Suzy B Software 2/Suzy B Software CD-ROM 2 (1994).iso/extras/programm/gemfsc20/gemfsc20.lzh/EXAMPLES/BROWSE/DLLUTIL.C

Text File | 1992-12-07 | 5KB | 208 lines

/*****************************************************************************
 * DLLUTIL - Standard routines for handling double-linked lists.
 ****************************************************************************/

#define DLLUTIL_INTERNALS
#include "dllutil.h"

#ifndef NULL
  #define NULL ((void*)0)
#endif

#ifndef TRUE
  #define TRUE    1
  #define FALSE 0
#endif

#define DLL_DEBUG(statement)  /* statement */

void *dl_insert(list, afteritem, newitem)
/*****************************************************************************
 *
 ****************************************************************************/
    register DlList    *list;
    register DllHeader *afteritem;
    register DllHeader *newitem;
{
    if (NULL == list || NULL == afteritem || NULL == newitem) {
        DLL_DEBUG(printf("NULL item pointer: dl_insert(%p, %p, %p);\n", list, afteritem, newitem));
        return NULL;
    }

    newitem->prev    = afteritem;
    newitem->next    = afteritem->next;
    afteritem->next = newitem;

    if (NULL == newitem->next) {
        list->tail = newitem;
    } else {
        newitem->next->prev = newitem;
    }
    return newitem;
}

void *dl_addhead(list, item)
/*****************************************************************************
 *
 ****************************************************************************/
    register DlList    *list;
    register DllHeader *item;
{
    if (NULL == list || NULL == item) {
        DLL_DEBUG(printf("NULL list or item pointer: dl_addhead(%p, %p);\n", list, item));
        return NULL;
    }

    item->prev = NULL;            /* first item in list has NULL backlink     */
    item->next = list->head;    /* connect item's fwdlink to next item      */
    list->head = item;            /* connect item to list head                */

    if (NULL == item->next) {    /* if the item we just added is last/only    */
        list->tail = item;        /* item, connect it to the list tail        */
        list->cur  = item;        /* and to the current-item pointer            */
    } else {
        item->next->prev = item;/* else connect next item's backlink        */
    }

    return item;
}

void *dl_addtail(list, item)
/*****************************************************************************
 *
 ****************************************************************************/
    register DlList    *list;
    register DllHeader *item;
{
    if (NULL == list || NULL == item) {
        DLL_DEBUG(printf("NULL list or item pointer: dl_addtail(%p, %p);\n", list, item));
        return NULL;
    }

    if (NULL == list->tail) {
        return dl_addhead(list, item);
    } else {
        return dl_insert(list, list->tail, item);
    }

}

void dl_remove(list, item)
/*****************************************************************************
 *
 ****************************************************************************/
    register DlList    *list;
    register DllHeader *item;
{
    if (NULL == list || NULL == item) {
        DLL_DEBUG(printf("NULL list or item pointer: dl_remove(%p, %p);\n", list, item));
        return;
    }

    if (list->cur == item) {
        if (NULL == item->next) {
            list->cur = item->prev;
        } else {
            list->cur = item->next;
        }
    }

    if (NULL == item->next) {
        list->tail = item->prev;
    } else {
        item->next->prev = item->prev;
    }

    if (NULL == item->prev) {
        list->head = item->next;
    } else {
        item->prev->next = item->next;
    }

}

void dl_freelist(list, freefunc)
/*****************************************************************************
 *
 ****************************************************************************/
    register DlList      *list;
#if __STDC__
    register void         (*freefunc)(DlList *, void *);
#else
    register void         (*freefunc)();
#endif
{
    register DllHeader     *cur, *next;

    for (cur = list->head; cur != NULL; cur = next) {
        next = cur->next;
        (*freefunc)(list, cur);
    }
}

int dl_seek(list, count, whence)
/*****************************************************************************
 * seek to an item in a list, kinda like fseek().
 * returns TRUE if at either end of the list, FALSE if not at end.
 ****************************************************************************/
    register DlList *list;
    register long    count;
    int             whence;
{
    register DllHeader    *cur, *next;
    register int        backwards;

    switch (whence) {
      case 0:
        cur = list->head;
        backwards = FALSE;
        break;
      default:
        DLL_DEBUG(printf("Unknown 'whence' type in dl_seek(), SEEK_CUR assumed.\n"));
        /* fall thru */
      case 1:
        cur = list->cur;
        backwards = (count < 0) ? TRUE : FALSE;
        break;
      case 2:
        cur = list->tail;
        backwards = TRUE;
        break;
    }

    if (NULL == cur)
        return TRUE;

    if (count < 0) {
        count = -count;
    }

    next = (backwards) ? cur->prev : cur->next;

    while (next && count) {
        cur  = next;
        next = (backwards) ? cur->prev : cur->next;
        --count;
    }

    list->cur = cur;
    return (next == NULL);
}

long dl_tell(list)
/*****************************************************************************
 * returns the index of the current item in the list.
 ****************************************************************************/
    register DlList *list;
{
    register DllHeader *cur = list->head;
    register long       idx    = 0;

    while (cur && cur != list->cur) {
        ++idx;
        cur = cur->next;
    }

    return idx;
}