text: /*	$OpenBSD: in_cksum.c,v 1.8 2015/07/17 23:49:03 tedu Exp $	*/
  /*	$NetBSD: in_cksum.c,v 1.11 1996/04/08 19:55:37 jonathan Exp $	*/
  
  /*
   * 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
   */
  
  #include <sys/param.h>
  #include <sys/mbuf.h>
  #include <sys/systm.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.
   */
  
  #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
  in_cksum(struct mbuf *m, int len)
  {
  	u_int16_t *w;
  	int sum = 0;
  	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;
  
  	for (;m && len; m = m->m_next) {
  		if (m->m_len == 0)
  			continue;
  		w = mtod(m, u_int16_t *);
  		if (mlen == -1) {
  			/*
  			 * The first byte of this mbuf is the continuation
  			 * of a word spanning between this mbuf and the
  			 * last mbuf.
  			 *
  			 * s_util.c[0] is already saved when scanning previous
  			 * mbuf.
  			 */
  			s_util.c[1] = *(u_int8_t *)w;
  			sum += s_util.s;
  			w = (u_int16_t *)((u_int8_t *)w + 1);
  			mlen = m->m_len - 1;
  			len--;
  		} else
  			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)
  			continue;
  		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;
  	}
  	if (len)
  		printf("cksum: out of data\n");
  	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);
  }
  