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in_cksum.c revision 1.18 
      1 /*	$NetBSD: in_cksum.c,v 1.18 2005/02/03 03:49:01 perry 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. Neither the name of the University nor the names of its contributors
     16  *    may be used to endorse or promote products derived from this software
     17  *    without specific prior written permission.
     18  *
     19  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
     20  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
     21  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
     22  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
     23  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
     24  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
     25  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
     26  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
     27  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
     28  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
     29  * SUCH DAMAGE.
     30  *
     31  *	@(#)in_cksum.c	8.1 (Berkeley) 6/10/93
     32  */
     33 
     34 #include <sys/cdefs.h>
     35 __KERNEL_RCSID(0, "$NetBSD: in_cksum.c,v 1.18 2005/02/03 03:49:01 perry Exp $");
     36 
     37 #include <sys/param.h>
     38 #include <sys/mbuf.h>
     39 #include <sys/systm.h>
     40 #include <netinet/in.h>
     41 
     42 /*
     43  * Checksum routine for Internet Protocol family headers (Portable Version).
     44  *
     45  * This routine is very heavily used in the network
     46  * code and should be modified for each CPU to be as fast as possible.
     47  */
     48 
     49 #define ADDCARRY(x)  (x > 65535 ? x -= 65535 : x)
     50 #define REDUCE {l_util.l = sum; sum = l_util.s[0] + l_util.s[1]; ADDCARRY(sum);}
     51 
     52 int
     53 in_cksum(struct mbuf *m, int len)
     54 {
     55 	u_int16_t *w;
     56 	int sum = 0;
     57 	int mlen = 0;
     58 	int byte_swapped = 0;
     59 
     60 	union {
     61 		u_int8_t  c[2];
     62 		u_int16_t s;
     63 	} s_util;
     64 	union {
     65 		u_int16_t s[2];
     66 		u_int32_t l;
     67 	} l_util;
     68 
     69 	for (;m && len; m = m->m_next) {
     70 		if (m->m_len == 0)
     71 			continue;
     72 		w = mtod(m, u_int16_t *);
     73 		if (mlen == -1) {
     74 			/*
     75 			 * The first byte of this mbuf is the continuation
     76 			 * of a word spanning between this mbuf and the
     77 			 * last mbuf.
     78 			 *
     79 			 * s_util.c[0] is already saved when scanning previous
     80 			 * mbuf.
     81 			 */
     82 			s_util.c[1] = *(u_int8_t *)w;
     83 			sum += s_util.s;
     84 			w = (u_int16_t *)((u_int8_t *)w + 1);
     85 			mlen = m->m_len - 1;
     86 			len--;
     87 		} else
     88 			mlen = m->m_len;
     89 		if (len < mlen)
     90 			mlen = len;
     91 		len -= mlen;
     92 		/*
     93 		 * Force to even boundary.
     94 		 */
     95 		if ((1 & (long) w) && (mlen > 0)) {
     96 			REDUCE;
     97 			sum <<= 8;
     98 			s_util.c[0] = *(u_int8_t *)w;
     99 			w = (u_int16_t *)((int8_t *)w + 1);
    100 			mlen--;
    101 			byte_swapped = 1;
    102 		}
    103 		/*
    104 		 * Unroll the loop to make overhead from
    105 		 * branches &c small.
    106 		 */
    107 		while ((mlen -= 32) >= 0) {
    108 			sum += w[0]; sum += w[1]; sum += w[2]; sum += w[3];
    109 			sum += w[4]; sum += w[5]; sum += w[6]; sum += w[7];
    110 			sum += w[8]; sum += w[9]; sum += w[10]; sum += w[11];
    111 			sum += w[12]; sum += w[13]; sum += w[14]; sum += w[15];
    112 			w += 16;
    113 		}
    114 		mlen += 32;
    115 		while ((mlen -= 8) >= 0) {
    116 			sum += w[0]; sum += w[1]; sum += w[2]; sum += w[3];
    117 			w += 4;
    118 		}
    119 		mlen += 8;
    120 		if (mlen == 0 && byte_swapped == 0)
    121 			continue;
    122 		REDUCE;
    123 		while ((mlen -= 2) >= 0) {
    124 			sum += *w++;
    125 		}
    126 		if (byte_swapped) {
    127 			REDUCE;
    128 			sum <<= 8;
    129 			byte_swapped = 0;
    130 			if (mlen == -1) {
    131 				s_util.c[1] = *(u_int8_t *)w;
    132 				sum += s_util.s;
    133 				mlen = 0;
    134 			} else
    135 				mlen = -1;
    136 		} else if (mlen == -1)
    137 			s_util.c[0] = *(u_int8_t *)w;
    138 	}
    139 	if (len)
    140 		printf("cksum: out of data\n");
    141 	if (mlen == -1) {
    142 		/* The last mbuf has odd # of bytes. Follow the
    143 		   standard (the odd byte may be shifted left by 8 bits
    144 		   or not as determined by endian-ness of the machine) */
    145 		s_util.c[1] = 0;
    146 		sum += s_util.s;
    147 	}
    148 	REDUCE;
    149 	return (~sum & 0xffff);
    150 }
    151