file reorg, pathnames.h, paths.h

[unix-history] / usr / src / usr.bin / uucp / uucico / chksum.c

#ifndef lint
static char sccsid[] = "@(#)chksum.c    4.2 (Berkeley) %G%";
#endif

#ifndef pdp11
chksum (s, n)
register char *s;
register n;
{
       register long sum, x, t;

       sum = 0xffff;
       x = 0;
       do {
               /* Rotate left, copying bit 15 to bit 0 */
               sum <<= 1;
               if (sum & 0x10000)
                       sum ^= 0x10001;
               t = sum;
               sum = (sum + (*s++ & 0377)) & 0xffff;
               x += sum ^ n;
               if (sum <= t)
                       sum = (sum ^ x) & 0xffff;
       } while (--n > 0);

       return (long) (short) sum;
}
#else pdp11
chksum(s,n)
register char *s;
register n;
{
       register unsigned sum, t;
       register x;

       sum = -1;
       x = 0;

       do {
               if (sum&0x8000) {
                       sum <<= 1;
                       sum++;
               } else
                       sum <<= 1;
               t = sum;
               sum += (unsigned)*s++ & 0377;
               x += sum^n;
               if ((sum&0xffff) <= (t&0xffff)) {
                       sum ^= x;
               }
       } while (--n > 0);

       return sum & 0xffff;
}

#endif pdp11