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/*
* realloc.c
*/
#include <stdlib.h>
#include <string.h>
#include <minmax.h>
#include "malloc.h"
void *realloc(void *ptr, size_t size)
{
struct free_arena_header *ah, *nah;
void *newptr;
size_t newsize, oldsize, xsize;
if (!ptr)
return malloc(size);
if (size == 0) {
free(ptr);
return NULL;
}
ah = (struct free_arena_header *)
((struct arena_header *)ptr - 1);
/* Actual size of the old block */
oldsize = ah->a.size;
/* Add the obligatory arena header, and round up */
newsize = (size + 2 * sizeof(struct arena_header) - 1) & ARENA_SIZE_MASK;
if (oldsize >= newsize && newsize >= (oldsize >> 2) &&
oldsize - newsize < 4096) {
/* This allocation is close enough already. */
return ptr;
} else {
xsize = oldsize;
nah = ah->a.next;
if ((char *)nah == (char *)ah + ah->a.size &&
nah->a.type == ARENA_TYPE_FREE &&
oldsize + nah->a.size >= newsize) {
/* Merge in subsequent free block */
ah->a.next = nah->a.next;
ah->a.next->a.prev = ah;
nah->next_free->prev_free = nah->prev_free;
nah->prev_free->next_free = nah->next_free;
xsize = (ah->a.size += nah->a.size);
}
if (xsize >= newsize) {
/* We can reallocate in place */
if (xsize >= newsize + 2 * sizeof(struct arena_header)) {
/* Residual free block at end */
nah = (struct free_arena_header *)((char *)ah + newsize);
nah->a.type = ARENA_TYPE_FREE;
nah->a.size = xsize - newsize;
ah->a.size = newsize;
/* Insert into block list */
nah->a.next = ah->a.next;
ah->a.next = nah;
nah->a.next->a.prev = nah;
nah->a.prev = ah;
/* Insert into free list */
if (newsize > oldsize) {
/* Hack: this free block is in the path of a memory object
which has already been grown at least once. As such, put
it at the *end* of the freelist instead of the beginning;
trying to save it for future realloc()s of the same block. */
nah->prev_free = __malloc_head.prev_free;
nah->next_free = &__malloc_head;
__malloc_head.prev_free = nah;
nah->prev_free->next_free = nah;
} else {
nah->next_free = __malloc_head.next_free;
nah->prev_free = &__malloc_head;
__malloc_head.next_free = nah;
nah->next_free->prev_free = nah;
}
}
/* otherwise, use up the whole block */
return ptr;
} else {
/* Last resort: need to allocate a new block and copy */
oldsize -= sizeof(struct arena_header);
newptr = malloc(size);
if (newptr) {
memcpy(newptr, ptr, min(size, oldsize));
free(ptr);
}
return newptr;
}
}
}
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