock, H5AC__NO_FLAGS_SET) < 0)
+        HDONE_ERROR(H5E_HEAP, H5E_PROTECT, FAIL, "unable to release fractal heap direct block")
+
+    FUNC_LEAVE_NOAPI(ret_value)
+} /* end H5HF_dblock_debug() */
+
diff --git a/src/H5HFint.c b/src/H5HFint.c
index 83bb780..cff06f4 100644
--- a/src/H5HFint.c
+++ b/src/H5HFint.c
@@ -36,11 +36,17 @@
 #include "H5HFpkg.h"		/* Fractal heaps			*/
 #include "H5Eprivate.h"		/* Error handling		  	*/
 #include "H5MFprivate.h"	/* File memory management		*/
+#include "H5Vprivate.h"		/* Vectors and arrays 			*/
 
 /****************/
 /* Local Macros */
 /****************/
 
+/* Limit on the size of the max. direct block size */
+/* (This is limited to 32-bits currently, because I think it's unlikely to
+ *      need to be larger, and the 32-bit limit for H5V_log2(n)  - QAK)
+ */
+#define H5HL_MAX_DIRECT_SIZE_LIMIT ((hsize_t)2 * 1024 * 1024 * 1024)
 
 /******************/
 /* Local Typedefs */
@@ -52,11 +58,25 @@
 /********************/
 
 static herr_t H5HF_shared_free(void *_shared);
+static herr_t H5HF_man_dblock_create(H5RC_t *fh_shared, hid_t dxpl_id,
+    size_t block_size, hsize_t block_off, haddr_t *addr_p);
+static herr_t H5HF_man_dblock_insert(H5RC_t *fh_shared, hid_t dxpl_id,
+    haddr_t block_addr, size_t block_size, size_t obj_size, const void *obj,
+    void *id);
 
 /*********************/
 /* Package Variables */
 /*********************/
 
+/* Declare a free list to manage the H5HF_direct_t struct */
+H5FL_DEFINE(H5HF_direct_t);
+
+/* Declare a free list to manage the H5HF_direct_free_head_t struct */
+H5FL_DEFINE(H5HF_direct_free_head_t);
+
+/* Declare a free list to manage the H5HF_direct_free_node_t struct */
+H5FL_DEFINE(H5HF_direct_free_node_t);
+
 
 /*****************************/
 /* Library Private Variables */
@@ -73,9 +93,94 @@ H5FL_DEFINE_STATIC(H5HF_shared_t);
 
 
 /*-------------------------------------------------------------------------
- * Function:	H5HF_shared_init
+ * Function:	H5HF_shared_alloc
  *
- * Purpose:	Allocate & initialize shared fractal heap info
+ * Purpose:	Allocate shared fractal heap info 
+ *
+ * Return:	Non-negative on success/Negative on failure
+ *
+ * Programmer:	Quincey Koziol
+ *		koziol@ncsa.uiuc.edu
+ *		Feb 27 2006
+ *
+ *-------------------------------------------------------------------------
+ */
+H5HF_shared_t *
+H5HF_shared_alloc(H5F_t *f)
+{
+    H5HF_shared_t *shared = NULL;       /* Shared fractal heap information */
+    H5HF_shared_t *ret_value = NULL;    /* Return value */
+
+    FUNC_ENTER_NOAPI_NOINIT(H5HF_shared_alloc)
+
+    /*
+     * Check arguments.
+     */
+    HDassert(f);
+
+    /* Allocate space for the shared information */
+    if(NULL == (shared = H5FL_CALLOC(H5HF_shared_t)))
+	HGOTO_ERROR(H5E_RESOURCE, H5E_NOSPACE, NULL, "memory allocation failed for fractal heap shared information")
+
+    /* Set the internal parameters for the heap */
+    shared->f = f;
+
+    /* Set the return value */
+    ret_value = shared;
+
+done:
+    if(!ret_value)
+        if(shared)
+            H5HF_shared_free(shared);
+
+    FUNC_LEAVE_NOAPI(ret_value)
+} /* end H5HF_shared_alloc() */
+
+
+/*-------------------------------------------------------------------------
+ * Function:	H5HF_shared_own
+ *
+ * Purpose:	Have heap take ownership of the shared info
+ *
+ * Return:	Non-negative on success/Negative on failure
+ *
+ * Programmer:	Quincey Koziol
+ *		koziol@ncsa.uiuc.edu
+ *		Feb 27 2006
+ *
+ *-------------------------------------------------------------------------
+ */
+herr_t
+H5HF_shared_own(H5HF_t *fh, H5HF_shared_t *shared)
+{
+    herr_t ret_value = SUCCEED;           /* Return value */
+
+    FUNC_ENTER_NOAPI_NOINIT(H5HF_shared_own)
+
+    /*
+     * Check arguments.
+     */
+    HDassert(fh);
+    HDassert(shared);
+
+    /* Compute/cache some values */
+    shared->fixed_len_obj = (shared->fixed_len_size > 0);
+    shared->ref_count_obj = (shared->ref_count_size > 0);
+    shared->heap_off_size = H5HF_SIZEOF_OFFSET_BITS(shared->man_dtable_info.cparam.max_index);
+
+    /* Make shared heap info reference counted */
+    if(NULL == (fh->shared = H5RC_create(shared, H5HF_shared_free)))
+	HGOTO_ERROR(H5E_RESOURCE, H5E_NOSPACE, FAIL, "can't create ref-count wrapper for shared fractal heap info")
+
+done:
+    FUNC_LEAVE_NOAPI(ret_value)
+} /* end H5HF_shared_own() */
+
+
+/*-------------------------------------------------------------------------
+ * Function:	H5HF_shared_create
+ *
+ * Purpose:	Allocate & create shared fractal heap info for new heap
  *
  * Return:	Non-negative on success/Negative on failure
  *
@@ -86,24 +191,47 @@ H5FL_DEFINE_STATIC(H5HF_shared_t);
  *-------------------------------------------------------------------------
  */
 herr_t
-H5HF_shared_init(H5HF_t *fh, H5HF_create_t *cparam)
+H5HF_shared_create(H5F_t *f, H5HF_t *fh, haddr_t fh_addr, H5HF_create_t *cparam)
 {
     H5HF_shared_t *shared = NULL;       /* Shared fractal heap information */
     herr_t ret_value = SUCCEED;           /* Return value */
 
-    FUNC_ENTER_NOAPI_NOINIT(H5HF_shared_init)
+    FUNC_ENTER_NOAPI_NOINIT(H5HF_shared_create)
 
-    /* Allocate space for the shared information */
-    if(NULL == (shared = H5FL_CALLOC(H5HF_shared_t)))
-	HGOTO_ERROR(H5E_RESOURCE, H5E_NOSPACE, FAIL, "memory allocation failed for fractal heap shared information")
+    /*
+     * Check arguments.
+     */
+    HDassert(f);
+    HDassert(fh);
+    HDassert(cparam);
+
+#ifndef NDEBUG
+    /* Check for valid parameters */
+    if(!POWER_OF_TWO(cparam->managed.width) || cparam->managed.width == 0)
+	HGOTO_ERROR(H5E_HEAP, H5E_BADVALUE, FAIL, "width not power of two")
+    if(!POWER_OF_TWO(cparam->managed.start_block_size) || cparam->managed.start_block_size == 0)
+	HGOTO_ERROR(H5E_HEAP, H5E_BADVALUE, FAIL, "starting block size not power of two")
+    if(!POWER_OF_TWO(cparam->managed.max_direct_size) ||
+            (cparam->managed.max_direct_size == 0 || cparam->managed.max_direct_size > H5HL_MAX_DIRECT_SIZE_LIMIT))
+	HGOTO_ERROR(H5E_HEAP, H5E_BADVALUE, FAIL, "max. direct block size not power of two")
+    if(cparam->managed.max_index > (8 * H5F_SIZEOF_SIZE(f)) || cparam->managed.max_index == 0)
+	HGOTO_ERROR(H5E_HEAP, H5E_BADVALUE, FAIL, "max. direct block size not power of two")
+#endif /* NDEBUG */
+
+    /* Allocate & basic initialization for the shared info struct */
+    if(NULL == (shared = H5HF_shared_alloc(f)))
+	HGOTO_ERROR(H5E_RESOURCE, H5E_NOSPACE, FAIL, "can't allocate space for shared heap info")
 
     /* Set the creation parameters for the heap */
+    shared->heap_addr = fh_addr;
     shared->addrmap = cparam->addrmap;
     shared->standalone_size = cparam->standalone_size;
     shared->fixed_len_size = cparam->fixed_len_size;
+    shared->ref_count_size = cparam->ref_count_size;
+    HDmemcpy(&(shared->man_dtable_info.cparam), &(cparam->managed), sizeof(H5HF_dtable_cparam_t));
 
-    /* Make shared B-tree info reference counted */
-    if(NULL == (fh->shared = H5RC_create(shared, H5HF_shared_free)))
+    /* Make shared heap info reference counted */
+    if(H5HF_shared_own(fh, shared) < 0)
 	HGOTO_ERROR(H5E_RESOURCE, H5E_NOSPACE, FAIL, "can't create ref-count wrapper for shared fractal heap info")
 
 done:
@@ -112,7 +240,7 @@ done:
             H5HF_shared_free(shared);
 
     FUNC_LEAVE_NOAPI(ret_value)
-} /* end H5HF_shared_init() */
+} /* end H5HF_shared_create() */
 
 
 /*-------------------------------------------------------------------------
@@ -146,9 +274,9 @@ H5HF_shared_free(void *_shared)
 
