path: root/src/H5SL.c

/* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
 * Copyright by The HDF Group.                                               *
 * 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://hdfgroup.org/HDF5/doc/Copyright.html.  If you do not have          *
 * access to either file, you may request a copy from help@hdfgroup.org.     *
 * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * */

/*
 * Purpose:	Provides a skip list abstract data type.
 *
 *              (See "Skip Lists: A Probabilistic Alternative to Balanced Trees"
 *               by William Pugh for additional information)
 *
 *              (This implementation has the optimization for reducing key
 *               key comparisons mentioned in section 3.5 of "A Skip List
 *               Cookbook" by William Pugh)
 *
 *              (Also, this implementation has a couple of home-grown
 *               optimizations, including setting the "update" vector to the
 *               actual 'forward' pointer to update, instead of the node
 *               containing the forward pointer -QAK)
 *
 *              (Note: This implementation does not have the information for
 *               implementing the "Linear List Operations" (like insert/delete/
 *               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)
 *
 *              (We should also look into "Deterministic Skip Lists" (see
 *              paper by Munro, Papadakis & Sedgewick))
 *
 *              (There's also an article on "Alternating Skip Lists", which
 *              are similar to deterministic skip lists, in the August 2000
 *              issue of Dr. Dobb's Journal)
 *
 */

/* Interface initialization */
#define H5_INTERFACE_INIT_FUNC	H5SL_init_interface


/* Private headers needed */
#include "H5private.h"		/* Generic Functions			*/
#include "H5Eprivate.h"		/* Error handling		  	*/
#include "H5FLprivate.h"	/* Free Lists                           */
#include "H5SLprivate.h"	/* Skip list routines			*/

/* Local Macros */

/* Define the code template for insertions for the "OP" in the H5SL_LOCATE macro */
#define H5SL_LOCATE_INSERT_FOUND(SLIST,X,UPDATE,I)                      \
        HGOTO_ERROR(H5E_SLIST,H5E_CANTINSERT,NULL,"can't insert duplicate key");

/* Define the code template for removals for the "OP" in the H5SL_LOCATE macro */
/* (NOTE: the code in H5SL_remove_first() is largely the same, fix bugs in both places) */
#define H5SL_LOCATE_REMOVE_FOUND(SLIST,X,UPDATE,I)                      \
        void *tmp;                                                      \
                                                                        \
        for(I=0; I<=(int)SLIST->curr_level; I++) {                      \
            if(*UPDATE[I]!=X)                                           \
                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;                                                    \
        H5FL_ARR_FREE(H5SL_node_ptr_t,X);                               \
        while(SLIST->curr_level>0 && SLIST->header->forward[SLIST->curr_level]==NULL) \
            SLIST->curr_level--;                                        \
        SLIST->nobjs--;                                                 \
        HGOTO_DONE(tmp);

/* Define the code template for searches for the "OP" in the H5SL_LOCATE macro */
#define H5SL_LOCATE_SEARCH_FOUND(SLIST,X,UPDATE,I)                      \
        HGOTO_DONE(X->item);

/* Define the code template for finds for the "OP" in the H5SL_LOCATE macro */
#define H5SL_LOCATE_FIND_FOUND(SLIST,X,UPDATE,I)                        \
        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_LOCATE macro */
#define H5SL_LOCATE_NO_UPDATE(X,UPDATE,I)

/* 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_LOCATE macro */
#define H5SL_LOCATE_STRING_CMP(TYPE,PKEY1,PKEY2)                        \
        (HDstrcmp(PKEY1, PKEY2) < 0)

/* Define a code template for comparing H5_obj_t keys for the "CMP" in the H5SL_LOCATE macro */
#define H5SL_LOCATE_OBJ_CMP(TYPE,PKEY1,PKEY2)                           \
        ((((TYPE *)PKEY1)->fileno < ((TYPE *)PKEY2)->fileno) ? TRUE : (((TYPE *)PKEY1)->addr < ((TYPE *)PKEY2)->addr))

