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 #ifdef DEBUG
  72         len -= mlen;
  73 #endif
  74         /*
  75          * Force to even boundary.
  76          */
  77         if ((1 & (long) w) && (mlen > 0)) {
  78                 REDUCE;
  79                 sum <<= 8;
  80                 s_util.c[0] = *(u_int8_t *)w;
  81                 w = (u_int16_t *)((int8_t *)w + 1);
  82                 mlen--;
  83                 byte_swapped = 1;
  84         }
  85         /*
  86          * Unroll the loop to make overhead from
  87          * branches &c small.
  88          */
  89         while ((mlen -= 32) >= 0) {
  90                 sum += w[0]; sum += w[1]; sum += w[2]; sum += w[3];
  91                 sum += w[4]; sum += w[5]; sum += w[6]; sum += w[7];
  92                 sum += w[8]; sum += w[9]; sum += w[10]; sum += w[11];
  93                 sum += w[12]; sum += w[13]; sum += w[14]; sum += w[15];
  94                 w += 16;
  95         }
  96         mlen += 32;
  97         while ((mlen -= 8) >= 0) {
  98                 sum += w[0]; sum += w[1]; sum += w[2]; sum += w[3];
  99                 w += 4;
 100         }
 101         mlen += 8;
 102         if (mlen == 0 && byte_swapped == 0)
 103            goto cont;
 104         REDUCE;
 105         while ((mlen -= 2) >= 0) {
 106                 sum += *w++;
 107         }
 108
 109         if (byte_swapped) {
 110                 REDUCE;
 111                 sum <<= 8;
 112                 byte_swapped = 0;
 113                 if (mlen == -1) {
 114                         s_util.c[1] = *(u_int8_t *)w;
 115                         sum += s_util.s;
 116                         mlen = 0;
 117                 } else
 118
 119                    mlen = -1;
 120         } else if (mlen == -1)
 121            s_util.c[0] = *(u_int8_t *)w;
 122
 123 cont:
 124 #ifdef DEBUG
 125         if (len) {
 126                 DEBUG_ERROR((dfd, "cksum: out of data\n"));
 127                 DEBUG_ERROR((dfd, " len = %d\n", len));
 128         }
 129 #endif
 130         if (mlen == -1) {
 131                 /* The last mbuf has odd # of bytes. Follow the
 132                  standard (the odd byte may be shifted left by 8 bits
 133                            or not as determined by endian-ness of the machine) */
 134                 s_util.c[1] = 0;
 135                 sum += s_util.s;
 136         }
 137         REDUCE;
 138         return (~sum & 0xffff);
 139 }