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#include <errno.h>
#include <stdckdint.h>
#include <string.h>
#include "alloc.h"
#include "macros.h"
void *
arena_realloc(arena *a, void *ptr, size_t old, size_t new, size_t elemsz,
size_t align)
{
ASSUME(a != nullptr);
if (ptr == nullptr)
return arena_alloc(a, new, elemsz, align);
if (old == new)
return ptr;
struct _region *cur = a->_head;
while (cur != nullptr) {
if (ptr >= cur->data && (char *)ptr < (char *)cur->data + cur->cap)
break;
cur = cur->next;
}
if (cur == nullptr)
cur = a->_head;
/* cur now points to the region containing ‘ptr’ */
/* If we are shrinking the buffer, then we don’t need to move our allocation
and can just return it directly. As a minor optimization if the
allocation we are shrinking is the last allocation in the current region,
we can decrease the region length to make space for more future
allocations. */
if (old > new) {
if (ptr == cur->last)
cur->len -= (old - new) * elemsz;
return ptr;
}
ASSUME(old < new);
/* If we need to grow the given allocation, but it was the last allocation
made in a region, then we first see if we can just eat more trailing free
space in the region to avoid a memcpy(). */
if (ptr == cur->last) {
size_t need, free = cur->cap - cur->len;
if (ckd_mul(&need, new - old, elemsz)) {
errno = EOVERFLOW;
return nullptr;
}
if (need <= free) {
cur->len += need;
return ptr;
}
}
/* At this point we just make a new allocation and copy the data over */
void *dst = arena_alloc(a, new, elemsz, align);
return dst == nullptr ? nullptr : memcpy(dst, ptr, old * elemsz);
}
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