 
 /*-------------------------------------------------------------------------
- * Function:	H5HF_alloc_end
+ * Function:	H5HF_man_alloc_end
  *
- * Purpose:	Allocate space for an object at the end of the heap
+ * Purpose:	Allocate space for an object at the end of the managed obj. heap
  *
  * Return:	Non-negative on success (with heap ID of new object
  *              filled in), negative on failure
@@ -160,38 +288,435 @@ H5HF_shared_free(void *_shared)
  *-------------------------------------------------------------------------
  */
 herr_t
-H5HF_man_alloc_end(H5HF_shared_t *shared, size_t size, const void *obj,
-    void *id/*out*/)
+H5HF_man_alloc_end(H5RC_t *fh_shared, hid_t dxpl_id, unsigned *fh_flags_ptr,
+    size_t size, const void *obj, void *id/*out*/)
 {
+    H5HF_shared_t *shared;              /* Shared heap information */
     herr_t ret_value = SUCCEED;
 
     FUNC_ENTER_NOAPI_NOINIT(H5HF_man_alloc_end)
+HDfprintf(stderr, "%s: size = %Zu\n", FUNC, size);
 
     /*
      * Check arguments.
      */
-    HDassert(shared);
+    HDassert(fh_shared);
+    HDassert(fh_flags_ptr);
     HDassert(size > 0);
     HDassert(obj);
     HDassert(id);
 
+    /* Get the pointer to the shared heap info */
+    shared = H5RC_GET_OBJ(fh_shared);
+    HDassert(shared);
+
     /* Check if this is the first object in the heap */
     if(shared->next_man_block == 0) {
-        if(size /* + H5HF_DIRECT_OVERHEAD */ <= shared->man_dtable_info.start_block_size) {
+        /* Check if the object can fit in a direct block of the starting block size */
+#ifdef QAK
+HDfprintf(stderr, "%s: H5HF_MAN_ABS_DIRECT_OVERHEAD_SIZE = %u\n", FUNC, H5HF_MAN_ABS_DIRECT_OVERHEAD_SIZE(shared, shared->man_dtable_info.cparam.start_block_size));
+HDfprintf(stderr, "%s: H5HF_MAN_ABS_DIRECT_OBJ_PREFIX_LEN_SIZE = %u\n", FUNC, H5HF_MAN_ABS_DIRECT_OBJ_PREFIX_LEN_SIZE(shared, shared->man_dtable_info.cparam.start_block_size));
+#endif /* QAK */
+        if((size + H5HF_MAN_ABS_DIRECT_OVERHEAD_SIZE(shared, shared->man_dtable_info.cparam.start_block_size)
+                    + H5HF_MAN_ABS_DIRECT_OBJ_PREFIX_LEN_SIZE(shared, shared->man_dtable_info.cparam.start_block_size))
+                <= shared->man_dtable_info.cparam.start_block_size) {
+            haddr_t dblock_addr;        /* Address of new direct block */
+            size_t dblock_size;         /* Size of new direct block */
+
+            /* Allocate initial direct block */
+            dblock_size = shared->man_dtable_info.cparam.start_block_size;
+            if(H5HF_man_dblock_create(fh_shared, dxpl_id, dblock_size, (hsize_t)0, &dblock_addr) < 0)
+                HGOTO_ERROR(H5E_RESOURCE, H5E_CANTALLOC, FAIL, "can't allocate fractal heap direct block")
+HDfprintf(stderr, "%s: dblock_addr = %a\n", FUNC, dblock_addr);
+
+            /* Point root at new direct block */
+            shared->next_man_block = dblock_size;
+            shared->man_dtable_info.curr_root_rows = 0;
+            shared->man_dtable_info.table_addr = dblock_addr;
+
+            /* Mark heap header as modified */
+            *fh_flags_ptr |= H5AC__DIRTIED_FLAG;
+
+            /* Attempt to insert object into direct block */
+            if(H5HF_man_dblock_insert(fh_shared, dxpl_id, dblock_addr, dblock_size, size, obj, id) < 0)
+                HGOTO_ERROR(H5E_RESOURCE, H5E_CANTALLOC, FAIL, "can't insert object into fractal heap direct block")
         } /* end if */
         else {
+HGOTO_ERROR(H5E_HEAP, H5E_UNSUPPORTED, FAIL, "first object doesn't fit into starting direct block")
         } /* end else */
-#ifdef QAK
-HDfprintf(stderr, "%s: size = %Zu\n", FUNC, size);
-HGOTO_ERROR(H5E_HEAP, H5E_UNSUPPORTED, FAIL, "allocating first object not supported yet")
-#endif /* QAK */
     } /* end if */
     else {
-HDfprintf(stderr, "%s: size = %Zu\n", FUNC, size);
 HGOTO_ERROR(H5E_HEAP, H5E_UNSUPPORTED, FAIL, "allocating objects at end of heap not supported yet")
     } /* end else */
 
