/*	$Id: compat_recallocarray.c,v 1.2 2020/06/15 01:37:15 schwarze Exp $ */
/*	$OpenBSD: recallocarray.c,v 1.1 2017/03/06 18:44:21 otto 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 "config.h"

#include <sys/types.h>
#include <errno.h>
#include <stdlib.h>
#include <stdint.h>
#include <string.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))

/*
 * Even though specified in POSIX, the PAGESIZE and PAGE_SIZE
 * macros have very poor portability.  Since we only use this
 * to avoid free() overhead for small shrinking, simply pick
 * an arbitrary number.
 */
#define getpagesize()	(1UL << 12)


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 < 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);

	/*
	 * At this point, the OpenBSD implementation calls
	 * explicit_bzero() on the old memory before it is
	 * freed.  Since explicit_bzero() is hard to implement
	 * portably and we don't handle confidential data in
	 * mandoc in the first place, simply free the memory
	 * without clearing it.
	 */

	free(ptr);

	return newptr;
}