/* 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_LOCATE macro */
#define H5SL_LOCATE_STRING_EQ(TYPE,PKEY1,PKEY2)                         \
        (HDstrcmp(PKEY1, PKEY2) == 0)

/* Define a code template for comparing H5_obj_ keys for the "EQ" in the H5SL_LOCATE macro */
#define H5SL_LOCATE_OBJ_EQ(TYPE,PKEY1,PKEY2)                            \
        ((((TYPE *)PKEY1)->fileno == ((TYPE *)PKEY2)->fileno) && (((TYPE *)PKEY1)->addr == ((TYPE *)PKEY2)->addr))

/* Macro used to find node for operation */
#define H5SL_LOCATE(OP,DOUPDATE,CMP,SLIST,X,UPDATE,I,TYPE,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_LOCATE_,CMP,_CMP)(TYPE,X->forward[I]->key,KEY) ) \
                X=X->forward[I];                                        \
            CHECKED=X->forward[I];                                      \
        } /* end if */                                                  \
        H5_GLUE3(H5SL_LOCATE_,DOUPDATE,_UPDATE)(X,UPDATE,I)             \
    } /* end for */                                                     \
    X=X->forward[0];                                                    \
    if(X!=NULL && H5_GLUE3(H5SL_LOCATE_,CMP,_EQ)(TYPE,X->key,KEY) ) {   \
        /* What to do when a node is found */				\
        H5_GLUE3(H5SL_LOCATE_,OP,_FOUND)(SLIST,X,UPDATE,I)              \
    } /* end if */

/* Macro used to insert node */
#define H5SL_INSERT(CMP, SLIST, X, UPDATE, I, TYPE, KEY, CHECKED)       \
    H5SL_LOCATE(INSERT, YES, CMP, SLIST, X, UPDATE, I, TYPE, KEY, CHECKED)

/* Macro used to remove node */
#define H5SL_REMOVE(CMP, SLIST, X, UPDATE, I, TYPE, KEY, CHECKED)       \
    H5SL_LOCATE(REMOVE, YES, CMP, SLIST, X, UPDATE, I, TYPE, KEY, CHECKED)

/* Macro used to search for node */
#define H5SL_SEARCH(CMP, SLIST, X, UPDATE, I, TYPE, KEY, CHECKED)       \
    H5SL_LOCATE(SEARCH, NO, CMP, SLIST, X, UPDATE, I, TYPE, KEY, CHECKED)

/* Macro used to find a node */
#define H5SL_FIND(CMP, SLIST, X, UPDATE, I, TYPE, KEY, CHECKED)         \
    H5SL_LOCATE(FIND, NO, CMP, SLIST, X, UPDATE, I, TYPE, KEY, CHECKED)


/* Private typedefs & structs */

/* Skip list node data structure */
struct H5SL_node_t {
    const void *key;                    /* Pointer to node's key */
    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 */
struct H5SL_t {
    /* Static values for each list */
    H5SL_type_t type;   /* Type of skip list */
    double p;           /* Probability of using a higher level [0..1) */
    int p1;             /* Probability converted into appropriate value for random # generator on this machine */
    size_t max_level;   /* Maximum number of levels */

    /* Dynamic values for each list */
    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);

/* Declare a "base + array" list to manage the H5SL_node_t struct */
typedef H5SL_node_t *H5SL_node_ptr_t;
H5FL_BARR_DEFINE_STATIC(H5SL_node_t,H5SL_node_ptr_t,H5SL_LEVEL_MAX);


/*--------------------------------------------------------------------------
 NAME
    H5SL_init_interface
 PURPOSE
    Initialize interface-specific information
 USAGE
    herr_t H5SL_init_interface()