 done:
     FUNC_LEAVE_NOAPI(ret_value)
-} /* end H5HF_alloc_end() */
+} /* end H5HF_man_alloc_end() */
+
+
+/*-------------------------------------------------------------------------
+ * Function:	H5HF_man_dblock_create
+ *
+ * Purpose:	Allocate & initialize a managed direct block
+ *
+ * Return:	Pointer to new direct block on success, NULL on failure
+ *
+ * Programmer:	Quincey Koziol
+ *		koziol@ncsa.uiuc.edu
+ *		Feb 27 2006
+ *
+ *-------------------------------------------------------------------------
+ */
+static herr_t
+H5HF_man_dblock_create(H5RC_t *fh_shared, hid_t dxpl_id, size_t block_size,
+    hsize_t block_off, haddr_t *addr_p)
+{
+    H5HF_direct_free_node_t *node;      /* Pointer to free list node for block */
+    H5HF_shared_t *shared;              /* Pointer to shared heap info */
+    H5HF_direct_t *dblock = NULL;       /* Pointer to direct block */
+    herr_t ret_value = SUCCEED;         /* Return value */
+
+    FUNC_ENTER_NOAPI_NOINIT(H5HF_man_dblock_create)
+
+    /*
+     * Check arguments.
+     */
+    HDassert(fh_shared);
+    HDassert(block_size > 0);
+    HDassert(addr_p);
+
+    /*
+     * Allocate file and memory data structures.
+     */
+    if(NULL == (dblock = H5FL_MALLOC(H5HF_direct_t)))
+	HGOTO_ERROR(H5E_RESOURCE, H5E_NOSPACE, FAIL, "memory allocation failed for fractal heap header")
+
+    /* Reset the metadata cache info for the heap header */
+    HDmemset(&dblock->cache_info, 0, sizeof(H5AC_info_t));
+
+    /* Share common heap information */
+    dblock->shared = fh_shared;
+    H5RC_INC(dblock->shared);
+
+    /* Get the pointer to the shared B-tree info */
+    shared = H5RC_GET_OBJ(dblock->shared);
+    HDassert(shared);
+
+    /* Set info for direct block */
+HDfprintf(stderr, "%s: size = %Zu, block_off = %Hu\n", FUNC, block_size, block_off);
+    dblock->size = block_size;
+    dblock->block_off = block_off;
+    dblock->blk_off_size = H5HF_SIZEOF_OFFSET_LEN(block_size);
+    dblock->free_list_head = H5HF_MAN_ABS_DIRECT_OVERHEAD_DBLOCK(shared, dblock);
+    dblock->blk_free_space = block_size - dblock->free_list_head;
+
+    /* Allocate buffer for block */
+/* XXX: Change to using free-list factories */
+    if((dblock->blk = H5FL_BLK_MALLOC(direct_block, block_size)) == NULL)
+        HGOTO_ERROR(H5E_RESOURCE, H5E_NOSPACE, FAIL, "memory allocation failed")
+#ifdef H5_USING_PURIFY
+HDmemset(dblock->blk, 0, dblock->size);
+#endif /* H5_USING_PURIFY */
+
+    /* Set up free list head */
+    if(NULL == (dblock->free_list = H5FL_MALLOC(H5HF_direct_free_head_t)))
+	HGOTO_ERROR(H5E_RESOURCE, H5E_NOSPACE, FAIL, "memory allocation failed for direct block free list head")
+    dblock->free_list->dirty = TRUE;
+
+    /* Set up free list node for all unused space in block */
+    if(NULL == (node = H5FL_MALLOC(H5HF_direct_free_node_t)))
+        HGOTO_ERROR(H5E_RESOURCE, H5E_NOSPACE, FAIL, "memory allocation failed for direct block free list node")
+
+    /* Set node's information */
+    node->size = dblock->blk_free_space;
+    node->my_offset = dblock->free_list_head;
+    node->next_offset = 0;
+    node->prev = node->next = NULL;
+
+    /* Attach to free list head */
+    dblock->free_list->first = node;
+
+    /* Allocate space for the header on disk */
+    if(HADDR_UNDEF == (*addr_p = H5MF_alloc(shared->f, H5FD_MEM_FHEAP_DBLOCK, dxpl_id, (hsize_t)block_size)))
+	HGOTO_ERROR(H5E_RESOURCE, H5E_NOSPACE, FAIL, "file allocation failed for fractal heap header")
+
+    /* Cache the new fractal heap header */
+    if(H5AC_set(shared->f, dxpl_id, H5AC_FHEAP_DBLOCK, *addr_p, dblock, H5AC__NO_FLAGS_SET) < 0)
+	HGOTO_ERROR(H5E_HEAP, H5E_CANTINIT, FAIL, "can't add fractal heap header to cache")
+
+done:
+    if(ret_value < 0)
+        if(dblock)
+            (void)H5HF_cache_dblock_dest(shared->f, dblock);
+
+    FUNC_LEAVE_NOAPI(ret_value)
+} /* end H5HF_man_dblock_create() */
+
+
+/*-------------------------------------------------------------------------
+ * Function:	H5HF_man_dblock_build_freelist
+ *
+ * Purpose:	Parse the free list information for a direct block and build
+ *              block's free list
+ *
+ * Return:	SUCCEED/FAIL
+ *
+ * Programmer:	Quincey Koziol
+ *		koziol@ncsa.uiuc.edu
+ *		Feb 28 2006
+ *
+ *-------------------------------------------------------------------------
+ */
+herr_t
+H5HF_man_dblock_build_freelist(H5HF_direct_t *dblock)
+{
+    H5HF_direct_free_head_t *head = NULL;       /* Pointer to free list head for block */
+    herr_t ret_value = SUCCEED;                 /* Return value */
+
+    FUNC_ENTER_NOAPI_NOINIT(H5HF_man_dblock_build_freelist)
+
+    /*
+     * Check arguments.
+     */
+    HDassert(dblock);
+
+    /* Allocate head of list */
+    if(NULL == (head = H5FL_MALLOC(H5HF_direct_free_head_t)))
+	HGOTO_ERROR(H5E_RESOURCE, H5E_NOSPACE, FAIL, "memory allocation failed for direct block free list head")
+    head->dirty = FALSE;
+
+    /* Check for any nodes on free list */
+    if(dblock->free_list_head == 0)
+        head->first = NULL;
+    else {
+        H5HF_direct_free_node_t *node = NULL;   /* Pointer to free list node for block */
+        H5HF_direct_free_node_t *prev_node;     /* Pointer to previous free list node for block */
+        hsize_t free_len;       /* Length of free list info */
+        hsize_t next_off;       /* Next node offset in block */
+        hsize_t prev_off;       /* Prev node offset in block */
+        uint8_t *p;             /* Temporary pointer to free node info */
+
+        /* Point to first node in free list */
+        p = dblock->blk + dblock->free_list_head;
+
+        /* Decode information for first node on free list */
+        UINT64DECODE_VAR(p, free_len, dblock->blk_off_size);
+        UINT64DECODE_VAR(p, next_off, dblock->blk_off_size);
+
+        /* Allocate node on list */
+        if(NULL == (node = H5FL_MALLOC(H5HF_direct_free_node_t)))
+            HGOTO_ERROR(H5E_RESOURCE, H5E_NOSPACE, FAIL, "memory allocation failed for direct block free list node")
+
+        /* Set node's information */
+        node->size = free_len;
+        node->my_offset = dblock->free_list_head;
+        node->next_offset = next_off;
+        node->prev = node->next = NULL;
+
+        /* Attach to free list head */
+        head->first = node;
+
+        /* Set up trailing node pointer */
+        prev_node = node;
+        prev_off = next_off;
+
+        /* Bring in rest of node on free list */
+        while(next_off != 0) {
+            /* Point to first node in free list */
+            p = dblock->blk + next_off;
+
+            /* Decode information for first node on free list */
+            UINT64DECODE_VAR(p, free_len, dblock->blk_off_size);
+            UINT64DECODE_VAR(p, next_off, dblock->blk_off_size);
+
+            /* Allocate node on list */
+            if(NULL == (node = H5FL_MALLOC(H5HF_direct_free_node_t)))
+                HGOTO_ERROR(H5E_RESOURCE, H5E_NOSPACE, FAIL, "memory allocation failed for direct block free list node")
+
+            /* Set node's information */
+            node->size = free_len;
+            node->my_offset = prev_off;
+            node->next_offset = next_off;
+            node->prev = prev_node;
+            node->next = NULL;
+
+            /* Update trailing info */
+            prev_node->next = node;
+            prev_off = next_off;
+
+            /* Advance to next node */
+            prev_node = node;
+        } /* end while */
+    } /* end else */
+
+    /* Assign free list head to block */
+    dblock->free_list = head;
+
+done:
+/* XXX: cleanup on failure? */
+    FUNC_LEAVE_NOAPI(ret_value)
+} /* end H5HF_man_dblock_build_freelist() */
+
+
+/*-------------------------------------------------------------------------
+ * Function:	H5HF_man_dblock_insert
+ *
+ * Purpose:	Allocate space in a managed direct block
+ *
+ * Return:	SUCCEED/FAIL
+ *
+ * Programmer:	Quincey Koziol
+ *		koziol@ncsa.uiuc.edu
+ *		Feb 28 2006
+ *
+ *-------------------------------------------------------------------------
+ */
+static herr_t
+H5HF_man_dblock_insert(H5RC_t *fh_shared, hid_t dxpl_id, haddr_t block_addr,
+    size_t block_size, size_t obj_size, const void *obj, void *id)
+{
+    H5HF_direct_t *dblock = NULL;       /* Pointer to direct block to modify */
+    H5HF_shared_t *shared;              /* Pointer to shared heap info */
+    herr_t ret_value = SUCCEED;         /* Return value */
+
+    FUNC_ENTER_NOAPI_NOINIT(H5HF_man_dblock_insert)
+
+    /*
+     * Check arguments.
+     */
+    HDassert(fh_shared);
+    HDassert(H5F_addr_defined(block_addr));
+    HDassert(block_size > 0);
+    HDassert(obj_size > 0);
+    HDassert(obj);
+    HDassert(id);
+
+    /* Get the pointer to the shared heap info */
+    shared = H5RC_GET_OBJ(fh_shared);
+    HDassert(shared);
+
+    /* Lock direct block */
+    if(NULL == (dblock = H5AC_protect(shared->f, dxpl_id, H5AC_FHEAP_DBLOCK, block_addr, &block_size, fh_shared, H5AC_WRITE)))
+        HGOTO_ERROR(H5E_HEAP, H5E_CANTPROTECT, FAIL, "unable to load fractal heap direct block")
+
+    /* Check for address mapping type */
+    if(shared->addrmap == H5HF_ABSOLUTE) {
+        H5HF_direct_free_node_t *node;      /* Pointer to free list node for block */
+        size_t full_obj_size;               /* Size of object including metadata */
+        size_t obj_off;                     /* Offset of object within block */
+        hbool_t found;                      /* Flag to indicate we found a node with enough free space */
+
+        /* Compute full object size, with metadata for object */
+        full_obj_size = obj_size + H5HF_MAN_ABS_DIRECT_OBJ_PREFIX_LEN_DBLOCK(shared, dblock);
+
+        /* Sanity check */
+        HDassert(dblock->blk_free_space >= full_obj_size);
+
+        /* Check for valid free list */
+        if(!dblock->free_list)
+            if(H5HF_man_dblock_build_freelist(dblock) < 0)
+                HGOTO_ERROR(H5E_HEAP, H5E_CANTDECODE, FAIL, "can't decode free list for block")
+        HDassert(dblock->free_list);
+
+        /* Search free list for block large enough to fit object */
+        node = dblock->free_list->first;
+        found = FALSE;
+        while(node) {
+            /* Check if this node is large enough to hold object */
+            if(node->size >= full_obj_size) {
+                /* Check for using exact free space available */
+                if(node->size == full_obj_size) {
+                    /* Set the offset of the object within the block */
+                    obj_off = node->my_offset;
+
+                    /* Check for allocating from first node in list */
+                    if(node->prev == NULL) {
+                        /* Make the next node in the free list the list head */
+                        dblock->free_list->first = node->next;
+                        dblock->free_list_head = node->next_offset;
+                    } /* end if */
+                    else {
+                        H5HF_direct_free_node_t *prev_node;          /* Pointer to previous free list node for block */
+
+                        /* Excise node from list */
+                        prev_node = node->prev;
+                        prev_node->next = node->next;
+                        if(node->next) {
+                            H5HF_direct_free_node_t *next_node;          /* Pointer to next free list node for block */
+
+                            next_node = node->next;
+                            next_node->prev = prev_node;
+                            prev_node->next_offset = next_node->my_offset;
+                        } /* end if */
+                        else
+                            prev_node->next_offset = 0;
+                    } /* end if */
+
+                    /* Release the memory for the free list node */
+                    H5FL_FREE(H5HF_direct_free_node_t, node);
+                } /* end if */
+                else {
+                    /* Allocate object from end of free space node */
+                    /* (so we don't have to play with the other node's info */
+                    obj_off = (node->my_offset + node->size) - full_obj_size;
+                    node->size -= full_obj_size;
+                } /* end else */
+
+                /* Reduce space available in block */
+                dblock->blk_free_space -= full_obj_size;
+
+                /* Mark free list as dirty */
+                dblock->free_list->dirty = TRUE;
+                found = TRUE;
+            } /* end if */
+
+            /* Avance to next node */
+            node = node->next;
+        } /* end while */
+
+        /* Encode metadata & copy object into block */
+        if(found) {
+            uint8_t *p;             /* Temporary pointer to obj info */
+
+            /* Point to location for object */
+HDfprintf(stderr, "%s: obj_off = %Zu\n", FUNC, obj_off);
+HDfprintf(stderr, "%s: full_obj_size = %Zu\n", FUNC, full_obj_size);
+            p = dblock->blk + obj_off;
+
+            /* Encode the length, if required */
+            if(!shared->fixed_len_obj)
+                UINT64ENCODE_VAR(p, obj_size, dblock->blk_off_size);
+
+            /* Encode a ref. count (of 1), if required */
+            if(shared->ref_count_obj)
+                UINT64ENCODE_VAR(p, 1, shared->ref_count_size);
+
+            /* Copy the object's data into the heap */
+            HDmemcpy(p, obj, obj_size);
+#ifndef NDEBUG
+            p += obj_size;
+#endif /* NDEBUG */
+
+            /* Sanity check */
+            HDassert((size_t)(p - (dblock->blk  + obj_off)) == full_obj_size);
+
+            /* Set the head ID for the new object */
+HDfprintf(stderr, "%s: dblock->block_off = %Hu\n", FUNC, dblock->block_off);
+            UINT64ENCODE_VAR(id, (dblock->block_off + obj_off), shared->heap_off_size);
+        } /* end if */
+        else
+            HGOTO_ERROR(H5E_RESOURCE, H5E_NOSPACE, FAIL, "no space for object in block")
+
+    } /* end if */
+    else {
+HGOTO_ERROR(H5E_HEAP, H5E_UNSUPPORTED, FAIL, "inserting within mapped managed blocks not supported yet")
+    } /* end else */
+
+done:
+    /* Release the direct block (marked as dirty) */
+    if(dblock && H5AC_unprotect(shared->f, dxpl_id, H5AC_FHEAP_DBLOCK, block_addr, dblock, H5AC__DIRTIED_FLAG) < 0)
+        HDONE_ERROR(H5E_HEAP, H5E_CANTUNPROTECT, FAIL, "unable to release fractal heap direct block")
+
+    FUNC_LEAVE_NOAPI(ret_value)
+} /* end H5HF_man_dblock_insert() */
 
