1 /* 2 * free.c 3 * 4 * Very simple linked-list based malloc()/free(). 5 */ 6 7 #include <stdlib.h> 8 #include "malloc.h" 9 __free_block(struct free_arena_header * ah)10static struct free_arena_header *__free_block(struct free_arena_header *ah) 11 { 12 struct free_arena_header *pah, *nah; 13 14 pah = ah->a.prev; 15 nah = ah->a.next; 16 if (pah->a.type == ARENA_TYPE_FREE && 17 (char *)pah + pah->a.size == (char *)ah) { 18 /* Coalesce into the previous block */ 19 pah->a.size += ah->a.size; 20 pah->a.next = nah; 21 nah->a.prev = pah; 22 23 #ifdef DEBUG_MALLOC 24 ah->a.type = ARENA_TYPE_DEAD; 25 #endif 26 27 ah = pah; 28 pah = ah->a.prev; 29 } else { 30 /* Need to add this block to the free chain */ 31 ah->a.type = ARENA_TYPE_FREE; 32 33 ah->next_free = __malloc_head.next_free; 34 ah->prev_free = &__malloc_head; 35 __malloc_head.next_free = ah; 36 ah->next_free->prev_free = ah; 37 } 38 39 /* In either of the previous cases, we might be able to merge 40 with the subsequent block... */ 41 if (nah->a.type == ARENA_TYPE_FREE && 42 (char *)ah + ah->a.size == (char *)nah) { 43 ah->a.size += nah->a.size; 44 45 /* Remove the old block from the chains */ 46 nah->next_free->prev_free = nah->prev_free; 47 nah->prev_free->next_free = nah->next_free; 48 ah->a.next = nah->a.next; 49 nah->a.next->a.prev = ah; 50 51 #ifdef DEBUG_MALLOC 52 nah->a.type = ARENA_TYPE_DEAD; 53 #endif 54 } 55 56 /* Return the block that contains the called block */ 57 return ah; 58 } 59 free(void * ptr)60void free(void *ptr) 61 { 62 struct free_arena_header *ah; 63 64 if (!ptr) 65 return; 66 67 ah = (struct free_arena_header *) 68 ((struct arena_header *)ptr - 1); 69 70 __free_block(ah); 71 72 /* Here we could insert code to return memory to the system. */ 73 } 74