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in_cksum.c revision 1.13 
      1 /*	$NetBSD: in_cksum.c,v 1.13 1996/10/13 02:03:03 christos 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 #include <sys/systm.h>
     41 #include <netinet/in.h>
     42 
     43 /*
     44  * Checksum routine for Internet Protocol family headers (Portable Version).
     45  *
     46  * This routine is very heavily used in the network
     47  * code and should be modified for each CPU to be as fast as possible.
     48  */
     49 
     50 #define ADDCARRY(x)  (x > 65535 ? x -= 65535 : x)
     51 #define REDUCE {l_util.l = sum; sum = l_util.s[0] + l_util.s[1]; ADDCARRY(sum);}
     52 
     53 int
     54 in_cksum(m, len)
     55 	register struct mbuf *m;
     56 	register int len;
     57 {
     58 	register u_int16_t *w;
     59 	register int sum = 0;
     60 	register int mlen = 0;
     61 	int byte_swapped = 0;
     62 
     63 	union {
     64 		u_int8_t  c[2];
     65 		u_int16_t s;
     66 	} s_util;
     67 	union {
     68 		u_int16_t s[2];
     69 		u_int32_t l;
     70 	} l_util;
     71 
     72 	for (;m && len; m = m->m_next) {
     73 		if (m->m_len == 0)
     74 			continue;
     75 		w = mtod(m, u_int16_t *);
     76 		if (mlen == -1) {
     77 			/*
     78 			 * The first byte of this mbuf is the continuation
     79 			 * of a word spanning between this mbuf and the
     80 			 * last mbuf.
     81 			 *
     82 			 * s_util.c[0] is already saved when scanning previous
     83 			 * mbuf.
     84 			 */
     85 			s_util.c[1] = *(u_int8_t *)w;
     86 			sum += s_util.s;
     87 			w = (u_int16_t *)((u_int8_t *)w + 1);
     88 			mlen = m->m_len - 1;
     89 			len--;
     90 		} else
     91 			mlen = m->m_len;
     92 		if (len < mlen)
     93 			mlen = len;
     94 		len -= mlen;
     95 		/*
     96 		 * Force to even boundary.
     97 		 */
     98 		if ((1 & (long) w) && (mlen > 0)) {
     99 			REDUCE;
    100 			sum <<= 8;
    101 			s_util.c[0] = *(u_int8_t *)w;
    102 			w = (u_int16_t *)((int8_t *)w + 1);
    103 			mlen--;
    104 			byte_swapped = 1;
    105 		}
    106 		/*
    107 		 * Unroll the loop to make overhead from
    108 		 * branches &c small.
    109 		 */
    110 		while ((mlen -= 32) >= 0) {
    111 			sum += w[0]; sum += w[1]; sum += w[2]; sum += w[3];
    112 			sum += w[4]; sum += w[5]; sum += w[6]; sum += w[7];
    113 			sum += w[8]; sum += w[9]; sum += w[10]; sum += w[11];
    114 			sum += w[12]; sum += w[13]; sum += w[14]; sum += w[15];
    115 			w += 16;
    116 		}
    117 		mlen += 32;
    118 		while ((mlen -= 8) >= 0) {
    119 			sum += w[0]; sum += w[1]; sum += w[2]; sum += w[3];
    120 			w += 4;
    121 		}
    122 		mlen += 8;
    123 		if (mlen == 0 && byte_swapped == 0)
    124 			continue;
    125 		REDUCE;
    126 		while ((mlen -= 2) >= 0) {
    127 			sum += *w++;
    128 		}
    129 		if (byte_swapped) {
    130 			REDUCE;
    131 			sum <<= 8;
    132 			byte_swapped = 0;
    133 			if (mlen == -1) {
    134 				s_util.c[1] = *(u_int8_t *)w;
    135 				sum += s_util.s;
    136 				mlen = 0;
    137 			} else
    138 				mlen = -1;
    139 		} else if (mlen == -1)
    140 			s_util.c[0] = *(u_int8_t *)w;
    141 	}
    142 	if (len)
    143 		printf("cksum: out of data\n");
    144 	if (mlen == -1) {
    145 		/* The last mbuf has odd # of bytes. Follow the
    146 		   standard (the odd byte may be shifted left by 8 bits
    147 		   or not as determined by endian-ness of the machine) */
    148 		s_util.c[1] = 0;
    149 		sum += s_util.s;
    150 	}
    151 	REDUCE;
    152 	return (~sum & 0xffff);
    153 }
    154