diff --git a/src/H5HFpkg.h b/src/H5HFpkg.h
index 57671c0..6bb87df 100644
--- a/src/H5HFpkg.h
+++ b/src/H5HFpkg.h
@@ -44,21 +44,76 @@
 
 /* Fractal heap signatures */
 #define H5HF_HDR_MAGIC                  "FRHP"          /* Header */
+#define H5HF_DBLOCK_MAGIC               "FHDB"          /* Direct block */
 
-/* Size of the fractal heap header on disk */
-#define H5HF_HEADER_SIZE(f)     (                                             \
-    /* General metadata fields */                                             \
+/* "Standard" size of prefix information for fractal heap metadata */
+#define H5HF_METADATA_PREFIX_SIZE (                                           \
     4   /* Signature */                                                       \
     + 1 /* Version */                                                         \
     + 1 /* Metadata flags */                                                  \
     + 4 /* Metadata checksum */                                               \
+    )
+
+/* Size of doubling-table information */
+#define H5HF_DTABLE_INFO_SIZE(f) (                                            \
+    2   /* Width of table (i.e. # of columns) */                              \
+    + H5F_SIZEOF_SIZE(f) /* Starting block size */                            \
+    + H5F_SIZEOF_SIZE(f) /* Maximum direct block size */                      \
+    + 2 /* Max. size of heap (log2 of actual value - i.e. the # of bits) */   \
+    + 2 /* Starting # of rows in root indirect block */                       \
+    + H5F_SIZEOF_ADDR(f) /* File address of table managed */                  \
+    + 2 /* Current # of rows in root indirect block */                        \
+    )
+
+/* Size of the fractal heap header on disk */
+#define H5HF_HEADER_SIZE(f)     (                                             \
+    /* General metadata fields */                                             \
+    H5HF_METADATA_PREFIX_SIZE                                                 \
                                                                               \
     /* Fractal heap header specific fields */                                 \
     + 1 /* Address mapping */                                                 \
     + 4 /* Min. size of standalone object */                                  \
     + 4 /* Length of fixed-size objects */                                    \
+    + 1 /* Size of ref. count for objects */                                  \
+    + H5HF_DTABLE_INFO_SIZE(f) /* Size of managed obj. doubling-table info */ \
     )
 
+/* Size of header for each object in an absolute managed direct block */
+#define H5HF_MAN_ABS_DIRECT_OBJ_PREFIX_LEN_SIZE(s, o) (                       \
+    ((s)->fixed_len_obj ? 0 : H5HF_SIZEOF_OFFSET_LEN(o))  /* Length of object in block */ \
+    + (s)->ref_count_size       /* Ref. count of object in block */           \
+    )
+#define H5HF_MAN_ABS_DIRECT_OBJ_PREFIX_LEN_DBLOCK(s, d) (                     \
+    ((s)->fixed_len_obj ? 0 : (d)->blk_off_size)  /* Length of object in block */ \
+    + (s)->ref_count_size       /* Ref. count of object in block */           \
+    )
+
+/* Size of overhead for a direct block */
+#define H5HF_MAN_ABS_DIRECT_OVERHEAD_SIZE(s, o) (                             \
+    /* General metadata fields */                                             \
+    H5HF_METADATA_PREFIX_SIZE                                                 \
+                                                                              \
+    /* Fractal heap managed, absolutely mapped direct block specific fields */ \
+    + H5F_SIZEOF_ADDR((s)->f)   /* File address of heap owning the block */   \
+    + (s)->heap_off_size        /* Offset of the block in the heap */         \
+    + H5HF_SIZEOF_OFFSET_LEN(o) /* Total free space in a block */             \
+    + H5HF_SIZEOF_OFFSET_LEN(o) /* Offset of first descriptor in free list */ \
+    )
+#define H5HF_MAN_ABS_DIRECT_OVERHEAD_DBLOCK(s, d) (                           \
+    /* General metadata fields */                                             \
+    H5HF_METADATA_PREFIX_SIZE                                                 \
+                                                                              \
+    /* Fractal heap managed, absolutely mapped direct block specific fields */ \
+    + H5F_SIZEOF_ADDR((s)->f)   /* File address of heap owning the block */   \
+    + (s)->heap_off_size        /* Offset of the block in the heap */         \
+    + (d)->blk_off_size         /* Total free space in a block */             \
+    + (d)->blk_off_size         /* Offset of first descriptor in free list */ \
+    )
+
+/* Compute the # of bytes required to store an offset into a given buffer size */
+#define H5HF_SIZEOF_OFFSET_BITS(b)   (((b) + 7) / 8)
+#define H5HF_SIZEOF_OFFSET_LEN(l)   H5HF_SIZEOF_OFFSET_BITS(H5V_log2((unsigned)(l)))
+
 /****************************/
 /* Package Private Typedefs */
 /****************************/
@@ -66,16 +121,9 @@
 /* Doubling-table info */
 typedef struct H5HF_dtable_param_t {
     /* Immutable, pre-set information for table */
-    unsigned    width;          /* Number of columns in the table (must be power of 2) */
-    hsize_t     start_block_size; /* Starting block size for table (must be power of 2) */
-    hsize_t     max_direct_size; /* Maximum size of a direct block (must be power of 2) */
-    hsize_t     max_index;      /* Maximum ID/offset for table (must be power of 2) */
-    unsigned    start_root_rows;        /* Starting number of rows for root indirect block */
-                                /* 0 indicates to create the full indirect block for the root,
-                                 * right from the start.  Doesn't have to be power of 2
-                                 */
+    H5HF_dtable_cparam_t    cparam;     /* Creation parameters for table */
 
-    /* Derived information that varies during lifetime of table */
+    /* Derived information (varies during lifetime of table) */
     haddr_t     table_addr;     /* Address of first block for table */
                                 /* Undefined if no space allocated for table */
     unsigned    curr_root_rows; /* Current number of rows in the root indirect block */
@@ -89,12 +137,16 @@ typedef struct H5HF_dtable_param_t {
  * the instances of blocks in that fractal heap.
  */
 typedef struct H5HF_shared_t {
-    /* Shared internal information */
+    /* Shared internal information (varies during lifetime of heap) */
     hsize_t     next_man_block; /* Offset of next direct managed block */
     hsize_t     next_std_block; /* Offset of next direct standalone block */
     hsize_t     total_man_free; /* Total amount of free space in managed blocks */
     hsize_t     total_std_free; /* Total # of free standalone ID entries */
 
+    /* Cached/computed values */
+    haddr_t     heap_addr;      /* Address of heap header in the file */
+    H5F_t      *f;              /* Pointer to file for heap */
+
     /* Doubling table information */
     /* (Partially set by user, partially derived/updated internally) */
     H5HF_dtable_param_t man_dtable_info;        /* Doubling-table info for managed objects */
@@ -104,15 +156,17 @@ typedef struct H5HF_shared_t {
     H5HF_addrmap_t addrmap;     /* Type of address mapping */
     uint32_t standalone_size;   /* Size of object to store standalone */
     uint32_t fixed_len_size;    /* Size of objects (only for heaps w/fixed-length objects) */
+    unsigned char ref_count_size; /* Size of ref. count for objects (only for heaps w/ref. counted objects) */
 
     /* Information derived from user parameters */
     hbool_t     fixed_len_obj;  /* Are objects in the heap fixed length? */
     hbool_t     ref_count_obj;  /* Are objects in the heap ref. counted? */
     hbool_t     have_io_filter; /* Does the heap have I/O filters for the direct blocks? */
     hbool_t     write_once;     /* Is heap being written in "write once" mode? */
+    unsigned char heap_off_size; /* Size of heap offsets (in bytes) */
 } H5HF_shared_t;
 
-/* The fractal heap information */
+/* The fractal heap header information */
 typedef struct H5HF_t {
     /* Information for H5AC cache functions, _must_ be first field in structure */
     H5AC_info_t cache_info;
@@ -121,6 +175,39 @@ typedef struct H5HF_t {
     H5RC_t	*shared;	/* Ref-counted shared info	              */
 } H5HF_t;
 
