src/malloc/oldmalloc/aligned_alloc.c

#include <stdlib.h>
#include <stdint.h>
#include <errno.h>
#include "malloc_impl.h"

void *aligned_alloc(size_t align, size_t len)
{
	unsigned char *mem, *new;

	if ((align & -align) != align) {
		errno = EINVAL;
		return 0;
	}

	if (len > SIZE_MAX - align ||
	    (__malloc_replaced && !__aligned_alloc_replaced)) {
		errno = ENOMEM;
		return 0;
	}

	if (align <= SIZE_ALIGN)
		return malloc(len);

	if (!(mem = malloc(len + align-1)))
		return 0;

	new = (void *)((uintptr_t)mem + align-1 & -align);
	if (new == mem) return mem;

	struct chunk *c = MEM_TO_CHUNK(mem);
	struct chunk *n = MEM_TO_CHUNK(new);

	if (IS_MMAPPED(c)) {
		/* Apply difference between aligned and original
		 * address to the "extra" field of mmapped chunk. */
		n->psize = c->psize + (new-mem);
		n->csize = c->csize - (new-mem);
		return new;
	}

	struct chunk *t = NEXT_CHUNK(c);

	/* Split the allocated chunk into two chunks. The aligned part
	 * that will be used has the size in its footer reduced by the
	 * difference between the aligned and original addresses, and
	 * the resulting size copied to its header. A new header and
	 * footer are written for the split-off part to be freed. */
	n->psize = c->csize = C_INUSE | (new-mem);
	n->csize = t->psize -= new-mem;

	__bin_chunk(c);
	return new;
}