 RETURNS
    Non-negative on success/Negative on failure
 DESCRIPTION
    Initializes any interface-specific data or routines.
 GLOBAL VARIABLES
 COMMENTS, BUGS, ASSUMPTIONS
 EXAMPLES
 REVISION LOG
--------------------------------------------------------------------------*/
static herr_t
H5SL_init_interface(void)
{
    time_t curr_time;   /* Current time, for seeding random number generator */

    FUNC_ENTER_NOAPI_NOINIT_NOFUNC(H5SL_init_interface)

    /* Create randomized set of numbers */
    curr_time=HDtime(NULL);
    HDsrand((unsigned)curr_time);

    FUNC_LEAVE_NOAPI(SUCCEED)
} /* end H5SL_init_interface() */


/*--------------------------------------------------------------------------
 NAME
    H5SL_random_level
 PURPOSE
    Generate a random level
 USAGE
    size_t H5SL_random_level(p,max_level)
        int p1;                 IN: probability distribution
        size_t max_level;       IN: Maximum level for node height

 RETURNS
    Returns non-negative level value
 DESCRIPTION
    Count elements in a skip list.
 GLOBAL VARIABLES
 COMMENTS, BUGS, ASSUMPTIONS
    Do we really need a 'random' value, or is a series of nodes with the
    correct heights "good enough".  We could track the state of the nodes
    allocated for this list and issue node heights appropriately (i.e. 1,2,
    1,4,1,2,1,8,...) (or would that be 1,1,2,1,1,2,4,... ?)
 EXAMPLES
 REVISION LOG
--------------------------------------------------------------------------*/
static size_t
H5SL_random_level(int p1, size_t max_level)
{
    size_t lvl;         /* Level generated */

    FUNC_ENTER_NOAPI_NOINIT_NOFUNC(H5SL_random_level);

    /* Account for starting at zero offset */
    max_level--;

    lvl=0;
    while(HDrand()<p1 && lvl < max_level)
        lvl++;

    FUNC_LEAVE_NOAPI(lvl);
} /* end H5SL_random_level() */


/*--------------------------------------------------------------------------
 NAME
    H5SL_new_node
 PURPOSE
    Create a new skip list node
 USAGE
    H5SL_node_t *H5SL_new_node(lvl,item,key)
        size_t lvl;             IN: Level for node height
        void *item;             IN: Pointer to item info for node
        void *key;              IN: Pointer to key info for node

 RETURNS
    Returns a pointer to a skip list node on success, NULL on failure.
 DESCRIPTION
    Create a new skip list node of the specified height, setting the item
    and key values internally.
 GLOBAL VARIABLES
 COMMENTS, BUGS, ASSUMPTIONS
    This routine does _not_ initialize the 'forward' pointers

    We should set up a custom free-list for allocating & freeing these sort
    of nodes.
 EXAMPLES
 REVISION LOG
--------------------------------------------------------------------------*/
static H5SL_node_t *
H5SL_new_node(size_t lvl, void *item, const void *key)
{
    H5SL_node_t *ret_value;      /* New skip list node */

    FUNC_ENTER_NOAPI_NOINIT(H5SL_new_node);

    /* Allocate the node */
    if((ret_value=H5FL_ARR_MALLOC(H5SL_node_ptr_t,(lvl+1)))==NULL)
        HGOTO_ERROR(H5E_SLIST,H5E_NOSPACE,NULL,"memory allocation failed");

    /* Initialize node */
    ret_value->key=key;
    ret_value->item=item;
    ret_value->level=lvl;
    ret_value->forward=(H5SL_node_t **)((unsigned char *)ret_value+sizeof(H5SL_node_t));

done:
    FUNC_LEAVE_NOAPI(ret_value);
} /* end H5SL_new_node() */


/*--------------------------------------------------------------------------
 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, key, checked)
            break;

        case H5SL_TYPE_HADDR:
            H5SL_INSERT(SCALAR, slist, x, update, i, const haddr_t, key, checked)
            break;

        case H5SL_TYPE_STR:
            H5SL_INSERT(STRING, slist, x, update, i, char *, key, checked)
            break;

