- unsigned char *mem, *new, *end;
- size_t header, footer;
-
- if ((align & -align & -sizeof(void *)) != align) {
- errno = EINVAL;
- return NULL;
- }
-
- if (len > SIZE_MAX - align) {
- errno = ENOMEM;
- return NULL;
- }
-
- if (align <= 4*sizeof(size_t)) {
- if (!(mem = malloc(len)))
- return NULL;
- return mem;
- }
-
- if (!(mem = malloc(len + align-1)))
- return NULL;
-
- header = ((size_t *)mem)[-1];
- new = (void *)((uintptr_t)mem + align-1 & -align);
-
- if (!(header & 7)) {
- ((size_t *)new)[-2] = ((size_t *)mem)[-2] + (new-mem);
- ((size_t *)new)[-1] = ((size_t *)mem)[-1] - (new-mem);
- return new;
- }
-
- end = mem + (header & -8);
- footer = ((size_t *)end)[-2];
-
- ((size_t *)mem)[-1] = header&7 | new-mem;
- ((size_t *)new)[-2] = footer&7 | new-mem;
- ((size_t *)new)[-1] = header&7 | end-new;
- ((size_t *)end)[-2] = footer&7 | end-new;
-
- if (new != mem) free(mem);
- return new;