text: /*
   * 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);
  }
  