usr/src/usr.bin/cksum/sum2.c

/*-
 * Copyright (c) 1991, 1993
 *      The Regents of the University of California.  All rights reserved.
 *
 * %sccs.include.redist.c%
 */

#ifndef lint
static char sccsid[] = "@(#)sum2.c      8.1 (Berkeley) %G%";
#endif /* not lint */

#include <sys/types.h>
#include <unistd.h>

int
csum2(fd, cval, clen)
        register int fd;
        u_long *cval, *clen;
{
        register u_long crc, total;
        register int nr;
        register 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
         * crc = (r % 2^16) + r / 2^16
         */
        crc = total = 0;
        while ((nr = read(fd, buf, sizeof(buf))) > 0)
                for (total += nr, p = buf; nr--; ++p)
                        crc += *p;
        if (nr < 0)
                return(1);

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

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