        case H5SL_TYPE_HSIZE:
            H5SL_INSERT(SCALAR, slist, x, update, i, const hsize_t, key, checked)
            break;

        case H5SL_TYPE_UNSIGNED:
            H5SL_INSERT(SCALAR, slist, x, update, i, const unsigned, key, checked)
            break;

        case H5SL_TYPE_SIZE:
            H5SL_INSERT(SCALAR, slist, x, update, i, const size_t, key, checked)
            break;

        case H5SL_TYPE_OBJ:
            H5SL_INSERT(OBJ, slist, x, update, i, const H5_obj_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,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)
            /* Casting away const OK -QAK */
            (void)(op)(node->item,(void *)node->key,op_data);

        H5FL_ARR_FREE(H5SL_node_ptr_t,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 */
    H5FL_ARR_FREE(H5SL_node_ptr_t,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
 USAGE
    H5SL_t *H5SL_create(void)

 RETURNS
    Returns a pointer to a skip list on success, NULL on failure.
 DESCRIPTION
    Create a skip list.
 GLOBAL VARIABLES
 COMMENTS, BUGS, ASSUMPTIONS
 EXAMPLES
 REVISION LOG
--------------------------------------------------------------------------*/
H5SL_t *
H5SL_create(H5SL_type_t type, double p, size_t max_level)
{
    H5SL_t *new_slist=NULL;     /* Pointer to new skip list object created */
    H5SL_node_t *header;        /* Pointer to skip list header node */
    size_t u;                   /* Local index variable */
    H5SL_t *ret_value;          /* Return value */

    FUNC_ENTER_NOAPI(H5SL_create,NULL);

    /* 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_OBJ);

    /* Allocate skip list structure */
    if((new_slist=H5FL_MALLOC(H5SL_t))==NULL)
        HGOTO_ERROR(H5E_SLIST,H5E_NOSPACE,NULL,"memory allocation failed");

    /* Set the static internal fields */
    new_slist->type=type;
    new_slist->p=p;
    new_slist->p1=(int)(p*RAND_MAX);
    new_slist->max_level=max_level;

    /* Set the dynamic internal fields */
    new_slist->curr_level=-1;
    new_slist->nobjs=0;

    /* Allocate the header node */
    if((header=H5SL_new_node(max_level-1,NULL,NULL))==NULL)
        HGOTO_ERROR(H5E_SLIST,H5E_NOSPACE,NULL,"memory allocation failed");

    /* Initialize header node's forward pointers */
    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;

done:
    /* Error cleanup */
    if(ret_value==NULL) {
        if(new_slist!=NULL) {
            H5FL_FREE(H5SL_t,new_slist);
        } /* end if */
    } /* end if */

    FUNC_LEAVE_NOAPI(ret_value);
} /* end H5SL_create() */


/*--------------------------------------------------------------------------
 NAME
    H5SL_count
 PURPOSE
    Count the number of objects in a skip list
 USAGE
    size_t H5SL_count(slist)
        H5SL_t *slist;            IN: Pointer to skip list to count

 RETURNS
    Returns number of objects on success, can't fail
 DESCRIPTION
    Count elements in a skip list.
 GLOBAL VARIABLES
 COMMENTS, BUGS, ASSUMPTIONS
 EXAMPLES
 REVISION LOG
--------------------------------------------------------------------------*/
size_t
H5SL_count(H5SL_t *slist)
{
    FUNC_ENTER_NOAPI_NOINIT_NOFUNC(H5SL_count);

    /* Check args */
    assert(slist);

    /* Check internal consistency */
    /* (Pre-condition) */

    FUNC_LEAVE_NOAPI(slist->nobjs);
} /* end H5SL_count() */


/*--------------------------------------------------------------------------
 NAME
    H5SL_insert
 PURPOSE
    Insert an object into a skip list
 USAGE
    herr_t H5SL_insert(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 non-negative on success, negative on failure.
 DESCRIPTION
    Insert 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
--------------------------------------------------------------------------*/
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 */
    int i;                                      /* Local index value */
    void *ret_value=NULL;                       /* Return value */

