[svn-r9764] Purpose:

    New feature

Description:
    Add some additional features to the skip list code that was needed to
fully support all the features that the threaded, balanced binary tree code
has.

    Also, updated the property list code to take advantage of a few of the
new features.

Platforms tested:
    FreeBSD 4.10 (sleipnir)
    Too minor to require h5committest

1 files changed, 667 insertions, 110 deletions

diff --git a/src/H5SL.c b/src/H5SL.c
index 7a54b14..005cb86 100644
--- a/src/H5SL.c
+++ b/src/H5SL.c
@@ -32,6 +32,9 @@
  *               search by position) in section 3.4 of "A Skip List Cookbook",
  *               but they shouldn't be that hard to add, if necessary)
  *
+ *              (This implementation has an additional backward pointer, which
+ *               allows the list to be iterated in reverse)
+ *
  */
 
 /* Interface initialization */
@@ -50,12 +53,12 @@
 
 /* Local Macros */
 
-/* Define the code template for insertions for the "OP" in the H5SL_FIND macro */
-#define H5SL_FIND_INSERT_FOUND(SLIST,X,UPDATE,I,ITEM)                   \
-        HGOTO_ERROR(H5E_SLIST,H5E_CANTINSERT,FAIL,"can't insert duplicate key");
+/* Define the code template for insertions for the "OP" in the H5SL_LOCATE macro */
+#define H5SL_LOCATE_INSERT_FOUND(SLIST,X,UPDATE,I,ITEM)                   \
+        HGOTO_ERROR(H5E_SLIST,H5E_CANTINSERT,NULL,"can't insert duplicate key");
 
-/* Define the code template for removals for the "OP" in the H5SL_FIND macro */
-#define H5SL_FIND_REMOVE_FOUND(SLIST,X,UPDATE,I,ITEM)                   \
+/* Define the code template for removals for the "OP" in the H5SL_LOCATE macro */
+#define H5SL_LOCATE_REMOVE_FOUND(SLIST,X,UPDATE,I,ITEM)                   \
         void *tmp;                                                      \
                                                                         \
         for(I=0; I<=(int)SLIST->curr_level; I++) {                      \
@@ -63,6 +66,10 @@
                 break;                                                  \
             *UPDATE[I]=X->forward[I];                                   \
         } /* end for */                                                 \
+        if(SLIST->last==X)                                              \
+            SLIST->last=X->backward;                                    \
+        else                                                            \
+            X->forward[0]->backward=X->backward;                        \
         tmp=X->item;                                                    \
         H5MM_xfree(X);                                                  \
         while(SLIST->curr_level>0 && SLIST->header->forward[SLIST->curr_level]==NULL) \
@@ -70,61 +77,69 @@
         SLIST->nobjs--;                                                 \
         HGOTO_DONE(tmp);
 
-/* Define the code template for searches for the "OP" in the H5SL_FIND macro */
-#define H5SL_FIND_SEARCH_FOUND(SLIST,X,UPDATE,I,ITEM)                   \
+/* Define the code template for searches for the "OP" in the H5SL_LOCATE macro */
+#define H5SL_LOCATE_SEARCH_FOUND(SLIST,X,UPDATE,I,ITEM)                 \
         HGOTO_DONE(X->item);
 
-/* Define a code template for updating the "update" vector for the "DOUPDATE" in the H5SL_FIND macro */
-#define H5SL_FIND_YES_UPDATE(X,UPDATE,I)                                \
+/* Define the code template for finds for the "OP" in the H5SL_LOCATE macro */
+#define H5SL_LOCATE_FIND_FOUND(SLIST,X,UPDATE,I,ITEM)                   \
+        HGOTO_DONE(X);
+
+/* Define a code template for updating the "update" vector for the "DOUPDATE" in the H5SL_LOCATE macro */
+#define H5SL_LOCATE_YES_UPDATE(X,UPDATE,I)                              \
         UPDATE[I]=&X->forward[I];
 
-/* Define a code template for _NOT_ updating the "update" vector for the "DOUPDATE" in the H5SL_FIND macro */
-#define H5SL_FIND_NO_UPDATE(X,UPDATE,I)
+/* Define a code template for _NOT_ updating the "update" vector for the "DOUPDATE" in the H5SL_LOCATE macro */
+#define H5SL_LOCATE_NO_UPDATE(X,UPDATE,I)
 
-/* Define a code template for comparing scalar keys for the "CMP" in the H5SL_FIND macro */
-#define H5SL_FIND_SCALAR_CMP(TYPE,PKEY1,PKEY2)                          \
+/* Define a code template for comparing scalar keys for the "CMP" in the H5SL_LOCATE macro */
+#define H5SL_LOCATE_SCALAR_CMP(TYPE,PKEY1,PKEY2)                        \
         (*(TYPE *)PKEY1<*(TYPE *)PKEY2)
 
-/* Define a code template for comparing string keys for the "CMP" in the H5SL_FIND macro */
-#define H5SL_FIND_STRING_CMP(TYPE,PKEY1,PKEY2)                          \
+/* Define a code template for comparing string keys for the "CMP" in the H5SL_LOCATE macro */
+#define H5SL_LOCATE_STRING_CMP(TYPE,PKEY1,PKEY2)                        \
         (HDstrcmp(PKEY1,PKEY2)<0)
 
