usr/src/usr.bin/cksum/sum1.c

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

#ifndef lint
static char sccsid[] = "@(#)sum1.c      5.1 (Berkeley) %G%";
#endif /* not lint */

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

csum1(fd, cval, clen)
        register int fd;
        u_long *cval, *clen;
{
        register u_long total;
        register int nr;
        register u_int crc;
        register u_char *p;
        u_char buf[8192];

        /*
         * 16-bit checksum, rotating right before each addition;
         * overflow is discarded.
         */
        crc = total = 0;
        while ((nr = read(fd, buf, sizeof(buf))) > 0)
                for (total += nr, p = buf; nr--; ++p) {
                        if (crc & 1)
                                crc |= 0x10000;
                        crc = ((crc >> 1) + *p) & 0xffff;
                }
        if (nr < 0)
                return(1);

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