    FUNC_ENTER_NOAPI_NOINIT_NOFUNC(H5SL_remove);

    /* Check args */
    assert(slist);
    assert(key);

    /* Check internal consistency */
    /* (Pre-condition) */

    /* 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 remove
     */
    x=slist->header;
    switch(slist->type) {
        case H5SL_TYPE_INT:
            H5SL_REMOVE(SCALAR, slist, x, update, i, const int, key, checked)
            break;

        case H5SL_TYPE_HADDR:
            H5SL_REMOVE(SCALAR, slist, x, update, i, const haddr_t, key, checked)
            break;

        case H5SL_TYPE_STR:
            H5SL_REMOVE(STRING, slist, x, update, i, char *, key, checked)
            break;

        case H5SL_TYPE_HSIZE:
            H5SL_REMOVE(SCALAR, slist, x, update, i, const hsize_t, key, checked)
            break;

        case H5SL_TYPE_UNSIGNED:
            H5SL_REMOVE(SCALAR, slist, x, update, i, const unsigned, key, checked)
            break;

        case H5SL_TYPE_SIZE:
            H5SL_REMOVE(SCALAR, slist, x, update, i, const size_t, key, checked)
            break;

        case H5SL_TYPE_OBJ:
            H5SL_REMOVE(OBJ, slist, x, update, i, const H5_obj_t, key, checked)
            break;
    } /* end switch */

done:
    FUNC_LEAVE_NOAPI(ret_value);
} /* end H5SL_remove() */


/*--------------------------------------------------------------------------
 NAME
    H5SL_remove_first
 PURPOSE
    Removes the first object from a skip list
 USAGE
    void *H5SL_remove_first(slist)
        H5SL_t *slist;          IN/OUT: Pointer to skip list

 RETURNS
    Returns pointer to item removed on success, NULL on failure.
 DESCRIPTION
    Remove first element from a skip list.
 GLOBAL VARIABLES
 COMMENTS, BUGS, ASSUMPTIONS
    This algorithm is basically the same as the one in the
        H5SL_LOCATE_REMOVE_FOUND macro, fix bugs in both places
 EXAMPLES
 REVISION LOG
--------------------------------------------------------------------------*/
void *
H5SL_remove_first(H5SL_t *slist)
{
    void *ret_value = NULL;                     /* Return value */

    FUNC_ENTER_NOAPI_NOINIT_NOFUNC(H5SL_remove_first)

    /* Check args */
    HDassert(slist);

    /* Check internal consistency */
    /* (Pre-condition) */

    /* Remove item from skip list */

    /* Check for empty list */
    if(slist->last != slist->header) {
        H5SL_node_t *x;                             /* Current node to examine */
        int i;                                      /* Local index value */

        /* Get pointer to first node on the list */
        x = slist->header->forward[0];

        /* Patch forward pointers in list header around node to remove */
        for(i = 0; i <= (int)slist->curr_level; i++) {
            if(slist->header->forward[i] != x)
                break;
            slist->header->forward[i] = x->forward[i];
        } /* end for */

        /* Update tail/backward pointer */
        if(slist->last == x)
            slist->last = x->backward;
        else
            x->forward[0]->backward = x->backward;

        /* Get the item to return */
        ret_value = x->item;

        /* Free the skip list node */
        H5FL_ARR_FREE(H5SL_node_ptr_t, x);

        /* Lower the level of the list, if we removed the tallest node */
        while(slist->curr_level > 0 && slist->header->forward[slist->curr_level] == NULL)
            slist->curr_level--;

        /* Decrement the # of objects in the list */
        slist->nobjs--;
    } /* end if */

    FUNC_LEAVE_NOAPI(ret_value)
} /* end H5SL_remove_first() */


/*--------------------------------------------------------------------------
 NAME
    H5SL_search
 PURPOSE
    Search for object in a skip list
 USAGE
    void *H5SL_search(slist,key)
        H5SL_t *slist;          IN/OUT: Pointer to skip list
        void *key;              IN: Key for item to search for

