realloc.c (1175B)
1 #include <stdlib.h> 2 #include <string.h> 3 4 #include "malloc.h" 5 #undef realloc 6 7 void * 8 realloc(void *ptr, size_t nbytes) 9 { 10 Header *oh, *prev, *next, *new; 11 size_t nunits, avail, onbytes, n; 12 13 if (!nbytes) 14 return NULL; 15 16 if (!ptr) 17 return malloc(nbytes); 18 19 nunits = (nbytes + sizeof(Header) - 1) / sizeof(Header) + 1; 20 oh = (Header*)ptr - 1; 21 22 if (oh->h.size == nunits) 23 return ptr; 24 25 new = oh + nunits; 26 27 if (nunits < oh->h.size - 1) { 28 new->h.size = oh->h.size - nunits; 29 oh->h.size = nunits; 30 free(new + 1); 31 return oh; 32 } 33 34 prev = _prevchunk(oh); 35 36 if (oh + oh->h.size == prev->h.next) { 37 /* 38 * if there is free space adjacent 39 * to the current memory 40 */ 41 next = prev->h.next; 42 avail = oh->h.size + next->h.size; 43 44 if (avail == nunits) { 45 oh->h.size = nunits; 46 prev->h.next = next->h.next; 47 return oh; 48 } 49 50 if (avail > nunits) { 51 oh->h.size = nunits; 52 prev->h.next = new; 53 new->h.next = next; 54 new->h.size = avail - nunits; 55 return oh; 56 } 57 } 58 59 onbytes = (oh->h.size - 1) * sizeof(Header); 60 if ((new = malloc(nbytes)) == NULL) 61 return NULL; 62 63 n = (onbytes > nbytes) ? nbytes : onbytes; 64 memcpy(new, ptr, n); 65 free(ptr); 66 67 return new; 68 }