/*      $OpenBSD: recallocarray.c,v 1.2 2021/03/18 11:16:58 claudio Exp $       */
/*
 * Copyright (c) 2008, 2017 Otto Moerbeek <otto@drijf.net>
 *
 * Permission to use, copy, modify, and distribute this software for any
 * purpose with or without fee is hereby granted, provided that the above
 * copyright notice and this permission notice appear in all copies.
 *
 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
 * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
 * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
 * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
 */

#include <errno.h>
#include <stdlib.h>
#include <stdint.h>
#include <string.h>
#include <unistd.h>

/*
 * This is sqrt(SIZE_MAX+1), as s1*s2 <= SIZE_MAX
 * if both s1 < MUL_NO_OVERFLOW and s2 < MUL_NO_OVERFLOW
 */
#define MUL_NO_OVERFLOW ((size_t)1 << (sizeof(size_t) * 4))

void *
recallocarray(void *ptr, size_t oldnmemb, size_t newnmemb, size_t size)
{
        size_t oldsize, newsize;
        void *newptr;

        if (ptr == NULL)
                return calloc(newnmemb, size);

        if ((newnmemb >= MUL_NO_OVERFLOW || size >= MUL_NO_OVERFLOW) &&
            newnmemb > 0 && SIZE_MAX / newnmemb < size) {
                errno = ENOMEM;
                return NULL;
        }
        newsize = newnmemb * size;

        if ((oldnmemb >= MUL_NO_OVERFLOW || size >= MUL_NO_OVERFLOW) &&
            oldnmemb > 0 && SIZE_MAX / oldnmemb < size) {
                errno = EINVAL;
                return NULL;
        }
        oldsize = oldnmemb * size;
        
        /*
         * Don't bother too much if we're shrinking just a bit,
         * we do not shrink for series of small steps, oh well.
         */
        if (newsize <= oldsize) {
                size_t d = oldsize - newsize;

                if (d < oldsize / 2 && d < (size_t)getpagesize()) {
                        memset((char *)ptr + newsize, 0, d);
                        return ptr;
                }
        }

        newptr = malloc(newsize);
        if (newptr == NULL)
                return NULL;

        if (newsize > oldsize) {
                memcpy(newptr, ptr, oldsize);
                memset((char *)newptr + oldsize, 0, newsize - oldsize);
        } else
                memcpy(newptr, ptr, newsize);

        explicit_bzero(ptr, oldsize);
        free(ptr);

        return newptr;
}
DEF_WEAK(recallocarray);