 RETURNS
    Returns pointer to item on success, NULL on failure
 DESCRIPTION
    Search for an object in a skip list, according to it's key
 GLOBAL VARIABLES
 COMMENTS, BUGS, ASSUMPTIONS
 EXAMPLES
 REVISION LOG
--------------------------------------------------------------------------*/
void *
H5SL_search(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 */
    void *ret_value;                            /* Return value */

    FUNC_ENTER_NOAPI_NOINIT_NOFUNC(H5SL_search);

    /* 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_SEARCH(SCALAR, slist, x, -, i, const int, key, checked)
            break;

        case H5SL_TYPE_HADDR:
            H5SL_SEARCH(SCALAR, slist, x, -, i, const haddr_t, key, checked)
            break;

        case H5SL_TYPE_STR:
            H5SL_SEARCH(STRING, slist, x, -, i, char *, key, checked)
            break;

        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;

        case H5SL_TYPE_SIZE:
            H5SL_SEARCH(SCALAR, slist, x, -, i, const size_t, key, checked)
            break;

        case H5SL_TYPE_OBJ:
            H5SL_SEARCH(OBJ, slist, x, -, i, const H5_obj_t, 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_search() */


/*--------------------------------------------------------------------------
 NAME
    H5SL_less
 PURPOSE
    Search for object in a skip list that is less than or equal to 'key'
 USAGE
    void *H5SL_less(slist,key)
        H5SL_t *slist;          IN/OUT: Pointer to skip list
        void *key;              IN: Key for item to search for

 RETURNS
    Returns pointer to item who key is less than or equal to 'key' on success,
        NULL on failure
 DESCRIPTION
    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_less(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 */
    void *ret_value;                            /* Return value */

    FUNC_ENTER_NOAPI_NOINIT_NOFUNC(H5SL_less);

    /* 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_SEARCH(SCALAR, slist, x, -, i, const int, key, checked)
            break;

        case H5SL_TYPE_HADDR:
            H5SL_SEARCH(SCALAR, slist, x, -, i, const haddr_t, key, checked)
            break;

        case H5SL_TYPE_STR:
            H5SL_SEARCH(STRING, slist, x, -, i, char *, key, checked)
            break;

        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;

        case H5SL_TYPE_SIZE:
            H5SL_SEARCH(SCALAR, slist, x, -, i, const size_t, key, checked)
            break;

        case H5SL_TYPE_OBJ:
            H5SL_SEARCH(OBJ, slist, x, -, i, const H5_obj_t, 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_less() */


/*--------------------------------------------------------------------------
 NAME
    H5SL_greater
 PURPOSE
    Search for object in a skip list that is greater than or equal to 'key'
 USAGE
    void *H5SL_greater(slist, key)
        H5SL_t *slist;          IN/OUT: Pointer to skip list
        void *key;              IN: Key for item to search for

 RETURNS
    Returns pointer to item who key is greater than or equal to 'key' on success,
        NULL on failure
 DESCRIPTION
    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 lowest
    key that is greater than 'key'
 GLOBAL VARIABLES
 COMMENTS, BUGS, ASSUMPTIONS
 EXAMPLES
 REVISION LOG
--------------------------------------------------------------------------*/
void *
H5SL_greater(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 */
    void *ret_value;                            /* Return value */

    FUNC_ENTER_NOAPI_NOINIT_NOFUNC(H5SL_greater);

    /* Check args */
    HDassert(slist);
    HDassert(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_SEARCH(SCALAR, slist, x, -, i, const int, key, checked)
            break;

        case H5SL_TYPE_HADDR:
            H5SL_SEARCH(SCALAR, slist, x, -, i, const haddr_t, key, checked)
            break;

        case H5SL_TYPE_STR:
            H5SL_SEARCH(STRING, slist, x, -, i, char *, key, checked)
            break;

