source: azure_iot_hub/trunk/musl-1.1.18/src/malloc/memalign.c@ 388

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

/* This function should work with most dlmalloc-like chunk bookkeeping
 * systems, but it's only guaranteed to work with the native implementation
 * used in this library. */

void *__memalign(size_t align, size_t len)
{
        unsigned char *mem, *new, *end;
        size_t header, footer;

        if ((align & -align) != 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;

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

        header = ((size_t *)mem)[-1];

        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;

        free(mem);
        return new;
}

weak_alias(__memalign, memalign);