sum2.c

/*-
 * SPDX-License-Identifier: BSD-3-Clause
 *
 * Copyright (c) 1991, 1993
 *	The Regents of the University of California.  All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. Neither the name of the University nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 */

#include <sys/types.h>

#include <unistd.h>
#include <stdint.h>

#include "extern.h"

int
csum2(int fd, uint32_t *cval, off_t *clen)
{
	uint32_t lcrc;
	int nr;
	off_t total;
	u_char *p;
	u_char buf[8192];

	/*
	 * Draft 8 POSIX 1003.2:
	 *
	 *   s = sum of all bytes
	 *   r = s % 2^16 + (s % 2^32) / 2^16
	 * lcrc = (r % 2^16) + r / 2^16
	 */
	lcrc = total = 0;
	while ((nr = read(fd, buf, sizeof(buf))) > 0)
		for (total += nr, p = buf; nr--; ++p)
			lcrc += *p;
	if (nr < 0)
		return (1);

	lcrc = (lcrc & 0xffff) + (lcrc >> 16);
	lcrc = (lcrc & 0xffff) + (lcrc >> 16);

	*cval = lcrc;
	*clen = total;
	return (0);
}