        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;

        case H5SL_TYPE_SIZE:
            H5SL_SEARCH(SCALAR, slist, x, -, i, const size_t, key, checked)
            break;

        case H5SL_TYPE_OBJ:
            H5SL_SEARCH(OBJ, slist, x, -, i, const H5_obj_t, key, checked)
            break;
    } /* end switch */

    /* An exact match for 'key' must not have been found in list, if we get here */
    /* ('x' must be the next node with a key greater than the 'key', or NULL) */
    if(x)
        ret_value = x->item;
    else
        ret_value = NULL;

done:
    FUNC_LEAVE_NOAPI(ret_value);
} /* end H5SL_greater() */


/*--------------------------------------------------------------------------
 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;

        case H5SL_TYPE_SIZE:
            H5SL_FIND(SCALAR, slist, x, -, i, const size_t, key, checked)
            break;

        case H5SL_TYPE_OBJ:
            H5SL_FIND(OBJ, slist, x, -, i, const H5_obj_t, 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() */


/*--------------------------------------------------------------------------
 NAME
    H5SL_first
 PURPOSE
    Gets a pointer to the first node in a skip list
 USAGE
    H5SL_node_t *H5SL_first(slist)
        H5SL_t *slist;          IN: Pointer to skip list

 RETURNS
    Returns pointer to first node in skip list on success, NULL on failure.
 DESCRIPTION
    Retrieves a pointer to the first node in a skip list, for iterating over
    the list.
 GLOBAL VARIABLES
 COMMENTS, BUGS, ASSUMPTIONS
 EXAMPLES
 REVISION LOG
--------------------------------------------------------------------------*/
H5SL_node_t *
H5SL_first(H5SL_t *slist)
{
    FUNC_ENTER_NOAPI_NOINIT_NOFUNC(H5SL_first);

    /* Check args */
    assert(slist);

    /* Check internal consistency */
    /* (Pre-condition) */

    FUNC_LEAVE_NOAPI(slist->header->forward[0]);
} /* end H5SL_first() */


/*--------------------------------------------------------------------------
 NAME
    H5SL_next
 PURPOSE
    Gets a pointer to the next node in a skip list
 USAGE
    H5SL_node_t *H5SL_next(slist_node)
        H5SL_node_t *slist_node;          IN: Pointer to skip list node

 RETURNS
    Returns pointer to node after slist_node in skip list on success, NULL on failure.
 DESCRIPTION
    Retrieves a pointer to the next node in a skip list, for iterating over
    the list.
 GLOBAL VARIABLES
 COMMENTS, BUGS, ASSUMPTIONS
 EXAMPLES
 REVISION LOG
--------------------------------------------------------------------------*/
H5SL_node_t *
H5SL_next(H5SL_node_t *slist_node)
{
    FUNC_ENTER_NOAPI_NOINIT_NOFUNC(H5SL_next);

    /* Check args */
    assert(slist_node);

    /* Check internal consistency */
    /* (Pre-condition) */

    FUNC_LEAVE_NOAPI(slist_node->forward[0]);
} /* end H5SL_next() */


/*--------------------------------------------------------------------------
 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 last 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
 USAGE
    void *H5SL_item(slist_node)
        H5SL_node_t *slist_node;          IN: Pointer to skip list node

 RETURNS
    Returns pointer to node 'item' on success, NULL on failure.
 DESCRIPTION
    Retrieves a node's 'item'
 GLOBAL VARIABLES
 COMMENTS, BUGS, ASSUMPTIONS
 EXAMPLES
 REVISION LOG
--------------------------------------------------------------------------*/
void *
H5SL_item(H5SL_node_t *slist_node)
{
    FUNC_ENTER_NOAPI_NOINIT_NOFUNC(H5SL_item);

    /* Check args */
    assert(slist_node);