+/* Direct block free list node */
+typedef struct H5HF_direct_free_node_t {
+    size_t      size;                           /* Size of free space */
+    size_t      my_offset;                      /* Offset of free space in block */
+    size_t      next_offset;                    /* Offset of next free space in block */
+    struct H5HF_direct_free_node_t *prev;       /* Previous node in free list */
+    struct H5HF_direct_free_node_t *next;       /* Next node in free list */
+} H5HF_direct_free_node_t;
+
+/* Direct block free list header */
+typedef struct H5HF_direct_free_head_t {
+    H5HF_direct_free_node_t *first;     /* First node in free list */
+    hbool_t dirty;                      /* Free list is modified */
+} H5HF_direct_free_head_t;
+
+/* A fractal heap direct block */
+typedef struct H5HF_direct_t {
+    /* Information for H5AC cache functions, _must_ be first field in structure */
+    H5AC_info_t cache_info;
+
+    /* Internal heap information */
+    H5RC_t	*shared;	/* Ref-counted shared info	              */
+    size_t      size;           /* Size of direct block                       */
+    size_t      blk_off_size;   /* Size of offsets in the block               */
+    H5HF_direct_free_head_t *free_list; /* Pointer to free list for block     */
+    uint8_t     *blk;           /* Pointer to buffer containing block data    */
+
+    /* Stored values */
+    hsize_t     block_off;      /* Offset of the block within the heap's address space */
+    size_t      blk_free_space; /* Total amount of free space in block        */
+    size_t      free_list_head; /* Offset of head of free list in block       */
+} H5HF_direct_t;
+
 
 /*****************************/
 /* Package Private Variables */
@@ -129,27 +216,49 @@ typedef struct H5HF_t {
 /* H5HF header inherits cache-like properties from H5AC */
 H5_DLLVAR const H5AC_class_t H5AC_FHEAP_HDR[1];
 
+/* H5HF direct block inherits cache-like properties from H5AC */
+H5_DLLVAR const H5AC_class_t H5AC_FHEAP_DBLOCK[1];
+
 /* Declare a free list to manage the H5HF_t struct */
 H5FL_EXTERN(H5HF_t);
 
+/* Declare a free list to manage the H5HF_direct_t struct */
+H5FL_EXTERN(H5HF_direct_t);
+
+/* Declare a free list to manage the H5HF_direct_free_head_t struct */
+H5FL_EXTERN(H5HF_direct_free_head_t);
+
+/* Declare a free list to manage the H5HF_direct_free_node_t struct */
+H5FL_EXTERN(H5HF_direct_free_node_t);
+
+/* Declare a free list to manage heap direct block data to/from disk */
+H5FL_BLK_EXTERN(direct_block);
+
+
 
 /******************************/
 /* Package Private Prototypes */
 /******************************/
 
 /* Routines for managing shared fractal heap info */
-H5_DLL herr_t H5HF_shared_init(H5HF_t *fh, H5HF_create_t *cparam);
+H5_DLL H5HF_shared_t * H5HF_shared_alloc(H5F_t *f);
+H5_DLL herr_t H5HF_shared_create(H5F_t *f, H5HF_t *fh, haddr_t heap_addr, H5HF_create_t *cparam);
+H5_DLL herr_t H5HF_shared_own(H5HF_t *fh, H5HF_shared_t *shared);
 
 /* Routines for allocating space */
-herr_t H5HF_man_alloc_end(H5HF_shared_t *shared, size_t size, const void *obj,
-    void *id/*out*/);
+H5_DLL herr_t H5HF_man_alloc_end(H5RC_t *fh_shared, hid_t dxpl_id, unsigned *fh_flags_ptr,
+    size_t size, const void *obj, void *id/*out*/);
+H5_DLL herr_t H5HF_man_dblock_build_freelist(H5HF_direct_t *dblock);
 
 /* Metadata cache callbacks */
-H5_DLL herr_t H5HF_cache_hdr_dest(H5F_t *f, H5HF_t *b);
+H5_DLL herr_t H5HF_cache_hdr_dest(H5F_t *f, H5HF_t *fh);
+H5_DLL herr_t H5HF_cache_dblock_dest(H5F_t *f, H5HF_direct_t *dblock);
 
 /* Debugging routines for dumping file structures */
 H5_DLL herr_t H5HF_hdr_debug(H5F_t *f, hid_t dxpl_id, haddr_t addr,
     FILE *stream, int indent, int fwidth);
+H5_DLL herr_t H5HF_dblock_debug(H5F_t *f, hid_t dxpl_id, haddr_t addr,
+    FILE *stream, int indent, int fwidth, haddr_t hdr_addr, unsigned nrec);
 
 /* Testing routines */
 #ifdef H5HF_TESTING
diff --git a/src/H5HFprivate.h b/src/H5HFprivate.h
index 62334fa..984d717 100644
--- a/src/H5HFprivate.h
+++ b/src/H5HFprivate.h
@@ -47,13 +47,28 @@ typedef enum {
     H5HF_MAPPED         /* The heap maps internal addresses to allow compaction */
 } H5HF_addrmap_t;
 
+/* Creation parameters for doubling-tables */
+typedef struct H5HF_dtable_cparam_t {
+    unsigned    width;          /* Number of columns in the table (must be power of 2) */
+    size_t      start_block_size; /* Starting block size for table (must be power of 2) */
+    size_t      max_direct_size; /* Maximum size of a direct block (must be power of 2) */
+    unsigned    max_index;      /* Maximum ID/offset for table (integer log2 of actual value, ie. the # of bits required) */
+    unsigned    start_root_rows;        /* Starting number of rows for root indirect block */
+                                /* 0 indicates to create the full indirect block for the root,
+                                 * right from the start.  Doesn't have to be power of 2
+                                 */
+} H5HF_dtable_cparam_t;
+
 /* Fractal heap creation parameters */
 typedef struct H5HF_create_t {
+    H5HF_dtable_cparam_t managed;/* Mapped object doubling-table creation parameters */
     H5HF_addrmap_t addrmap;     /* Type of address mapping for objects in heap */
     uint32_t standalone_size;   /* Size of object to store standalone */
                                 /* (i.e. max. size of object to manage) */
-    uint32_t fixed_len_size;    /* Size of objects (0 means variable-sized objects) */
+    uint32_t fixed_len_size;    /* Size of objects, in bytes (0 means variable-sized objects) */
                                 /* (only for heaps w/fixed-length objects) */
+    unsigned char ref_count_size; /* Size of ref. count field for objects, in bytes (0 means no ref. counts for objects) */
+                                /* (only for heaps w/ref. counted objects) */
 } H5HF_create_t;
 
 
diff --git a/src/H5HFtest.c b/src/H5HFtest.c
index ef14b2b..d17f804 100644
--- a/src/H5HFtest.c
+++ b/src/H5HFtest.c
@@ -103,6 +103,8 @@ H5HF_get_cparam_test(H5F_t *f, hid_t dxpl_id, haddr_t fh_addr, H5HF_create_t *cp
     cparam->addrmap = shared->addrmap;
     cparam->standalone_size = shared->standalone_size;
     cparam->fixed_len_size = shared->fixed_len_size;
+    cparam->ref_count_size = shared->ref_count_size;
+    HDmemcpy(&(cparam->managed), &(shared->man_dtable_info.cparam), sizeof(H5HF_dtable_cparam_t));
 
 done:
     /* Release fractal heap header node */
diff --git a/src/H5HLdbg.c b/src/H5HLdbg.c
index 0401f92..1dedaa5 100644
--- a/src/H5HLdbg.c
+++ b/src/H5HLdbg.c
@@ -125,44 +125,11 @@ H5HL_debug(H5F_t *f, hid_t dxpl_id, haddr_t addr, FILE * stream, int indent, int
 		"Percent of heap used:",
 		(100.0 * (double)(h->heap_alloc - amount_free) / (double)h->heap_alloc));
     }
+
     /*
      * Print the data in a VMS-style octal dump.
      */
-    fprintf(stream, "%*sData follows (`__' indicates free region)...\n",
-	    indent, "");
-    for (i=0; i<(int)(h->heap_alloc); i+=16) {
-	fprintf(stream, "%*s %8d: ", indent, "", i);
-	for (j = 0; j < 16; j++) {
-	    if (i+j<(int)(h->heap_alloc)) {
-		if (marker[i + j]) {
-		    fprintf(stream, "__ ");
-		} else {
-		    c = h->chunk[H5HL_SIZEOF_HDR(f) + i + j];
-		    fprintf(stream, "%02x ", c);
-		}
-	    } else {
-		fprintf(stream, "   ");
-	    }
-	    if (7 == j)
-		HDfputc(' ', stream);
-	}
-
-	for (j = 0; j < 16; j++) {
-	    if (i+j < (int)(h->heap_alloc)) {
-		if (marker[i + j]) {
-		    HDfputc(' ', stream);
-		} else {
-		    c = h->chunk[H5HL_SIZEOF_HDR(f) + i + j];
-		    if (c > ' ' && c < '~')
-			HDfputc(c, stream);
-		    else
-			HDfputc('.', stream);
-		}
-	    }
-	}
-
-	HDfputc('\n', stream);
-    }
+    H5_buffer_dump(stream, indent, h->chunk, marker, H5HL_SIZEOF_HDR(f), h->heap_alloc);
 
 done:
     if (h && H5AC_unprotect(f, dxpl_id, H5AC_LHEAP, addr, h, FALSE) != SUCCEED)
diff --git a/src/H5I.c b/src/H5I.c
index 00b8dad..7dbfce4 100644
--- a/src/H5I.c
+++ b/src/H5I.c
@@ -72,7 +72,6 @@
  * than the ID_MASK constant).
  */
 #  define H5I_LOC(a,s)		((hid_t)((size_t)(a)&((s)-1)))
-#  define POWER_OF_TWO(n)	((((n) - 1) & (n)) == 0 && (n) > 0)
 #else
 /*
  * Map an ID to a hash location.
diff --git a/src/H5Vprivate.h b/src/H5Vprivate.h
index 52f9d6b..55047cb 100644
--- a/src/H5Vprivate.h
+++ b/src/H5Vprivate.h
@@ -300,4 +300,35 @@ H5V_vector_inc(int n, hsize_t *v1, const hsize_t *v2)
     while (n--) *v1++ += *v2++;
 }
 