-/* Define a code template for comparing scalar keys for the "EQ" in the H5SL_FIND macro */
-#define H5SL_FIND_SCALAR_EQ(TYPE,PKEY1,PKEY2)                           \
+/* Define a code template for comparing scalar keys for the "EQ" in the H5SL_LOCATE macro */
+#define H5SL_LOCATE_SCALAR_EQ(TYPE,PKEY1,PKEY2)                         \
         (*(TYPE *)PKEY1==*(TYPE *)PKEY2)
 
-/* Define a code template for comparing string keys for the "EQ" in the H5SL_FIND macro */
-#define H5SL_FIND_STRING_EQ(TYPE,PKEY1,PKEY2)                           \
+/* Define a code template for comparing string keys for the "EQ" in the H5SL_LOCATE macro */
+#define H5SL_LOCATE_STRING_EQ(TYPE,PKEY1,PKEY2)                         \
         (HDstrcmp(PKEY1,PKEY2)==0)
 
 /* Macro used to find node for operation */
-#define H5SL_FIND(OP,DOUPDATE,CMP,SLIST,X,UPDATE,I,TYPE,ITEM,KEY,CHECKED) \
+#define H5SL_LOCATE(OP,DOUPDATE,CMP,SLIST,X,UPDATE,I,TYPE,ITEM,KEY,CHECKED) \
     CHECKED=NULL;                                                       \
     for(I=(int)SLIST->curr_level; I>=0; I--) {                          \
         if(X->forward[I]!=CHECKED) {                                    \
-            while(X->forward[I] && H5_GLUE3(H5SL_FIND_,CMP,_CMP)(TYPE,X->forward[I]->key,KEY) ) \
+            while(X->forward[I] && H5_GLUE3(H5SL_LOCATE_,CMP,_CMP)(TYPE,X->forward[I]->key,KEY) ) \
                 X=X->forward[I];                                        \
             CHECKED=X->forward[I];                                      \
         } /* end if */                                                  \
-        H5_GLUE3(H5SL_FIND_,DOUPDATE,_UPDATE)(X,UPDATE,I)               \
+        H5_GLUE3(H5SL_LOCATE_,DOUPDATE,_UPDATE)(X,UPDATE,I)             \
     } /* end for */                                                     \
     X=X->forward[0];                                                    \
-    if(X!=NULL && H5_GLUE3(H5SL_FIND_,CMP,_EQ)(TYPE,X->key,KEY) ) {     \
+    if(X!=NULL && H5_GLUE3(H5SL_LOCATE_,CMP,_EQ)(TYPE,X->key,KEY) ) {   \
         /* What to do when a node is found */				\
-        H5_GLUE3(H5SL_FIND_,OP,_FOUND)(SLIST,X,UPDATE,I,ITEM)           \
+        H5_GLUE3(H5SL_LOCATE_,OP,_FOUND)(SLIST,X,UPDATE,I,ITEM)         \
     } /* end if */
 
 /* Macro used to insert node */
 #define H5SL_INSERT(CMP,SLIST,X,UPDATE,I,TYPE,ITEM,KEY,CHECKED)         \
-    H5SL_FIND(INSERT,YES,CMP,SLIST,X,UPDATE,I,TYPE,ITEM,KEY,CHECKED)
+    H5SL_LOCATE(INSERT,YES,CMP,SLIST,X,UPDATE,I,TYPE,ITEM,KEY,CHECKED)
 
 /* Macro used to remove node */
 #define H5SL_REMOVE(CMP,SLIST,X,UPDATE,I,TYPE,ITEM,KEY,CHECKED)         \
-    H5SL_FIND(REMOVE,YES,CMP,SLIST,X,UPDATE,I,TYPE,ITEM,KEY,CHECKED)
+    H5SL_LOCATE(REMOVE,YES,CMP,SLIST,X,UPDATE,I,TYPE,ITEM,KEY,CHECKED)
 
 /* Macro used to search for node */
 #define H5SL_SEARCH(CMP,SLIST,X,UPDATE,I,TYPE,ITEM,KEY,CHECKED)         \
-    H5SL_FIND(SEARCH,NO,CMP,SLIST,X,UPDATE,I,TYPE,ITEM,KEY,CHECKED)
+    H5SL_LOCATE(SEARCH,NO,CMP,SLIST,X,UPDATE,I,TYPE,ITEM,KEY,CHECKED)
+
+/* Macro used to find a node */
+#define H5SL_FIND(CMP,SLIST,X,UPDATE,I,TYPE,ITEM,KEY,CHECKED)           \
+    H5SL_LOCATE(FIND,NO,CMP,SLIST,X,UPDATE,I,TYPE,ITEM,KEY,CHECKED)
 
 
 /* Private typedefs & structs */
@@ -135,6 +150,7 @@ struct H5SL_node_t {
     void *item;                         /* Pointer to node's item */
     size_t level;                       /* The level of this node */
     struct H5SL_node_t **forward;       /* Array of forward pointers from this node */
+    struct H5SL_node_t *backward;       /* Backward pointer from this node */
 };
 
 /* Main skip list data structure */
@@ -149,11 +165,15 @@ struct H5SL_t {
     int curr_level;             /* Current top level used in list */
     size_t nobjs;               /* Number of active objects in skip list */
     H5SL_node_t *header;        /* Header for nodes in skip list */
+    H5SL_node_t *last;          /* Pointer to last node in skip list */
 };
 
