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cksum.c

/*
 * Copyright (c) 1988, 1992, 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.
 *
 *    @(#)in_cksum.c    8.1 (Berkeley) 6/10/93
 * in_cksum.c,v 1.2 1994/08/02 07:48:16 davidg Exp
 */

#include <slirp.h>

/*
 * Checksum routine for Internet Protocol family headers (Portable Version).
 *
 * This routine is very heavily used in the network
 * code and should be modified for each CPU to be as fast as possible.
 *
 * XXX Since we will never span more than 1 mbuf, we can optimise this
 */

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

int cksum(struct mbuf *m, int len)
{
      register u_int16_t *w;
      register int sum = 0;
      register int mlen = 0;
      int byte_swapped = 0;

      union {
            u_int8_t    c[2];
            u_int16_t   s;
      } s_util;
      union {
            u_int16_t s[2];
            u_int32_t l;
      } l_util;

      if (m->m_len == 0)
         goto cont;
      w = mtod(m, u_int16_t *);

      mlen = m->m_len;

      if (len < mlen)
         mlen = len;
      len -= mlen;
      /*
       * Force to even boundary.
       */
      if ((1 & (long) w) && (mlen > 0)) {
            REDUCE;
            sum <<= 8;
            s_util.c[0] = *(u_int8_t *)w;
            w = (u_int16_t *)((int8_t *)w + 1);
            mlen--;
            byte_swapped = 1;
      }
      /*
       * Unroll the loop to make overhead from
       * branches &c small.
       */
      while ((mlen -= 32) >= 0) {
            sum += w[0]; sum += w[1]; sum += w[2]; sum += w[3];
            sum += w[4]; sum += w[5]; sum += w[6]; sum += w[7];
            sum += w[8]; sum += w[9]; sum += w[10]; sum += w[11];
            sum += w[12]; sum += w[13]; sum += w[14]; sum += w[15];
            w += 16;
      }
      mlen += 32;
      while ((mlen -= 8) >= 0) {
            sum += w[0]; sum += w[1]; sum += w[2]; sum += w[3];
            w += 4;
      }
      mlen += 8;
      if (mlen == 0 && byte_swapped == 0)
         goto cont;
      REDUCE;
      while ((mlen -= 2) >= 0) {
            sum += *w++;
      }

      if (byte_swapped) {
            REDUCE;
            sum <<= 8;
            byte_swapped = 0;
            if (mlen == -1) {
                  s_util.c[1] = *(u_int8_t *)w;
                  sum += s_util.s;
                  mlen = 0;
            } else

               mlen = -1;
      } else if (mlen == -1)
         s_util.c[0] = *(u_int8_t *)w;

cont:
#ifdef DEBUG
      if (len) {
            DEBUG_ERROR((dfd, "cksum: out of data\n"));
            DEBUG_ERROR((dfd, " len = %d\n", len));
      }
#endif
      if (mlen == -1) {
            /* The last mbuf has odd # of bytes. Follow the
             standard (the odd byte may be shifted left by 8 bits
                     or not as determined by endian-ness of the machine) */
            s_util.c[1] = 0;
            sum += s_util.s;
      }
      REDUCE;
      return (~sum & 0xffff);
}

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