-#endif
+
+/*-------------------------------------------------------------------------
+ * Function:    H5V_power_of_two
+ *
+ * Purpose:     Determines the log base two of a number (i.e. log2(n)).
+ *
+ * Note:        N must be a power of two and is limited to 32-bit quantities.
+
+ *              This is from the "Bit Twiddling Hacks" at:
+ *                  http://graphics.stanford.edu/~seander/bithacks.html#IntegerLogDeBruijn
+ *
+ * Return:      log2(n) (always - no failure condition)
+ *
+ * Programmer:  Quincey Koziol
+ *              Monday, Febraury 27, 2006
+ *
+ *-------------------------------------------------------------------------
+ */
+static H5_inline unsigned 
+H5V_log2(unsigned n)
+{
+    static const unsigned MultiplyDeBruijnBitPosition[32] = 
+    {
+          0, 1, 28, 2, 29, 14, 24, 3, 30, 22, 20, 15, 25, 17, 4, 8, 
+            31, 27, 13, 23, 21, 19, 16, 7, 26, 12, 18, 6, 11, 5, 10, 9
+    };
+
+    return(MultiplyDeBruijnBitPosition[(n * 0x077CB531UL) >> 27]);
+} /* H5V_log2() */
+
+#endif /* H5Vprivate_H */
+
diff --git a/src/H5dbg.c b/src/H5dbg.c
new file mode 100644
index 0000000..8df83d3
--- /dev/null
+++ b/src/H5dbg.c
@@ -0,0 +1,142 @@
+/* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
+ * Copyright by the Board of Trustees of the University of Illinois.         *
+ * All rights reserved.                                                      *
+ *                                                                           *
+ * This file is part of HDF5.  The full HDF5 copyright notice, including     *
+ * terms governing use, modification, and redistribution, is contained in    *
+ * the files COPYING and Copyright.html.  COPYING can be found at the root   *
+ * of the source code distribution tree; Copyright.html can be found at the  *
+ * root level of an installed copy of the electronic HDF5 document set and   *
+ * is linked from the top-level documents page.  It can also be found at     *
+ * http://hdf.ncsa.uiuc.edu/HDF5/doc/Copyright.html.  If you do not have     *
+ * access to either file, you may request a copy from hdfhelp@ncsa.uiuc.edu. *
+ * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * */
+
+/*-------------------------------------------------------------------------
+ *
+ * Created:		H5dbg.c
+ *			Mar  4 2006
+ *			Quincey Koziol <koziol@ncsa.uiuc.edu>
+ *
+ * Purpose:		Generic debugging routines
+ *
+ *-------------------------------------------------------------------------
+ */
+
+/****************/
+/* Module Setup */
+/****************/
+
+/***********/
+/* Headers */
+/***********/
+#include "H5private.h"		/* Generic Functions			*/
+
+/****************/
+/* Local Macros */
+/****************/
+
+
+/******************/
+/* Local Typedefs */
+/******************/
+
+
+/********************/
+/* Local Prototypes */
+/********************/
+
+
+/*********************/
+/* Package Variables */
+/*********************/
+
+
+/*****************************/
+/* Library Private Variables */
+/*****************************/
+
+
+/*******************/
+/* Local Variables */
+/*******************/
+
+
+
+/*-------------------------------------------------------------------------
+ * Function:	H5_buffer_dump
+ *
+ * Purpose:	Dumps a buffer of memory in an octal dump form
+ *
+ * Return:	Non-negative on success/Negative on failure
+ *
+ * Programmer:	Quincey Koziol
+ *		koziol@ncsa.uiuc.edu
+ *		Mar  4 2006
+ *
+ *-------------------------------------------------------------------------
+ */
+herr_t
+H5_buffer_dump(FILE *stream, int indent, uint8_t *buf,
+    uint8_t *marker, size_t buf_offset, size_t buf_size)
+{
+    size_t	u, v;                   /* Local index variable */
+
+    FUNC_ENTER_NOAPI_NOINIT_NOFUNC(H5_buffer_dump)
+
+    /*
+     * Check arguments.
+     */
+    HDassert(stream);
+    HDassert(indent >= 0);
+    HDassert(buf);
+    HDassert(marker);
+    HDassert(buf_size > 0);
+
+    /*
+     * Print the buffer in a VMS-style octal dump.
+     */
+    HDfprintf(stream, "%*sData follows (`__' indicates free region)...\n",
+	    indent, "");
+    for(u = 0; u < buf_size; u += 16) {
+        uint8_t		c;
+
+	HDfprintf(stream, "%*s %8d: ", indent, "", u);
+
+        /* Print the hex values */
+	for(v = 0; v < 16; v++) {
+	    if(u + v < buf_size) {
+		if(marker[u + v])
+		    HDfprintf(stream, "__ ");
+		else {
+		    c = buf[buf_offset + u + v];
+		    HDfprintf(stream, "%02x ", c);
+		} /* end else */
+	    } /* end if */
+            else
+		fprintf(stream, "   ");
+	    if(7 == v)
+		HDfputc(' ', stream);
+	} /* end for */
+
+        /* Print the character values */
+	for(v = 0; v < 16; v++) {
+	    if(u + v < buf_size) {
+		if(marker[u + v])
+		    HDfputc(' ', stream);
+		else {
+		    c = buf[buf_offset + u + v];
+		    if(HDisprint(c))
+			HDfputc(c, stream);
+		    else
+			HDfputc('.', stream);
+		} /* end else */
+	    } /* end if */
+	} /* end for */
+
+	HDfputc('\n', stream);
+    } /* end for */
+
+    FUNC_LEAVE_NOAPI(SUCCEED)
+} /* end H5_buffer_dump() */
+
diff --git a/src/H5private.h b/src/H5private.h
index 1b904e3..e7f339b 100644
--- a/src/H5private.h
+++ b/src/H5private.h
@@ -325,6 +325,9 @@
 #   define SIGN(a)		((a)>0 ? 1 : (a)<0 ? -1 : 0)
 #endif
 
+/* test for number that is a power of 2 */
+#  define POWER_OF_TWO(n)	((((n) - 1) & (n)) == 0 && (n) > 0)
+
 /*
  * HDF Boolean type.
  */
@@ -1411,5 +1414,9 @@ H5_DLL int H5S_term_interface(void);
 H5_DLL int H5T_term_interface(void);
 H5_DLL int H5Z_term_interface(void);
 
+/* Functions for debugging */
+H5_DLL herr_t H5_buffer_dump(FILE *stream, int indent, uint8_t *buf,
+    uint8_t *marker, size_t buf_offset, size_t buf_size);
+
 #endif
 
diff --git a/src/Makefile.am b/src/Makefile.am
index 0a3abbf..d6ebcfb 100755
--- a/src/Makefile.am
+++ b/src/Makefile.am
@@ -37,7 +37,7 @@ libhdf5_la_LDFLAGS= -version-info $(LT_VERS_INTERFACE):$(LT_VERS_REVISION):$(LT_
 MOSTLYCLEANFILES=H5Tinit.c
 
 # library sources
-libhdf5_la_SOURCES= H5.c H5A.c H5AC.c H5B.c H5Bcache.c \
+libhdf5_la_SOURCES= H5.c H5dbg.c H5A.c H5AC.c H5B.c H5Bcache.c \
         H5B2.c H5B2cache.c H5B2dbg.c H5B2int.c H5B2test.c \
         H5C.c \
         H5D.c \
diff --git a/src/Makefile.in b/src/Makefile.in
index b7914e1..8ef4320 100644
--- a/src/Makefile.in
+++ b/src/Makefile.in
@@ -82,13 +82,13 @@ am__installdirs = "$(DESTDIR)$(libdir)" "$(DESTDIR)$(settingsdir)" \
 libLTLIBRARIES_INSTALL = $(INSTALL)
 LTLIBRARIES = $(lib_LTLIBRARIES)
 libhdf5_la_LIBADD =
-am_libhdf5_la_OBJECTS = H5.lo H5A.lo H5AC.lo H5B.lo H5Bcache.lo \
-	H5B2.lo H5B2cache.lo H5B2dbg.lo H5B2int.lo H5B2test.lo H5C.lo \
-	H5D.lo H5Dcompact.lo H5Dcontig.lo H5Defl.lo H5Dio.lo \
-	H5Distore.lo H5Dmpio.lo H5Doh.lo H5Dselect.lo H5Dtest.lo \
-	H5E.lo H5F.lo H5Fdbg.lo H5Fmount.lo H5Fsfile.lo H5Fsuper.lo \
-	H5FD.lo H5FDcore.lo H5FDfamily.lo H5FDfphdf5.lo H5FDlog.lo \
-	H5FDmpi.lo H5FDmpio.lo H5FDmpiposix.lo H5FDmulti.lo \
+am_libhdf5_la_OBJECTS = H5.lo H5dbg.lo H5A.lo H5AC.lo H5B.lo \
+	H5Bcache.lo H5B2.lo H5B2cache.lo H5B2dbg.lo H5B2int.lo \
+	H5B2test.lo H5C.lo H5D.lo H5Dcompact.lo H5Dcontig.lo H5Defl.lo \
+	H5Dio.lo H5Distore.lo H5Dmpio.lo H5Doh.lo H5Dselect.lo \
+	H5Dtest.lo H5E.lo H5F.lo H5Fdbg.lo H5Fmount.lo H5Fsfile.lo \
+	H5Fsuper.lo H5FD.lo H5FDcore.lo H5FDfamily.lo H5FDfphdf5.lo \
+	H5FDlog.lo H5FDmpi.lo H5FDmpio.lo H5FDmpiposix.lo H5FDmulti.lo \
 	H5FDsec2.lo H5FDstdio.lo H5FDstream.lo H5FL.lo H5FO.lo H5FP.lo \
 	H5FPclient.lo H5FPserver.lo H5FS.lo H5G.lo H5Gent.lo \
 	H5Glink.lo H5Gloc.lo H5Gname.lo H5Gnode.lo H5Gobj.lo H5Goh.lo \
@@ -389,7 +389,7 @@ libhdf5_la_LDFLAGS = -version-info $(LT_VERS_INTERFACE):$(LT_VERS_REVISION):$(LT
 MOSTLYCLEANFILES = H5Tinit.c
 