 /* Static functions */
 static size_t H5SL_random_level(int p1, size_t max_level);
 static H5SL_node_t * H5SL_new_node(size_t lvl, void *item, const void *key);
+static H5SL_node_t *H5SL_insert_common(H5SL_t *slist, void *item, const void *key);
+static herr_t H5SL_release_common(H5SL_t *slist, H5SL_operator_t op, void *op_data);
+static herr_t H5SL_close_common(H5SL_t *slist, H5SL_operator_t op, void *op_data);
 
 /* Declare a free list to manage the H5SL_t struct */
 H5FL_DEFINE_STATIC(H5SL_t);
@@ -281,6 +301,234 @@ done:
 
 /*--------------------------------------------------------------------------
  NAME
+    H5SL_insert_common
+ PURPOSE
+    Common code for inserting an object into a skip list
+ USAGE
+    H5SL_node_t *H5SL_insert_common(slist,item,key)
+        H5SL_t *slist;          IN/OUT: Pointer to skip list
+        void *item;             IN: Item to insert
+        void *key;              IN: Key for item to insert
+
+ RETURNS
+    Returns pointer to new node on success, NULL on failure.
+ DESCRIPTION
+    Common code for inserting an element into a skip list.
+ GLOBAL VARIABLES
+ COMMENTS, BUGS, ASSUMPTIONS
+    Inserting an item with the same key as an existing object fails.
+ EXAMPLES
+ REVISION LOG
+--------------------------------------------------------------------------*/
+static H5SL_node_t *
+H5SL_insert_common(H5SL_t *slist, void *item, const void *key)
+{
+    H5SL_node_t **update[H5SL_LEVEL_MAX];       /* 'update' vector */
+    H5SL_node_t *checked;                       /* Pointer to last node checked */
+    H5SL_node_t *x;                             /* Current node to examine */
+    size_t lvl;                                 /* Level of new node */
+    int i;                                      /* Local index value */
+    H5SL_node_t *ret_value;                     /* Return value */
+
+    FUNC_ENTER_NOAPI_NOINIT(H5SL_insert_common);
+
+    /* Check args */
+    assert(slist);
+    assert(key);
+
+    /* Check internal consistency */
+    /* (Pre-condition) */
+
+    /* Insert item into skip list */
+
+    /* Work through the forward pointers for a node, finding the node at each
+     * level that is before the location to insert
+     */
+    x=slist->header;
+    switch(slist->type) {
+        case H5SL_TYPE_INT:
+            H5SL_INSERT(SCALAR,slist,x,update,i,const int,item,key,checked)
+            break;
+
+        case H5SL_TYPE_HADDR:
+            H5SL_INSERT(SCALAR,slist,x,update,i,const haddr_t,item,key,checked)
+            break;
+
+        case H5SL_TYPE_STR:
+            H5SL_INSERT(STRING,slist,x,update,i,char *,item,key,checked)
+            break;
+
+        case H5SL_TYPE_HSIZE:
+            H5SL_INSERT(SCALAR,slist,x,update,i,const hsize_t,item,key,checked)
+            break;
+
+        case H5SL_TYPE_UNSIGNED:
+            H5SL_INSERT(SCALAR,slist,x,update,i,const unsigned,item,key,checked)
+            break;
+    } /* end switch */
+
+    /* 'key' must not have been found in existing list, if we get here */
+
+    /* Generate level for new node */
+    lvl=H5SL_random_level(slist->p1,slist->max_level);
+    if((int)lvl>slist->curr_level) {
+        /* Cap the increase in the current level to just one greater */
+        lvl=slist->curr_level+1;
+
+        /* Set the update pointer correctly */
+        update[lvl]=&slist->header->forward[lvl];
+
+        /* Increase the maximum level of the list */
+        slist->curr_level=(int)lvl;
+    } /* end if */
+
+    /* Create new node of proper level */
+    if((x=H5SL_new_node(lvl,item,key))==NULL)
+        HGOTO_ERROR(H5E_SLIST,H5E_NOSPACE,NULL,"can't create new skip list node");
+
+    /* Update the backward links */
+    if(*update[0]!=NULL) {
+        x->backward=(*update[0])->backward;
+        (*update[0])->backward=x;
+    } /* end if */
+    else {
+        HDassert(slist->last);
+        x->backward=slist->last;
+        slist->last=x;
+    } /* end else */
+
+    /* Link the new node into the existing forward pointers */
+    for(i=0; i<=(int)lvl; i++) {
+        x->forward[i]=*update[i];
+        *update[i]=x;
+    } /* end for */
+
+    /* Increment the number of nodes in the skip list */
