usr/src/sys/netns/ns_cksum.c

/*
 * Copyright (c) 1982, 1988 Regents of the University of California.
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms are permitted
 * provided that this notice is preserved and that due credit is given
 * to the University of California at Berkeley. The name of the University
 * may not be used to endorse or promote products derived from this
 * software without specific prior written permission. This software
 * is provided ``as is'' without express or implied warranty.
 *
 *      @(#)ns_cksum.c  1.3 (Berkeley) %G%
 */
#include "types.h"
#include "mbuf.h"
/*
 * Checksum routine for Network Systems Protocol Packets (Big-Endian).
 *
 * This routine is very heavily used in the network
 * code and should be modified for each CPU to be as fast as possible.
 */

#define ADDCARRY(x)  (x > 65535 ? x -= 65535 : x)
#define FOLD(x) {l_util.l = x; x = l_util.s[0] + l_util.s[1]; ADDCARRY(x);}

u_short
ns_cksum(m, len)
        register struct mbuf *m;
        register int len;
{
        register u_short *w;
        register int sum = 0;
        register int mlen = 0;
        register int sum2;

        union {
                u_short s[2];
                long    l;
        } l_util;

        for (;m && len; m = m->m_next) {
                if (m->m_len == 0)
                        continue;
                /*
                 * Each trip around loop adds in
                 * word from one mbuf segment.
                 */
                w = mtod(m, u_short *);
                if (mlen == -1) {
                        /*
                         * There is a byte left from the last segment;
                         * ones-complement add it into the checksum.
                         */
                        sum  += *(u_char *)w; /* Big-Endian, else << 8 */
                        sum += sum;
                        w = (u_short *)(1 + (char *)w);
                        mlen = m->m_len - 1;
                        len--;
                        FOLD(sum);
                } else
                        mlen = m->m_len;
                if (len < mlen)
                        mlen = len;
                len -= mlen;
                /*
                 * We can do a 16 bit ones complement sum using
                 * 32 bit arithmetic registers for adding,
                 * with carries from the low added
                 * into the high (by normal carry-chaining)
                 * so long as we fold back before 16 carries have occured.
                 */
                if (1 & (int) w)
                        goto uuuuglyy;
#ifndef TINY
/* -DTINY reduces the size from 1250 to 550, but slows it down by 22% */
                while ((mlen -= 32) >= 0) {
                        sum += w[0]; sum += sum; sum += w[1]; sum += sum;
                        sum += w[2]; sum += sum; sum += w[3]; sum += sum;
                        sum += w[4]; sum += sum; sum += w[5]; sum += sum;
                        sum += w[6]; sum += sum; sum += w[7]; sum += sum;
                        FOLD(sum);
                        sum += w[8]; sum += sum; sum += w[9]; sum += sum;
                        sum += w[10]; sum += sum; sum += w[11]; sum += sum;
                        sum += w[12]; sum += sum; sum += w[13]; sum += sum;
                        sum += w[14]; sum += sum; sum += w[15]; sum += sum;
                        FOLD(sum);
                        w += 16;
                }
                mlen += 32;
#endif
                while ((mlen -= 8) >= 0) {
                        sum += w[0]; sum += sum; sum += w[1]; sum += sum;
                        sum += w[2]; sum += sum; sum += w[3]; sum += sum;
                        FOLD(sum);
                        w += 4;
                }
                mlen += 8;
                while ((mlen -= 2) >= 0) {
                        sum += *w++; sum += sum;
                }
                goto commoncase;
uuuuglyy:
/* Big-Endian; else reverse ww and vv */
#define ww(n) (((u_char *)w)[n + n + 1])
#define vv(n) (((u_char *)w)[n + n])
                sum2 = 0;
#ifndef TINY
                while ((mlen -= 32) >= 0) {
                    sum += ww(0); sum += sum; sum += ww(1); sum += sum;
                    sum += ww(2); sum += sum; sum += ww(3); sum += sum;
                    sum += ww(4); sum += sum; sum += ww(5); sum += sum;
                    sum += ww(6); sum += sum; sum += ww(7); sum += sum;
                    FOLD(sum);
                    sum += ww(8); sum += sum; sum += ww(9); sum += sum;
                    sum += ww(10); sum += sum; sum += ww(11); sum += sum;
                    sum += ww(12); sum += sum; sum += ww(13); sum += sum;
                    sum += ww(14); sum += sum; sum += ww(15); sum += sum;
                    FOLD(sum);
                    sum2 += vv(0); sum2 += sum2; sum2 += vv(1); sum2 += sum2;
                    sum2 += vv(2); sum2 += sum2; sum2 += vv(3); sum2 += sum2;
                    sum2 += vv(4); sum2 += sum2; sum2 += vv(5); sum2 += sum2;
                    sum2 += vv(6); sum2 += sum2; sum2 += vv(7); sum2 += sum2;
                    FOLD(sum2);
                    sum2 += vv(8); sum2 += sum2; sum2 += vv(9); sum2 += sum2;
                    sum2 += vv(10); sum2 += sum2; sum2 += vv(11); sum2 += sum2;
                    sum2 += vv(12); sum2 += sum2; sum2 += vv(13); sum2 += sum2;
                    sum2 += vv(14); sum2 += sum2; sum2 += vv(15); sum2 += sum2;
                    FOLD(sum2);
                    w += 16;
                }
                mlen += 32;
#endif
                while ((mlen -= 8) >= 0) {
                    sum += ww(0); sum += sum; sum += ww(1); sum += sum;
                    sum += ww(2); sum += sum; sum += ww(3); sum += sum;
                    FOLD(sum);
                    sum2 += vv(0); sum2 += sum2; sum2 += vv(1); sum2 += sum2;
                    sum2 += vv(2); sum2 += sum2; sum2 += vv(3); sum2 += sum2;
                    FOLD(sum2);
                    w += 4;
                }
                mlen += 8;
                while ((mlen -= 2) >= 0) {
                        sum += ww(0); sum += sum;
                        sum2 += vv(0); sum2 += sum2;
                        w++;
                }
                sum += (sum2 << 8);
commoncase:
                if (mlen == -1) {
                        sum += *(u_char *)w << 8; /* Big-Endian, else no << 8 */
                }
                FOLD(sum);
        }
        if (mlen == -1) {
                /* We had an odd number of bytes to sum; assume a garbage
                   byte of zero and clean up */
                sum += sum;
                FOLD(sum);
        }
        /*
         * sum has already been kept to low sixteen bits.
         * just examine result and exit.
         */
        if(sum==0xffff) sum = 0;
        return (sum);
}