 # library sources
-libhdf5_la_SOURCES = H5.c H5A.c H5AC.c H5B.c H5Bcache.c \
+libhdf5_la_SOURCES = H5.c H5dbg.c H5A.c H5AC.c H5B.c H5Bcache.c \
         H5B2.c H5B2cache.c H5B2dbg.c H5B2int.c H5B2test.c \
         H5C.c \
         H5D.c \
@@ -702,6 +702,7 @@ distclean-compile:
 @AMDEP_TRUE@@am__include@ @am__quote@./$(DEPDIR)/H5Zshuffle.Plo@am__quote@
 @AMDEP_TRUE@@am__include@ @am__quote@./$(DEPDIR)/H5Zszip.Plo@am__quote@
 @AMDEP_TRUE@@am__include@ @am__quote@./$(DEPDIR)/H5Ztrans.Plo@am__quote@
+@AMDEP_TRUE@@am__include@ @am__quote@./$(DEPDIR)/H5dbg.Plo@am__quote@
 @AMDEP_TRUE@@am__include@ @am__quote@./$(DEPDIR)/H5detect-H5detect.Po@am__quote@
 
 .c.o:
diff --git a/test/fheap.c b/test/fheap.c
index 1a9f8e9..3aaa7e8 100644
--- a/test/fheap.c
+++ b/test/fheap.c
@@ -28,6 +28,17 @@
 /* Other private headers that this test requires */
 #include "H5Iprivate.h"
 
+/* "Standard" creation table parameters */
+#define STD_ADDRMAP     H5HF_ABSOLUTE           /* Heap address mapping */
+#define STD_STAND_SIZE  (64 * 1024)             /* Standalone obj. min. size */
+#define STD_FIXED_LEN_SIZE 0                    /* Fixed length obj. size */
+#define STD_REF_COUNT_SIZE 0                    /* Size of ref. count for obj. */
+#define STD_MAN_WIDTH   32                      /* Managed obj. table width */
+#define STD_MAN_START_BLOCK_SIZE 1024           /* Managed obj. starting block size */
+#define STD_MAN_MAX_DIRECT_SIZE (1024 * 1024)   /* Managed obj. max. direct block size */
+#define STD_MAN_MAX_INDEX 64                    /* Managed obj. # of bits for total heap size */
+#define STD_MAN_START_ROOT_ROWS 1               /* Managed obj. starting # of root indirect block rows */
+
 const char *FILENAME[] = {
     "fheap",
     NULL
@@ -35,6 +46,44 @@ const char *FILENAME[] = {
 
 
 /*-------------------------------------------------------------------------
+ * Function:	init_std_cparam
+ *
+ * Purpose:	Initialize heap creation parameter structure with standard
+ *              settings
+ *
+ * Return:	Success:	0
+ *
+ *		Failure:	1
+ *
+ * Programmer:	Quincey Koziol
+ *              Monday, February 27, 2006
+ *
+ *-------------------------------------------------------------------------
+ */
+static int
+init_std_cparam(H5HF_create_t *cparam)
+{
+    /* Wipe out background */
+    HDmemset(cparam, 0, sizeof(H5HF_create_t));
+
+    /* General parameters */
+    cparam->addrmap = STD_ADDRMAP;
+    cparam->standalone_size = STD_STAND_SIZE;
+    cparam->fixed_len_size = STD_FIXED_LEN_SIZE;
+    cparam->ref_count_size = STD_REF_COUNT_SIZE;
+
+    /* Managed object doubling-table parameters */
+    cparam->managed.width = STD_MAN_WIDTH;
+    cparam->managed.start_block_size = STD_MAN_START_BLOCK_SIZE;
+    cparam->managed.max_direct_size = STD_MAN_MAX_DIRECT_SIZE;
+    cparam->managed.max_index = STD_MAN_MAX_INDEX;
+    cparam->managed.start_root_rows = STD_MAN_START_ROOT_ROWS;
+
+    return(0);
+} /* init_std_cparam() */
+
+
+/*-------------------------------------------------------------------------
  * Function:	test_create
  *
  * Purpose:	Create fractal heap
@@ -72,9 +121,7 @@ test_create(hid_t fapl)
      * Test fractal heap creation (w/absolute address mapping)
      */
     TESTING("Fractal heap creation (w/absolute address mapping)");
-    cparam.addrmap = H5HF_ABSOLUTE;
-    cparam.standalone_size = 64 * 1024;
-    cparam.fixed_len_size = 0;
+    init_std_cparam(&cparam);
     if(H5HF_create(f, H5P_DATASET_XFER_DEFAULT, &cparam, &fh_addr/*out*/) < 0)
         FAIL_STACK_ERROR
     if(!H5F_addr_defined(fh_addr))
@@ -94,9 +141,8 @@ test_create(hid_t fapl)
      * Test fractal heap creation (w/mapped address mapping)
      */
     TESTING("Fractal heap creation (w/mapped address mapping)");
+    init_std_cparam(&cparam);
     cparam.addrmap = H5HF_MAPPED;
-    cparam.standalone_size = 64 * 1024;
-    cparam.fixed_len_size = 0;
     if(H5HF_create(f, H5P_DATASET_XFER_DEFAULT, &cparam, &fh_addr/*out*/) < 0)
         FAIL_STACK_ERROR
     if(!H5F_addr_defined(fh_addr))
@@ -151,7 +197,7 @@ test_abs_insert_first(hid_t fapl)
     H5HF_create_t cparam;               /* Creation parameters for heap */
     haddr_t     fh_addr;                /* Address of fractal heap created */
     unsigned char obj[10];              /* Buffer for object to insert */
-    haddr_t     heap_id;                /* Heap ID for object inserted */
+    hsize_t     heap_id;                /* Heap ID for object inserted */
     unsigned    u;                      /* Local index variable */
     herr_t      ret;                    /* Generic error return value */
 
@@ -167,14 +213,12 @@ test_abs_insert_first(hid_t fapl)
         STACK_ERROR
 
     /* Create absolute heap */
-    cparam.addrmap = H5HF_ABSOLUTE;
-    cparam.standalone_size = 64 * 1024;
-    cparam.fixed_len_size = 0;
+    init_std_cparam(&cparam);
     if(H5HF_create(f, dxpl, &cparam, &fh_addr/*out*/) < 0)
         FAIL_STACK_ERROR
     if(!H5F_addr_defined(fh_addr))
         FAIL_STACK_ERROR
-#ifdef QAK
+#ifndef QAK
 HDfprintf(stdout, "Fractal heap header address = %a\n", fh_addr);
 #endif /* QAK */
 
@@ -186,11 +230,11 @@ HDfprintf(stdout, "Fractal heap header address = %a\n", fh_addr);
      * Test inserting first (small) object into absolute heap
      */
     TESTING("Inserting first (small) object into absolute heap");
-    heap_id = HADDR_UNDEF;
+    heap_id = 0;
     if(H5HF_insert(f, dxpl, fh_addr, sizeof(obj), obj, &heap_id) < 0)
         FAIL_STACK_ERROR
-#ifdef QAK
-HDfprintf(stdout, "heap_id = %a\n", heap_id);
+#ifndef QAK
+HDfprintf(stdout, "heap_id = %Hu\n", heap_id);
 #endif /* QAK */
     PASSED()
 
@@ -242,7 +286,7 @@ main(void)
     if(nerrors)
         goto error;
     puts("All fractal heap tests passed.");
-#ifndef QAK
+#ifdef QAK
     h5_cleanup(FILENAME, fapl);
 #else /* QAK */
 HDfprintf(stderr, "Uncomment cleanup!\n");
diff --git a/tools/misc/h5debug.c b/tools/misc/h5debug.c
index b93ec2a..ca26c5d 100644
--- a/tools/misc/h5debug.c
+++ b/tools/misc/h5debug.c
@@ -74,19 +74,18 @@ main(int argc, char *argv[])
 {
     hid_t	fid, fapl, dxpl;
     H5F_t       *f;
-    haddr_t     addr=0, extra=0, extra2=0;
+    haddr_t     addr = 0, extra = 0, extra2 = 0;
     uint8_t     sig[SIGLEN];
-    int         i;
+    size_t      u;
     herr_t      status = SUCCEED;
 
-    if (argc == 1) {
-	fprintf(stderr,
-		"Usage: %s filename [signature-addr [extra]]\n", argv[0]);
+    if(argc == 1) {
+	fprintf(stderr, "Usage: %s filename [signature-addr [extra]]\n", argv[0]);
 	HDexit(1);
     }
 