+    slist->nobjs++;
+
+    /* Set return value */
+    ret_value=x;
+
+done:
+    FUNC_LEAVE_NOAPI(ret_value);
+} /* end H5SL_insert_common() */
+
+
+/*--------------------------------------------------------------------------
+ NAME
+    H5SL_release_common
+ PURPOSE
+    Release all nodes from a skip list, optionally calling a 'free' operator
+ USAGE
+    herr_t H5SL_release_common(slist)
+        H5SL_t *slist;            IN/OUT: Pointer to skip list to release nodes
+        H5SL_operator_t op;     IN: Callback function to free item & key
+        void *op_data;          IN/OUT: Pointer to application data for callback
+
+ RETURNS
+    Returns non-negative on success, negative on failure.
+ DESCRIPTION
+    Release all the nodes in a skip list.  The 'op' routine is called for
+    each node in the list.
+ GLOBAL VARIABLES
+ COMMENTS, BUGS, ASSUMPTIONS
+    The return value from the 'op' routine is ignored.
+
+    The skip list itself is still valid, it just has all its nodes removed.
+ EXAMPLES
+ REVISION LOG
+--------------------------------------------------------------------------*/
+herr_t
+H5SL_release_common(H5SL_t *slist, H5SL_operator_t op, void *op_data)
+{
+    H5SL_node_t *node, *next_node;      /* Pointers to skip list nodes */
+    size_t u;                   /* Local index variable */
+
+    FUNC_ENTER_NOAPI_NOINIT_NOFUNC(H5SL_release_common);
+
+    /* Check args */
+    assert(slist);
+
+    /* Check internal consistency */
+    /* (Pre-condition) */
+
+    /* Free skip list nodes */
+    node=slist->header->forward[0];
+    while(node!=NULL) {
+        next_node=node->forward[0];
+
+        /* Call callback, if one is given */
+        if(op!=NULL)
+            (void)(op)(node->item,(void *)node->key,op_data);
+
+        H5MM_xfree(node);
+        node=next_node;
+    } /* end while */
+
+    /* Reset the header pointers */
+    for(u=0; u<slist->max_level; u++)
+        slist->header->forward[u]=NULL;
+
+    /* Reset the last pointer */
+    slist->last=slist->header;
+
+    /* Reset the dynamic internal fields */
+    slist->curr_level=-1;
+    slist->nobjs=0;
+
+    FUNC_LEAVE_NOAPI(SUCCEED);
+} /* end H5SL_release_common() */
+
+
+/*--------------------------------------------------------------------------
+ NAME
+    H5SL_close_common
+ PURPOSE
+    Close a skip list, deallocating it and potentially freeing all its nodes.
+ USAGE
+    herr_t H5SL_close_common(slist,op,opdata)
+        H5SL_t *slist;          IN/OUT: Pointer to skip list to close
+        H5SL_operator_t op;     IN: Callback function to free item & key
+        void *op_data;          IN/OUT: Pointer to application data for callback
+
+ RETURNS
+    Returns non-negative on success, negative on failure.
+ DESCRIPTION
+    Close a skip list, freeing all internal information.  Any objects left in
+    the skip list have the 'op' routine called for each.
+ GLOBAL VARIABLES
+ COMMENTS, BUGS, ASSUMPTIONS
+    If the 'op' routine returns non-zero, only the nodes up to that
+    point in the list are released and the list is still valid.
+ EXAMPLES
+ REVISION LOG
+--------------------------------------------------------------------------*/
+herr_t
+H5SL_close_common(H5SL_t *slist, H5SL_operator_t op, void *op_data)
+{
+    FUNC_ENTER_NOAPI_NOINIT_NOFUNC(H5SL_close_common);
+
+    /* Check args */
+    assert(slist);
+
+    /* Check internal consistency */
+    /* (Pre-condition) */
+
+    /* Free skip list nodes */
+    (void)H5SL_release_common(slist,op,op_data);      /* always succeeds */
+
+    /* Release header node */
+    H5MM_xfree(slist->header);
+
+    /* Free skip list object */
+    H5FL_FREE(H5SL_t,slist);
+
+    FUNC_LEAVE_NOAPI(SUCCEED);
+} /* end H5SL_close_common() */
+
+
+/*--------------------------------------------------------------------------
+ NAME
     H5SL_create
  PURPOSE
     Create a skip list
@@ -309,7 +557,7 @@ H5SL_create(H5SL_type_t type, double p, size_t max_level)
     /* Check args */
     HDassert(p>0.0 && p<1.0);
     HDassert(max_level>0 && max_level<=H5SL_LEVEL_MAX);
-    HDassert(type>=H5SL_TYPE_INT && type<=H5SL_TYPE_HSIZE);
+    HDassert(type>=H5SL_TYPE_INT && type<=H5SL_TYPE_UNSIGNED);
 