    /* Check internal consistency */
    /* (Pre-condition) */

    FUNC_LEAVE_NOAPI(slist_node->item);
} /* end H5SL_item() */


/*--------------------------------------------------------------------------
 NAME
    H5SL_iterate
 PURPOSE
    Iterate over all nodes in a skip list
 USAGE
    herr_t H5SL_iterate(slist, op, op_data)
        H5SL_t *slist;          IN/OUT: Pointer to skip list to iterate over
        H5SL_operator_t op;     IN: Callback function for iteration
        void *op_data;          IN/OUT: Pointer to application data for callback

 RETURNS
    Returns a negative value if something is wrong, the return
        value of the last operator if it was non-zero, or zero if all
        nodes were processed.
 DESCRIPTION
    Iterate over all the nodes in a skip list, calling an application callback
    with the item, key and any operator data.

    The operator callback receives a pointer to the item and key for the list
    being iterated over ('mesg'), and the pointer to the operator data passed
    in to H5SL_iterate ('op_data').  The return values from an operator are:
        A. Zero causes the iterator to continue, returning zero when all
            nodes of that type have been processed.
        B. Positive causes the iterator to immediately return that positive
            value, indicating short-circuit success.
        C. Negative causes the iterator to immediately return that value,
            indicating failure.
 GLOBAL VARIABLES
 COMMENTS, BUGS, ASSUMPTIONS
 EXAMPLES
 REVISION LOG
--------------------------------------------------------------------------*/
herr_t
H5SL_iterate(H5SL_t *slist, H5SL_operator_t op, void *op_data)
{
    H5SL_node_t *node;  /* Pointers to skip list nodes */
    herr_t ret_value=0; /* Return value */

    FUNC_ENTER_NOAPI_NOINIT_NOFUNC(H5SL_iterate);

    /* Check args */
    assert(slist);

    /* Check internal consistency */
    /* (Pre-condition) */

    /* Free skip list nodes */
    node=slist->header->forward[0];
    while(node!=NULL) {
        /* Call the iterator callback */
        /* Casting away const OK -QAK */
        if((ret_value=(op)(node->item,(void *)node->key,op_data))!=0)
            break;

        node=node->forward[0];
    } /* end while */

    FUNC_LEAVE_NOAPI(ret_value);
} /* end H5SL_iterate() */


/*--------------------------------------------------------------------------
 NAME
    H5SL_release
 PURPOSE
    Release all nodes from a skip list
 USAGE
    herr_t H5SL_release(slist)
        H5SL_t *slist;            IN/OUT: Pointer to skip list to release nodes

 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
    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)
{
    FUNC_ENTER_NOAPI_NOINIT_NOFUNC(H5SL_release);

    /* Check args */
    assert(slist);

    /* Check internal consistency */
    /* (Pre-condition) */

    /* Free skip list nodes */
    H5SL_release_common(slist,NULL,NULL); /* always succeeds */

    FUNC_LEAVE_NOAPI(SUCCEED);
} /* end H5SL_release() */


/*--------------------------------------------------------------------------
 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_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() */


/*--------------------------------------------------------------------------
 NAME
    H5SL_close
 PURPOSE
    Close a skip list, deallocating it.
 USAGE
    herr_t H5SL_close(slist)
        H5SL_t *slist;            IN/OUT: Pointer to skip list to close

 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 are not deallocated.
 GLOBAL VARIABLES
 COMMENTS, BUGS, ASSUMPTIONS
 EXAMPLES
 REVISION LOG
--------------------------------------------------------------------------*/
herr_t
H5SL_close(H5SL_t *slist)
{
    FUNC_ENTER_NOAPI_NOINIT_NOFUNC(H5SL_close);

    /* Check args */
    assert(slist);

    /* Check internal consistency */
    /* (Pre-condition) */

    /* Close skip list */
    (void)H5SL_close_common(slist,NULL,NULL); /* always succeeds */

    FUNC_LEAVE_NOAPI(SUCCEED);
} /* end H5SL_close() */