slirp/cksum.c

   1 /*
   2  * Copyright (c) 1988, 1992, 1993
   3  *      The Regents of the University of California.  All rights reserved.
   4  *
   5  * Redistribution and use in source and binary forms, with or without
   6  * modification, are permitted provided that the following conditions
   7  * are met:
   8  * 1. Redistributions of source code must retain the above copyright
   9  *    notice, this list of conditions and the following disclaimer.
  10  * 2. Redistributions in binary form must reproduce the above copyright
  11  *    notice, this list of conditions and the following disclaimer in the
  12  *    documentation and/or other materials provided with the distribution.
  13  * 3. Neither the name of the University nor the names of its contributors
  14  *    may be used to endorse or promote products derived from this software
  15  *    without specific prior written permission.
  16  *
  17  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
  18  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  19  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  20  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
  21  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  22  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  23  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  24  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  25  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  26  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  27  * SUCH DAMAGE.
  28  *
  29  *      @(#)in_cksum.c  8.1 (Berkeley) 6/10/93
  30  * in_cksum.c,v 1.2 1994/08/02 07:48:16 davidg Exp
  31  */
  32
  33 #include <slirp.h>
  34
  35 /*
  36  * Checksum routine for Internet Protocol family headers (Portable Version).
  37  *
  38  * This routine is very heavily used in the network
  39  * code and should be modified for each CPU to be as fast as possible.
  40  *
  41  * XXX Since we will never span more than 1 mbuf, we can optimise this
  42  */
  43
  44 #define ADDCARRY(x)  (x > 65535 ? x -= 65535 : x)
  45 #define REDUCE {l_util.l = sum; sum = l_util.s[0] + l_util.s[1]; ADDCARRY(sum);}
  46
  47 int cksum(struct mbuf *m, int len)
  48 {
  49         register u_int16_t *w;
  50         register int sum = 0;
  51         register int mlen = 0;
  52         int byte_swapped = 0;
  53
  54         union {
  55                 u_int8_t        c[2];
  56                 u_int16_t       s;
  57         } s_util;
  58         union {
  59                 u_int16_t s[2];
  60                 u_int32_t l;
  61         } l_util;
  62
  63         if (m->m_len == 0)
  64            goto cont;
  65         w = mtod(m, u_int16_t *);
  66
  67         mlen = m->m_len;
  68
  69         if (len < mlen)
  70            mlen = len;
  71         len -= mlen;
  72         /*
  73          * Force to even boundary.
  74          */
  75         if ((1 & (long) w) && (mlen > 0)) {
  76                 REDUCE;
  77                 sum <<= 8;
  78                 s_util.c[0] = *(u_int8_t *)w;
  79                 w = (u_int16_t *)((int8_t *)w + 1);
  80                 mlen--;
  81                 byte_swapped = 1;
  82         }
  83         /*
  84          * Unroll the loop to make overhead from
  85          * branches &c small.
  86          */
  87         while ((mlen -= 32) >= 0) {
  88                 sum += w[0]; sum += w[1]; sum += w[2]; sum += w[3];
  89                 sum += w[4]; sum += w[5]; sum += w[6]; sum += w[7];
  90                 sum += w[8]; sum += w[9]; sum += w[10]; sum += w[11];
  91                 sum += w[12]; sum += w[13]; sum += w[14]; sum += w[15];
  92                 w += 16;
  93         }
  94         mlen += 32;
  95         while ((mlen -= 8) >= 0) {
  96                 sum += w[0]; sum += w[1]; sum += w[2]; sum += w[3];
  97                 w += 4;
  98         }
  99         mlen += 8;
 100         if (mlen == 0 && byte_swapped == 0)
 101            goto cont;
 102         REDUCE;
 103         while ((mlen -= 2) >= 0) {
 104                 sum += *w++;
 105         }
 106
 107         if (byte_swapped) {
 108                 REDUCE;
 109                 sum <<= 8;
 110                 byte_swapped = 0;
 111                 if (mlen == -1) {
 112                         s_util.c[1] = *(u_int8_t *)w;
 113                         sum += s_util.s;
 114                         mlen = 0;
 115                 } else
 116
 117                    mlen = -1;
 118         } else if (mlen == -1)
 119            s_util.c[0] = *(u_int8_t *)w;
 120
 121 cont:
 122 #ifdef DEBUG
 123         if (len) {
 124                 DEBUG_ERROR((dfd, "cksum: out of data\n"));
 125                 DEBUG_ERROR((dfd, " len = %d\n", len));
 126         }
 127 #endif
 128         if (mlen == -1) {
 129                 /* The last mbuf has odd # of bytes. Follow the
 130                  standard (the odd byte may be shifted left by 8 bits
 131                            or not as determined by endian-ness of the machine) */
 132                 s_util.c[1] = 0;
 133                 sum += s_util.s;
 134         }
 135         REDUCE;
 136         return (~sum & 0xffff);
 137 }