git.gag.com Git - fw/sdcc/blob - device/lib/pic16/libc/stdlib/malloc.c

   1 /*
   2  * malloc.c - dynamic memory allocation
   3  *
   4  * written by Vangelis Rokas, 2004 (vrokas@otenet.gr)
   5  *
   6  */
   7
   8 #include "malloc.h"
   9
  10 extern unsigned char *_dynamicHeap;                     /* pointer to heap */
  11
  12 unsigned char *malloc(unsigned char len)
  13 {
  14   _malloc_rec *pHeap;                   /* pointer to block header */
  15   _malloc_rec *temp;
  16   unsigned char bLen;                   /* size of block  */
  17   unsigned char eLen;
  18
  19         if(len > _MAX_HEAP_SIZE)
  20                 return ((unsigned char *)0);
  21
  22         pHeap = (_malloc_rec *)&_dynamicHeap;
  23
  24
  25         while(1) {
  26                 bLen = pHeap->bits.count;
  27
  28                 /* if datum is zero, then last block, return NULL */
  29                 if(pHeap->datum == 0)
  30                         return ((unsigned char *)0);
  31
  32                 /* if current block is allocated then proceed to next */
  33                 if(pHeap->bits.alloc) {
  34                         pHeap += pHeap->bits.count;
  35                         continue;
  36                 }
  37
  38
  39                 /* current block is not allocated, try to allocate */
  40
  41                 /* if current block is not enough for allocation, then proceed to next */
  42                 if(bLen <= len) {
  43
  44                         /* current block is not enough see if we can merge some adjacent
  45                          * memory blocks to make it fit */
  46                         temp = pHeap + pHeap->bits.count;
  47                         eLen = bLen;
  48                         while((temp->datum) && (!temp->bits.alloc) && (eLen < len)) {
  49                                 eLen += temp->bits.count;
  50                                 temp += temp->bits.count;
  51                         }
  52
  53                         if(eLen >= len) {
  54                           int i;
  55                                 /* yes, there are some free blocks that can be merged, merge them... */
  56
  57                                 temp = pHeap;
  58                             while(eLen > 0) {
  59                                         if(eLen > MAX_BLOCK_SIZE)i = MAX_BLOCK_SIZE;
  60                                         else i = eLen;
  61
  62                                         temp->bits.count = i;
  63                                         temp->bits.alloc = 0;
  64
  65                                         temp += i;
  66                                         eLen -= i;
  67                                 }
  68
  69                                 bLen = pHeap->bits.count;
  70                         } else {
  71                                 /* otherwise proceed with next block */
  72                                 pHeap += pHeap->bits.count;
  73                                 continue;
  74                         }
  75                 }
  76
  77
  78                 /* current block is enough to hold the new block */
  79
  80                 /* allocate by filling the fields */
  81                 pHeap->bits.count = len+1;
  82                 pHeap->bits.alloc = 1;
  83
  84                 if(bLen > len+1) {
  85                         /* if current block size is greater than the requested one,
  86                          * create a new empty block at the end of the newly allocated */
  87                         temp = pHeap + len+1;
  88                         temp->bits.count = bLen - len - 1;
  89                         temp->bits.alloc = 0;
  90                 }
  91
  92                 return ((unsigned char *)pHeap + 1);
  93         }
  94 }