     /* Allocate skip list structure */
     if((new_slist=H5FL_MALLOC(H5SL_t))==NULL)
@@ -333,8 +581,12 @@ H5SL_create(H5SL_type_t type, double p, size_t max_level)
     for(u=0; u<max_level; u++)
         header->forward[u]=NULL;
 
+    /* Initialize header node's backward pointer */
+    header->backward=NULL;
+
     /* Attach the header */
     new_slist->header=header;
+    new_slist->last=header;
 
     /* Set the return value */
     ret_value=new_slist;
@@ -388,7 +640,7 @@ H5SL_count(H5SL_t *slist)
  NAME
     H5SL_insert
  PURPOSE
-    Insert an objects into a skip list
+    Insert an object into a skip list
  USAGE
     herr_t H5SL_insert(slist,item,key)
         H5SL_t *slist;          IN/OUT: Pointer to skip list
@@ -408,14 +660,102 @@ H5SL_count(H5SL_t *slist)
 herr_t
 H5SL_insert(H5SL_t *slist, void *item, const void *key)
 {
+    herr_t ret_value=SUCCEED;                   /* Return value */
+
+    FUNC_ENTER_NOAPI_NOINIT(H5SL_insert);
+
+    /* Check args */
+    assert(slist);
+    assert(key);
+
+    /* Check internal consistency */
+    /* (Pre-condition) */
+
+    /* Insert item into skip list */
+    if(H5SL_insert_common(slist,item,key)==NULL)
+        HGOTO_ERROR(H5E_SLIST,H5E_CANTINSERT,FAIL,"can't create new skip list node")
+
+done:
+    FUNC_LEAVE_NOAPI(ret_value);
+} /* end H5SL_insert() */
+
+
+/*--------------------------------------------------------------------------
+ NAME
+    H5SL_add
+ PURPOSE
+    Insert an object into a skip list
+ USAGE
+    H5SL_node_t *H5SL_add(slist,item,key)
+        H5SL_t *slist;          IN/OUT: Pointer to skip list
+        void *item;             IN: Item to insert
+        void *key;              IN: Key for item to insert
+
+ RETURNS
+    Returns pointer to new skip list node on success, NULL on failure.
+ DESCRIPTION
+    Insert element into a skip list and return the skip list node for the
+    new element in the list.
+ GLOBAL VARIABLES
+ COMMENTS, BUGS, ASSUMPTIONS
+    Inserting an item with the same key as an existing object fails.
+
+    This routine is a useful starting point for next/prev calls
+ EXAMPLES
+ REVISION LOG
+--------------------------------------------------------------------------*/
+H5SL_node_t *
+H5SL_add(H5SL_t *slist, void *item, const void *key)
+{
+    H5SL_node_t *ret_value;                   /* Return value */
+
+    FUNC_ENTER_NOAPI_NOINIT(H5SL_add);
+
+    /* Check args */
+    assert(slist);
+    assert(key);
+
+    /* Check internal consistency */
+    /* (Pre-condition) */
+
+    /* Insert item into skip list */
+    if((ret_value=H5SL_insert_common(slist,item,key))==NULL)
+        HGOTO_ERROR(H5E_SLIST,H5E_CANTINSERT,NULL,"can't create new skip list node")
+
+done:
+    FUNC_LEAVE_NOAPI(ret_value);
+} /* end H5SL_add() */
+
+
+/*--------------------------------------------------------------------------
+ NAME
+    H5SL_remove
+ PURPOSE
+    Removes an object from a skip list
+ USAGE
+    void *H5SL_remove(slist,key)
+        H5SL_t *slist;          IN/OUT: Pointer to skip list
+        void *key;              IN: Key for item to remove
+
+ RETURNS
+    Returns pointer to item removed on success, NULL on failure.
+ DESCRIPTION
+    Remove element from a skip list.
+ GLOBAL VARIABLES
+ COMMENTS, BUGS, ASSUMPTIONS
+ EXAMPLES
+ REVISION LOG
+--------------------------------------------------------------------------*/
+void *
+H5SL_remove(H5SL_t *slist, const void *key)
+{
     H5SL_node_t **update[H5SL_LEVEL_MAX];       /* 'update' vector */
     H5SL_node_t *checked;                       /* Pointer to last node checked */
     H5SL_node_t *x;                             /* Current node to examine */
-    size_t lvl;                                 /* Level of new node */
     int i;                                      /* Local index value */
-    herr_t ret_value=SUCCEED;                   /* Return value */
+    void *ret_value=NULL;                       /* Return value */
 
-    FUNC_ENTER_NOAPI_NOINIT(H5SL_insert);
+    FUNC_ENTER_NOAPI_NOINIT_NOFUNC(H5SL_remove);
 
     /* Check args */
     assert(slist);
@@ -424,68 +764,44 @@ H5SL_insert(H5SL_t *slist, void *item, const void *key)
     /* Check internal consistency */
     /* (Pre-condition) */
 
-    /* Insert item into skip list */
+    /* Remove item from skip list */
 
     /* Work through the forward pointers for a node, finding the node at each
-     * level that is before the location to insert
+     * level that is before the location to remove
      */
     x=slist->header;
     switch(slist->type) {
         case H5SL_TYPE_INT:
-            H5SL_INSERT(SCALAR,slist,x,update,i,const int,item,key,checked)
+            H5SL_REMOVE(SCALAR,slist,x,update,i,const int,-,key,checked)
             break;
 
         case H5SL_TYPE_HADDR:
-            H5SL_INSERT(SCALAR,slist,x,update,i,const haddr_t,item,key,checked)
+            H5SL_REMOVE(SCALAR,slist,x,update,i,const haddr_t,-,key,checked)
             break;
 
         case H5SL_TYPE_STR:
-            H5SL_INSERT(STRING,slist,x,update,i,char *,item,key,checked)
+            H5SL_REMOVE(STRING,slist,x,update,i,char *,-,key,checked)
             break;
 
         case H5SL_TYPE_HSIZE:
-            H5SL_INSERT(SCALAR,slist,x,update,i,const hsize_t,item,key,checked)
+            H5SL_REMOVE(SCALAR,slist,x,update,i,const hsize_t,-,key,checked)
             break;
-    } /* end switch */
-
-    /* 'key' must not have been found in existing list, if we get here */
 
-    /* Generate level for new node */
-    lvl=H5SL_random_level(slist->p1,slist->max_level);
-    if((int)lvl>slist->curr_level) {
-        /* Cap the increase in the current level to just one greater */
-        lvl=slist->curr_level+1;
-
-        /* Set the update pointer correctly */
-        update[lvl]=&slist->header->forward[lvl];
-
-        /* Increase the maximum level of the list */
-        slist->curr_level=(int)lvl;
-    } /* end if */
-
-    /* Create new node of proper level */
-    if((x=H5SL_new_node(lvl,item,key))==NULL)
-        HGOTO_ERROR(H5E_SLIST,H5E_NOSPACE,FAIL,"can't create new skip list node");
-
-    /* Link the new node into the existing list */
-    for(i=0; i<=(int)lvl; i++) {
-        x->forward[i]=*update[i];
-        *update[i]=x;
-    } /* end for */
-
-    /* Increment the number of nodes in the skip list */
-    slist->nobjs++;
+        case H5SL_TYPE_UNSIGNED:
+            H5SL_REMOVE(SCALAR,slist,x,update,i,const unsigned,-,key,checked)
+            break;
+    } /* end switch */
 
 done:
     FUNC_LEAVE_NOAPI(ret_value);
-} /* end H5SL_insert() */
+} /* end H5SL_remove() */
 
