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/*
* free.c
*
* Very simple linked-list based malloc()/free().
*/
#include <stdlib.h>
#include "malloc.h"
static struct free_arena_header *__free_block(struct free_arena_header *ah)
{
struct free_arena_header *pah, *nah;
pah = ah->a.prev;
nah = ah->a.next;
if (pah->a.type == ARENA_TYPE_FREE &&
(char *)pah + pah->a.size == (char *)ah) {
/* Coalesce into the previous block */
pah->a.size += ah->a.size;
pah->a.next = nah;
nah->a.prev = pah;
#ifdef DEBUG_MALLOC
ah->a.type = ARENA_TYPE_DEAD;
#endif
ah = pah;
pah = ah->a.prev;
} else {
/* Need to add this block to the free chain */
ah->a.type = ARENA_TYPE_FREE;
ah->next_free = __malloc_head.next_free;
ah->prev_free = &__malloc_head;
__malloc_head.next_free = ah;
ah->next_free->prev_free = ah;
}
/* In either of the previous cases, we might be able to merge
with the subsequent block... */
if (nah->a.type == ARENA_TYPE_FREE &&
(char *)ah + ah->a.size == (char *)nah) {
ah->a.size += nah->a.size;
/* Remove the old block from the chains */
nah->next_free->prev_free = nah->prev_free;
nah->prev_free->next_free = nah->next_free;
ah->a.next = nah->a.next;
nah->a.next->a.prev = ah;
#ifdef DEBUG_MALLOC
nah->a.type = ARENA_TYPE_DEAD;
#endif
}
/* Return the block that contains the called block */
return ah;
}
/*
* This is used to insert a block which is not previously on the
* free list. Only the a.size field of the arena header is assumed
* to be valid.
*/
void __inject_free_block(struct free_arena_header *ah)
{
struct free_arena_header *nah;
size_t a_end = (size_t) ah + ah->a.size;
size_t n_end;
for (nah = __malloc_head.a.next; nah->a.type != ARENA_TYPE_HEAD;
nah = nah->a.next) {
n_end = (size_t) nah + nah->a.size;
/* Is nah entirely beyond this block? */
if ((size_t) nah >= a_end)
break;
/* Is this block entirely beyond nah? */
if ((size_t) ah >= n_end)
continue;
/* Otherwise we have some sort of overlap - reject this block */
return;
}
/* Now, nah should point to the successor block */
ah->a.next = nah;
ah->a.prev = nah->a.prev;
nah->a.prev = ah;
ah->a.prev->a.next = ah;
__free_block(ah);
}
void free(void *ptr)
{
struct free_arena_header *ah;
if (!ptr)
return;
ah = (struct free_arena_header *)
((struct arena_header *)ptr - 1);
#ifdef DEBUG_MALLOC
assert(ah->a.type == ARENA_TYPE_USED);
#endif
__free_block(ah);
/* Here we could insert code to return memory to the system. */
}
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