     /* Initialize the library */
-    if(H5open ()<0) {
+    if(H5open() < 0) {
         fprintf(stderr, "cannot initialize the library\n");
         HDexit(1);
     }
@@ -102,14 +101,13 @@ main(int argc, char *argv[])
         fprintf(stderr, "cannot create file access property list\n");
         HDexit(1);
     }
-    if (strchr (argv[1], '%')) {
+    if(strchr (argv[1], '%'))
 	H5Pset_fapl_family (fapl, (hsize_t)0, H5P_DEFAULT);
-    }
-    if ((fid = H5Fopen(argv[1], H5F_ACC_RDONLY, fapl)) < 0) {
+    if((fid = H5Fopen(argv[1], H5F_ACC_RDONLY, fapl)) < 0) {
         fprintf(stderr, "cannot open file\n");
         HDexit(1);
     }
-    if (NULL == (f = H5I_object(fid))) {
+    if(NULL == (f = H5I_object(fid))) {
         fprintf(stderr, "cannot obtain H5F_t pointer\n");
         HDexit(2);
     }
@@ -117,46 +115,46 @@ main(int argc, char *argv[])
     /*
      * Parse command arguments.
      */
-    if (argc > 2)
+    if(argc > 2)
         addr = HDstrtoll(argv[2], NULL, 0);
-    if (argc > 3)
+    if(argc > 3)
         extra = HDstrtoll(argv[3], NULL, 0);
-    if (argc > 4)
+    if(argc > 4)
         extra2 = HDstrtoll(argv[4], NULL, 0);
 
     /*
      * Read the signature at the specified file position.
      */
     HDfprintf(stdout, "Reading signature at address %a (rel)\n", addr);
-    if (H5F_block_read(f, H5FD_MEM_SUPER, addr, sizeof(sig), dxpl, sig)<0) {
+    if(H5F_block_read(f, H5FD_MEM_SUPER, addr, sizeof(sig), dxpl, sig) < 0) {
         fprintf(stderr, "cannot read signature\n");
         HDexit(3);
     }
-    if (!HDmemcmp(sig, H5F_SIGNATURE, H5F_SIGNATURE_LEN)) {
+    if(!HDmemcmp(sig, H5F_SIGNATURE, H5F_SIGNATURE_LEN)) {
         /*
          * Debug the file's super block.
          */
         status = H5F_debug(f, H5P_DATASET_XFER_DEFAULT, stdout, 0, VCOL);
 
-    } else if (!HDmemcmp(sig, H5HL_MAGIC, H5HL_SIZEOF_MAGIC)) {
+    } else if(!HDmemcmp(sig, H5HL_MAGIC, H5HL_SIZEOF_MAGIC)) {
         /*
          * Debug a local heap.
          */
         status = H5HL_debug(f, H5P_DATASET_XFER_DEFAULT, addr, stdout, 0, VCOL);
 
-    } else if (!HDmemcmp (sig, H5HG_MAGIC, H5HG_SIZEOF_MAGIC)) {
+    } else if(!HDmemcmp (sig, H5HG_MAGIC, H5HG_SIZEOF_MAGIC)) {
 	/*
 	 * Debug a global heap collection.
 	 */
 	status = H5HG_debug (f, H5P_DATASET_XFER_DEFAULT, addr, stdout, 0, VCOL);
 
-    } else if (!HDmemcmp(sig, H5G_NODE_MAGIC, H5G_NODE_SIZEOF_MAGIC)) {
+    } else if(!HDmemcmp(sig, H5G_NODE_MAGIC, H5G_NODE_SIZEOF_MAGIC)) {
         /*
          * Debug a symbol table node.
          */
         status = H5G_node_debug(f, H5P_DATASET_XFER_DEFAULT, addr, stdout, 0, VCOL, extra);
 
-    } else if (!HDmemcmp(sig, H5B_MAGIC, H5B_SIZEOF_MAGIC)) {
+    } else if(!HDmemcmp(sig, H5B_MAGIC, H5B_SIZEOF_MAGIC)) {
         /*
          * Debug a B-tree.  B-trees are debugged through the B-tree
          * subclass.  The subclass identifier is the byte immediately
@@ -165,7 +163,7 @@ main(int argc, char *argv[])
         H5B_subid_t subtype = (H5B_subid_t)sig[H5B_SIZEOF_MAGIC];
         unsigned    ndims;
 
-        switch (subtype) {
+        switch(subtype) {
             case H5B_SNODE_ID:
                 status = H5G_node_debug(f, H5P_DATASET_XFER_DEFAULT, addr, stdout, 0, VCOL, extra);
                 break;
@@ -180,7 +178,7 @@ main(int argc, char *argv[])
                 HDexit(4);
         }
 
-    } else if (!HDmemcmp(sig, H5B2_HDR_MAGIC, H5B2_SIZEOF_MAGIC)) {
+    } else if(!HDmemcmp(sig, H5B2_HDR_MAGIC, H5B2_SIZEOF_MAGIC)) {
         /*
          * Debug a v2 B-tree.  B-trees are debugged through the B-tree
          * subclass.  The subclass identifier is two bytes after the
@@ -188,7 +186,7 @@ main(int argc, char *argv[])
          */
         H5B2_subid_t subtype = (H5B2_subid_t)sig[H5B2_SIZEOF_MAGIC+1];
 
-        switch (subtype) {
+        switch(subtype) {
             case H5B2_TEST_ID:
                 status = H5B2_hdr_debug(f, H5P_DATASET_XFER_DEFAULT, addr, stdout, 0, VCOL, H5B2_TEST);
                 break;
@@ -198,7 +196,7 @@ main(int argc, char *argv[])
                 HDexit(4);
         } /* end switch */
 
-    } else if (!HDmemcmp(sig, H5B2_INT_MAGIC, H5B2_SIZEOF_MAGIC)) {
+    } else if(!HDmemcmp(sig, H5B2_INT_MAGIC, H5B2_SIZEOF_MAGIC)) {
         /*
          * Debug a v2 B-tree.  B-trees are debugged through the B-tree
          * subclass.  The subclass identifier is two bytes after the
@@ -206,7 +204,7 @@ main(int argc, char *argv[])
          */
         H5B2_subid_t subtype = (H5B2_subid_t)sig[H5B2_SIZEOF_MAGIC+1];
 
-        switch (subtype) {
+        switch(subtype) {
             case H5B2_TEST_ID:
                 status = H5B2_int_debug(f, H5P_DATASET_XFER_DEFAULT, addr, stdout, 0, VCOL, H5B2_TEST, extra, (unsigned)extra2);
                 break;
@@ -216,7 +214,7 @@ main(int argc, char *argv[])
                 HDexit(4);
         } /* end switch */
 
-    } else if (!HDmemcmp(sig, H5B2_LEAF_MAGIC, H5B2_SIZEOF_MAGIC)) {
+    } else if(!HDmemcmp(sig, H5B2_LEAF_MAGIC, H5B2_SIZEOF_MAGIC)) {
         /*
          * Debug a v2 B-tree.  B-trees are debugged through the B-tree
          * subclass.  The subclass identifier is two bytes after the
@@ -224,7 +222,7 @@ main(int argc, char *argv[])
          */
         H5B2_subid_t subtype = (H5B2_subid_t)sig[H5B2_SIZEOF_MAGIC+1];
 
-        switch (subtype) {
+        switch(subtype) {
             case H5B2_TEST_ID:
                 status = H5B2_leaf_debug(f, H5P_DATASET_XFER_DEFAULT, addr, stdout, 0, VCOL, H5B2_TEST, extra, (unsigned)extra2);
                 break;
@@ -234,13 +232,19 @@ main(int argc, char *argv[])
                 HDexit(4);
         } /* end switch */
 
-    } else if (!HDmemcmp(sig, H5HF_HDR_MAGIC, H5HF_SIZEOF_MAGIC)) {
+    } else if(!HDmemcmp(sig, H5HF_HDR_MAGIC, H5HF_SIZEOF_MAGIC)) {
         /*
          * Debug a fractal heap header.
          */
         status = H5HF_hdr_debug(f, H5P_DATASET_XFER_DEFAULT, addr, stdout, 0, VCOL);
 
-    } else if (sig[0] == H5O_VERSION) {
+    } else if(!HDmemcmp(sig, H5HF_DBLOCK_MAGIC, H5HF_SIZEOF_MAGIC)) {
+        /*
+         * Debug a fractal heap direct block.
+         */
+        status = H5HF_dblock_debug(f, H5P_DATASET_XFER_DEFAULT, addr, stdout, 0, VCOL, extra, (size_t)extra2);
+
+    } else if(sig[0] == H5O_VERSION) {
         /*
          * This could be an object header.  Since they don't have a signature
          * it's a somewhat "ify" detection.
@@ -252,15 +256,14 @@ main(int argc, char *argv[])
          * Got some other unrecognized signature.
          */
         printf("%-*s ", VCOL, "Signature:");
-        for (i = 0; i < sizeof(sig); i++) {
-            if (sig[i] > ' ' && sig[i] <= '~' && '\\' != sig[i]) {
-                HDputchar(sig[i]);
-            } else if ('\\' == sig[i]) {
+        for (u = 0; u < sizeof(sig); u++) {
+            if (sig[u] > ' ' && sig[u] <= '~' && '\\' != sig[u])
+                HDputchar(sig[u]);
+            else if ('\\' == sig[u]) {
                 HDputchar('\\');
                 HDputchar('\\');
-            } else {
-                printf("\\%03o", sig[i]);
-            }
+            } else
+                printf("\\%03o", sig[u]);
         }
         HDputchar('\n');
 
@@ -268,11 +271,12 @@ main(int argc, char *argv[])
         HDexit(4);
     }
 
-    if (status < 0) {
+    if(status < 0) {
         fprintf(stderr, "An error occurred!\n");
         H5Eprint(stderr);
         HDexit(5);
     }
+
     H5Pclose(dxpl);
     H5Pclose(fapl);
     H5Fclose(fid);