 
 /*--------------------------------------------------------------------------
  NAME
     H5SL_search
  PURPOSE
-    Search for objects into a skip list
+    Search for object in a skip list
  USAGE
     void *H5SL_search(slist,key)
         H5SL_t *slist;          IN/OUT: Pointer to skip list
@@ -539,9 +855,13 @@ H5SL_search(H5SL_t *slist, const void *key)
         case H5SL_TYPE_HSIZE:
             H5SL_SEARCH(SCALAR,slist,x,-,i,const hsize_t,-,key,checked)
             break;
+
+        case H5SL_TYPE_UNSIGNED:
+            H5SL_SEARCH(SCALAR,slist,x,-,i,const unsigned,-,key,checked)
+            break;
     } /* end switch */
 
-    /* 'key' must not have been found in existing list, if we get here */
+    /* 'key' must not have been found in list, if we get here */
     ret_value=NULL;
 
 done:
@@ -551,33 +871,35 @@ done:
 
 /*--------------------------------------------------------------------------
  NAME
-    H5SL_remove
+    H5SL_less
  PURPOSE
-    Removes an object from a skip list
+    Search for object in a skip list that is less than or equal to 'key'
  USAGE
-    void *H5SL_remove(slist,key)
+    void *H5SL_less(slist,key)
         H5SL_t *slist;          IN/OUT: Pointer to skip list
-        void *key;              IN: Key for item to remove
+        void *key;              IN: Key for item to search for
 
  RETURNS
-    Returns pointer to item removed on success, NULL on failure.
+    Returns pointer to item who key is less than or equal to 'key' on success,
+        NULL on failure
  DESCRIPTION
-    Remove element from a skip list.
+    Search for an object in a skip list, according to it's key, returning the
+    object itself (for an exact match), or the object with the next highest
+    key that is less than 'key'
  GLOBAL VARIABLES
  COMMENTS, BUGS, ASSUMPTIONS
  EXAMPLES
  REVISION LOG
 --------------------------------------------------------------------------*/
 void *
-H5SL_remove(H5SL_t *slist, const void *key)
+H5SL_less(H5SL_t *slist, const void *key)
 {
-    H5SL_node_t **update[H5SL_LEVEL_MAX];       /* 'update' vector */
     H5SL_node_t *checked;                       /* Pointer to last node checked */
     H5SL_node_t *x;                             /* Current node to examine */
     int i;                                      /* Local index value */
-    void *ret_value=NULL;                       /* Return value */
+    void *ret_value;                            /* Return value */
 
-    FUNC_ENTER_NOAPI_NOINIT_NOFUNC(H5SL_remove);
+    FUNC_ENTER_NOAPI_NOINIT_NOFUNC(H5SL_less);
 
     /* Check args */
     assert(slist);
@@ -586,33 +908,127 @@ H5SL_remove(H5SL_t *slist, const void *key)
     /* Check internal consistency */
     /* (Pre-condition) */
 
-    /* Remove item from skip list */
+    /* Insert item into skip list */
 
     /* Work through the forward pointers for a node, finding the node at each
-     * level that is before the location to remove
+     * level that is before the location to insert
      */
     x=slist->header;
     switch(slist->type) {
         case H5SL_TYPE_INT:
-            H5SL_REMOVE(SCALAR,slist,x,update,i,const int,-,key,checked)
+            H5SL_SEARCH(SCALAR,slist,x,-,i,const int,-,key,checked)
             break;
 
         case H5SL_TYPE_HADDR:
-            H5SL_REMOVE(SCALAR,slist,x,update,i,const haddr_t,-,key,checked)
+            H5SL_SEARCH(SCALAR,slist,x,-,i,const haddr_t,-,key,checked)
             break;
 
         case H5SL_TYPE_STR:
-            H5SL_REMOVE(STRING,slist,x,update,i,char *,-,key,checked)
+            H5SL_SEARCH(STRING,slist,x,-,i,char *,-,key,checked)
             break;
 
         case H5SL_TYPE_HSIZE:
-            H5SL_REMOVE(SCALAR,slist,x,update,i,const hsize_t,-,key,checked)
+            H5SL_SEARCH(SCALAR,slist,x,-,i,const hsize_t,-,key,checked)
+            break;
+
+        case H5SL_TYPE_UNSIGNED:
+            H5SL_SEARCH(SCALAR,slist,x,-,i,const unsigned,-,key,checked)
             break;
     } /* end switch */
 
