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    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: }