realloc.c

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/*
 * realloc.c - dynamic memory allocation
 *
 * written by Vangelis Rokas, 2004 ([e-mail])
 *
 * This program is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License as published by the
 * Free Software Foundation; either version 2, or (at your option) any
 * later version.
 * 
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 * 
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
 * 
 * In other words, you are welcome to use, share and improve this program.
 * You are forbidden to forbid anyone else to use, share and improve
 * what you give them.   Help stamp out software-hoarding!  
 *
 * $Id: realloc.c 3835 2005-08-07 20:09:11Z tecodev $
 */

#include <malloc.h>

extern unsigned char _MALLOC_SPEC *heap;

unsigned char _MALLOC_SPEC *realloc(unsigned char _MALLOC_SPEC *mblock, unsigned char len)
{
  _malloc_rec _MALLOC_SPEC *pHeap;			/* pointer to block header */
  _malloc_rec _MALLOC_SPEC *temp;
  unsigned char bLen;			/* size of block  */

  if(len >= MAX_BLOCK_SIZE)
    return ((unsigned char _MALLOC_SPEC *)0);

  /* if mblock is NULL, then same as malloc */
  if(!mblock)
    return (malloc(len));

  /* if len is 0 */
  if(len == 0) {
    free(mblock);
    return ((unsigned char _MALLOC_SPEC *)0);
  }
  
  pHeap = (_malloc_rec _MALLOC_SPEC *)((unsigned int)mblock - 1);
  bLen = pHeap->bits.count;

  /* block too small for len bytes + 1 byte header <===> bLen < len + 1 <===> blen <= len */
  if (bLen <= len) {
    /* so, new segment has size bigger than the old one, we can return a
     * valid pointer only when after the block there is an empty block that
     * can be merged to produce a new block of the requested size, otherwise
     * we return NULL */
    temp = _mergeHeapBlock(pHeap, len);

    if(!temp) {
      /* no could not find a valid block, return NULL */
      return ((unsigned char _MALLOC_SPEC *)0);
    }

    //pHeap = temp; /* temp == pHeap */
    bLen = pHeap->bits.count;
  }

  len++; /* increase to also count the header */
  
  if(bLen > len) {
    /* new segment is smaller than the old one (or the merged one), that's easy! */
    pHeap->bits.count = len;
    temp = (_malloc_rec _MALLOC_SPEC *)((unsigned int)pHeap + len);
    temp->bits.alloc = 0;
    temp->bits.count = bLen - len;
  }

  return (mblock);
}