+    /* An exact match for 'key' must not have been found in list, if we get here */
+    /* Check for a node with a key that is less than the given 'key' */
+    if(x==NULL) {
+        /* Check for walking off the list */
+        if(slist->last!=slist->header)
+            ret_value=slist->last->item;
+        else
+            ret_value=NULL;
+    } /* end if */
+    else {
+        if(x->backward!=slist->header)
+            ret_value=x->backward->item;
+        else
+            ret_value=NULL;
+    } /* end else */
+
 done:
     FUNC_LEAVE_NOAPI(ret_value);
-} /* end H5SL_remove() */
+} /* end H5SL_less() */
+
+
+/*--------------------------------------------------------------------------
+ NAME
+    H5SL_find
+ PURPOSE
+    Search for _node_ in a skip list
+ USAGE
+    H5SL_node_t *H5SL_node(slist,key)
+        H5SL_t *slist;          IN/OUT: Pointer to skip list
+        void *key;              IN: Key for item to search for
+
+ RETURNS
+    Returns pointer to _node_ matching key on success, NULL on failure
+ DESCRIPTION
+    Search for an object in a skip list, according to it's key and returns
+    the node that the object is attached to
+ GLOBAL VARIABLES
+ COMMENTS, BUGS, ASSUMPTIONS
+    This routine is a useful starting point for next/prev calls
+ EXAMPLES
+ REVISION LOG
+--------------------------------------------------------------------------*/
+H5SL_node_t *
+H5SL_find(H5SL_t *slist, const void *key)
+{
+    H5SL_node_t *checked;                       /* Pointer to last node checked */
+    H5SL_node_t *x;                             /* Current node to examine */
+    int i;                                      /* Local index value */
+    H5SL_node_t *ret_value;                     /* Return value */
+
+    FUNC_ENTER_NOAPI_NOINIT_NOFUNC(H5SL_find);
+
+    /* Check args */
+    assert(slist);
+    assert(key);
+
+    /* Check internal consistency */
+    /* (Pre-condition) */
+
+    /* Insert item into skip list */
+
+    /* Work through the forward pointers for a node, finding the node at each
+     * level that is before the location to insert
+     */
+    x=slist->header;
+    switch(slist->type) {
+        case H5SL_TYPE_INT:
+            H5SL_FIND(SCALAR,slist,x,-,i,const int,-,key,checked)
+            break;
+
+        case H5SL_TYPE_HADDR:
+            H5SL_FIND(SCALAR,slist,x,-,i,const haddr_t,-,key,checked)
+            break;
+
+        case H5SL_TYPE_STR:
+            H5SL_FIND(STRING,slist,x,-,i,char *,-,key,checked)
+            break;
+
+        case H5SL_TYPE_HSIZE:
+            H5SL_FIND(SCALAR,slist,x,-,i,const hsize_t,-,key,checked)
+            break;
+
+        case H5SL_TYPE_UNSIGNED:
+            H5SL_FIND(SCALAR,slist,x,-,i,const unsigned,-,key,checked)
+            break;
+    } /* end switch */
+
+    /* 'key' must not have been found in list, if we get here */
+    ret_value=NULL;
+
+done:
+    FUNC_LEAVE_NOAPI(ret_value);
+} /* end H5SL_find() */
 
 
 /*--------------------------------------------------------------------------
@@ -685,6 +1101,76 @@ H5SL_next(H5SL_node_t *slist_node)
 
 /*--------------------------------------------------------------------------
  NAME
+    H5SL_prev
+ PURPOSE
+    Gets a pointer to the previos node in a skip list
+ USAGE
+    H5SL_node_t *H5SL_prev(slist_node)
+        H5SL_node_t *slist_node;          IN: Pointer to skip list node
+
+ RETURNS
+    Returns pointer to node before slist_node in skip list on success, NULL on failure.
+ DESCRIPTION
+    Retrieves a pointer to the previous node in a skip list, for iterating over
+    the list.
+ GLOBAL VARIABLES
+ COMMENTS, BUGS, ASSUMPTIONS
+ EXAMPLES
+ REVISION LOG
+--------------------------------------------------------------------------*/
+H5SL_node_t *
+H5SL_prev(H5SL_node_t *slist_node)
+{
+    FUNC_ENTER_NOAPI_NOINIT_NOFUNC(H5SL_prev);
+
+    /* Check args */
+    assert(slist_node);
+
+    /* Check internal consistency */
+    /* (Pre-condition) */
+
+    /* Walk backward, detecting the header node (which has it's key set to NULL) */
+    FUNC_LEAVE_NOAPI(slist_node->backward->key==NULL ? NULL : slist_node->backward);
+} /* end H5SL_prev() */
+
+
+/*--------------------------------------------------------------------------
+ NAME
+    H5SL_last
+ PURPOSE
+    Gets a pointer to the lsat node in a skip list
+ USAGE
+    H5SL_node_t *H5SL_last(slist)
+        H5SL_t *slist;          IN: Pointer to skip list
+
+ RETURNS
+    Returns pointer to last node in skip list on success, NULL on failure.
+ DESCRIPTION
+    Retrieves a pointer to the last node in a skip list, for iterating over
+    the list.
+ GLOBAL VARIABLES
+ COMMENTS, BUGS, ASSUMPTIONS
+ EXAMPLES
+ REVISION LOG
+--------------------------------------------------------------------------*/
+H5SL_node_t *
+H5SL_last(H5SL_t *slist)
+{
+    FUNC_ENTER_NOAPI_NOINIT_NOFUNC(H5SL_last);
+
+    /* Check args */
+    assert(slist);
+
+    /* Check internal consistency */
+    /* (Pre-condition) */
+
+    /* Find last node, avoiding the header node */
+    FUNC_LEAVE_NOAPI(slist->last==slist->header ? NULL : slist->last);
+} /* end H5SL_last() */
+
+
+/*--------------------------------------------------------------------------
+ NAME
     H5SL_item
  PURPOSE
     Gets pointer to the 'item' for a skip list node
@@ -794,15 +1280,13 @@ H5SL_iterate(H5SL_t *slist, H5SL_operator_t op, void *op_data)
     nodes are not deallocated.
  GLOBAL VARIABLES
  COMMENTS, BUGS, ASSUMPTIONS
+    The skip list itself is still valid, it just has all its nodes removed.
  EXAMPLES
  REVISION LOG
 --------------------------------------------------------------------------*/
 herr_t
 H5SL_release(H5SL_t *slist)
 {
-    H5SL_node_t *node, *next_node;      /* Pointers to skip list nodes */
-    size_t u;                   /* Local index variable */
-
     FUNC_ENTER_NOAPI_NOINIT_NOFUNC(H5SL_release);
 
