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in_cksum.c revision 1.9 
      1 /*	$NetBSD: in_cksum.c,v 1.9 1994/06/29 06:38:05 cgd Exp $	*/
      2 
      3 /*
      4  * Copyright (c) 1988, 1992, 1993
      5  *	The Regents of the University of California.  All rights reserved.
      6  *
      7  * Redistribution and use in source and binary forms, with or without
      8  * modification, are permitted provided that the following conditions
      9  * are met:
     10  * 1. Redistributions of source code must retain the above copyright
     11  *    notice, this list of conditions and the following disclaimer.
     12  * 2. Redistributions in binary form must reproduce the above copyright
     13  *    notice, this list of conditions and the following disclaimer in the
     14  *    documentation and/or other materials provided with the distribution.
     15  * 3. All advertising materials mentioning features or use of this software
     16  *    must display the following acknowledgement:
     17  *	This product includes software developed by the University of
     18  *	California, Berkeley and its contributors.
     19  * 4. Neither the name of the University nor the names of its contributors
     20  *    may be used to endorse or promote products derived from this software
     21  *    without specific prior written permission.
     22  *
     23  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
     24  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
     25  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
     26  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
     27  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
     28  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
     29  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
     30  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
     31  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
     32  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
     33  * SUCH DAMAGE.
     34  *
     35  *	@(#)in_cksum.c	8.1 (Berkeley) 6/10/93
     36  */
     37 
     38 #include <sys/param.h>
     39 #include <sys/mbuf.h>
     40 
     41 /*
     42  * Checksum routine for Internet Protocol family headers (Portable Version).
     43  *
     44  * This routine is very heavily used in the network
     45  * code and should be modified for each CPU to be as fast as possible.
     46  */
     47 
     48 #define ADDCARRY(x)  (x > 65535 ? x -= 65535 : x)
     49 #define REDUCE {l_util.l = sum; sum = l_util.s[0] + l_util.s[1]; ADDCARRY(sum);}
     50 
     51 int
     52 in_cksum(m, len)
     53 	register struct mbuf *m;
     54 	register int len;
     55 {
     56 	register u_short *w;
     57 	register int sum = 0;
     58 	register int mlen = 0;
     59 	int byte_swapped = 0;
     60 
     61 	union {
     62 		char	c[2];
     63 		u_short	s;
     64 	} s_util;
     65 	union {
     66 		u_short s[2];
     67 		long	l;
     68 	} l_util;
     69 
     70 	for (;m && len; m = m->m_next) {
     71 		if (m->m_len == 0)
     72 			continue;
     73 		w = mtod(m, u_short *);
     74 		if (mlen == -1) {
     75 			/*
     76 			 * The first byte of this mbuf is the continuation
     77 			 * of a word spanning between this mbuf and the
     78 			 * last mbuf.
     79 			 *
     80 			 * s_util.c[0] is already saved when scanning previous
     81 			 * mbuf.
     82 			 */
     83 			s_util.c[1] = *(char *)w;
     84 			sum += s_util.s;
     85 			w = (u_short *)((char *)w + 1);
     86 			mlen = m->m_len - 1;
     87 			len--;
     88 		} else
     89 			mlen = m->m_len;
     90 		if (len < mlen)
     91 			mlen = len;
     92 		len -= mlen;
     93 		/*
     94 		 * Force to even boundary.
     95 		 */
     96 		if ((1 & (int) w) && (mlen > 0)) {
     97 			REDUCE;
     98 			sum <<= 8;
     99 			s_util.c[0] = *(u_char *)w;
    100 			w = (u_short *)((char *)w + 1);
    101 			mlen--;
    102 			byte_swapped = 1;
    103 		}
    104 		/*
    105 		 * Unroll the loop to make overhead from
    106 		 * branches &c small.
    107 		 */
    108 		while ((mlen -= 32) >= 0) {
    109 			sum += w[0]; sum += w[1]; sum += w[2]; sum += w[3];
    110 			sum += w[4]; sum += w[5]; sum += w[6]; sum += w[7];
    111 			sum += w[8]; sum += w[9]; sum += w[10]; sum += w[11];
    112 			sum += w[12]; sum += w[13]; sum += w[14]; sum += w[15];
    113 			w += 16;
    114 		}
    115 		mlen += 32;
    116 		while ((mlen -= 8) >= 0) {
    117 			sum += w[0]; sum += w[1]; sum += w[2]; sum += w[3];
    118 			w += 4;
    119 		}
    120 		mlen += 8;
    121 		if (mlen == 0 && byte_swapped == 0)
    122 			continue;
    123 		REDUCE;
    124 		while ((mlen -= 2) >= 0) {
    125 			sum += *w++;
    126 		}
    127 		if (byte_swapped) {
    128 			REDUCE;
    129 			sum <<= 8;
    130 			byte_swapped = 0;
    131 			if (mlen == -1) {
    132 				s_util.c[1] = *(char *)w;
    133 				sum += s_util.s;
    134 				mlen = 0;
    135 			} else
    136 				mlen = -1;
    137 		} else if (mlen == -1)
    138 			s_util.c[0] = *(char *)w;
    139 	}
    140 	if (len)
    141 		printf("cksum: out of data\n");
    142 	if (mlen == -1) {
    143 		/* The last mbuf has odd # of bytes. Follow the
    144 		   standard (the odd byte may be shifted left by 8 bits
    145 		   or not as determined by endian-ness of the machine) */
    146 		s_util.c[1] = 0;
    147 		sum += s_util.s;
    148 	}
    149 	REDUCE;
    150 	return (~sum & 0xffff);
    151 }
    152