     /* Check args */
@@ -812,23 +1296,102 @@ H5SL_release(H5SL_t *slist)
     /* (Pre-condition) */
 
     /* Free skip list nodes */
-    node=slist->header->forward[0];
-    while(node!=NULL) {
-        next_node=node->forward[0];
-        H5MM_xfree(node);
-        node=next_node;
-    } /* end while */
+    H5SL_release_common(slist,NULL,NULL); /* always succeeds */
 
-    /* Reset the header pointers */
-    for(u=0; u<slist->max_level; u++)
-        slist->header->forward[u]=NULL;
+    FUNC_LEAVE_NOAPI(SUCCEED);
+} /* end H5SL_release() */
 
-    /* Reset the dynamic internal fields */
-    slist->curr_level=-1;
-    slist->nobjs=0;
+
+/*--------------------------------------------------------------------------
+ NAME
+    H5SL_free
+ PURPOSE
+    Release all nodes from a skip list, freeing all nodes
+ USAGE
+    herr_t H5SL_free(slist,op,op_data)
+        H5SL_t *slist;          IN/OUT: Pointer to skip list to release nodes
+        H5SL_operator_t op;     IN: Callback function to free item & key
+        void *op_data;          IN/OUT: Pointer to application data for callback
+
+ RETURNS
+    Returns non-negative on success, negative on failure.
+ DESCRIPTION
+    Release all the nodes in a skip list.  Any objects left in
+    the skip list have the 'op' routine called for each.
+ GLOBAL VARIABLES
+ COMMENTS, BUGS, ASSUMPTIONS
+    The skip list itself is still valid, it just has all its nodes removed.
+
+    The return value from the 'op' routine is ignored.
+
+    This routine is essentially a combination of iterating over all the nodes
+    (where the iterator callback is supposed to free the items and/or keys)
+    followed by a call to H5SL_release().
+ EXAMPLES
+ REVISION LOG
+--------------------------------------------------------------------------*/
+herr_t
+H5SL_free(H5SL_t *slist, H5SL_operator_t op, void *op_data)
+{
+    FUNC_ENTER_NOAPI_NOINIT_NOFUNC(H5SL_free);
+
+    /* Check args */
+    assert(slist);
+
+    /* Check internal consistency */
+    /* (Pre-condition) */
+
+    /* Free skip list nodes */
+    H5SL_release_common(slist,op,op_data); /* always succeeds */
 
     FUNC_LEAVE_NOAPI(SUCCEED);
-} /* end H5SL_release() */
+} /* end H5SL_free() */
+
+
+/*--------------------------------------------------------------------------
+ NAME
+    H5SL_destroy
+ PURPOSE
+    Close a skip list, deallocating it and freeing all its nodes.
+ USAGE
+    herr_t H5SL_destroy(slist,op,opdata)
+        H5SL_t *slist;          IN/OUT: Pointer to skip list to close
+        H5SL_operator_t op;     IN: Callback function to free item & key
+        void *op_data;          IN/OUT: Pointer to application data for callback
+
+ RETURNS
+    Returns non-negative on success, negative on failure.
+ DESCRIPTION
+    Close a skip list, freeing all internal information.  Any objects left in
+    the skip list have the 'op' routine called for each.
+ GLOBAL VARIABLES
+ COMMENTS, BUGS, ASSUMPTIONS
+    The return value from the 'op' routine is ignored.
+
+    This routine is essentially a combination of iterating over all the nodes
+    (where the iterator callback is supposed to free the items and/or keys)
+    followed by a call to H5SL_close().
+ EXAMPLES
+ REVISION LOG
+--------------------------------------------------------------------------*/
+herr_t
+H5SL_destroy(H5SL_t *slist, H5SL_operator_t op, void *op_data)
+{
+    herr_t ret_value=SUCCEED;   /* Return value */
+
+    FUNC_ENTER_NOAPI_NOINIT_NOFUNC(H5SL_destroy);
+
+    /* Check args */
+    assert(slist);
+
+    /* Check internal consistency */
+    /* (Pre-condition) */
+
+    /* Close skip list */
+    (void)H5SL_close_common(slist,op,op_data); /* always succeeds */
+
+    FUNC_LEAVE_NOAPI(ret_value);
+} /* end H5SL_destroy() */
 
 
 /*--------------------------------------------------------------------------
@@ -861,14 +1424,8 @@ H5SL_close(H5SL_t *slist)
     /* Check internal consistency */
     /* (Pre-condition) */
 
-    /* Free skip list nodes */
-    H5SL_release(slist);        /* always succeeds */
-
-    /* Release header node */
-    H5MM_xfree(slist->header);
-
-    /* Free skip list object */
-    H5FL_FREE(H5SL_t,slist);
+    /* Close skip list */
+    (void)H5SL_close_common(slist,NULL,NULL); /* always succeeds */
 
     FUNC_LEAVE_NOAPI(SUCCEED);
 } /* end H5SL_close() */