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in_cksum.c revision 1.5 
      1 /*
      2  * Copyright (c) 1988 Regents of the University of California.
      3  * All rights reserved.
      4  *
      5  * Redistribution and use in source and binary forms, with or without
      6  * modification, are permitted provided that the following conditions
      7  * are met:
      8  * 1. Redistributions of source code must retain the above copyright
      9  *    notice, this list of conditions and the following disclaimer.
     10  * 2. Redistributions in binary form must reproduce the above copyright
     11  *    notice, this list of conditions and the following disclaimer in the
     12  *    documentation and/or other materials provided with the distribution.
     13  * 3. All advertising materials mentioning features or use of this software
     14  *    must display the following acknowledgement:
     15  *	This product includes software developed by the University of
     16  *	California, Berkeley and its contributors.
     17  * 4. Neither the name of the University nor the names of its contributors
     18  *    may be used to endorse or promote products derived from this software
     19  *    without specific prior written permission.
     20  *
     21  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
     22  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
     23  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
     24  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
     25  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
     26  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
     27  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
     28  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
     29  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
     30  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
     31  * SUCH DAMAGE.
     32  *
     33  *	from: @(#)in_cksum.c	7.3 (Berkeley) 6/28/90
     34  *	$Id: in_cksum.c,v 1.5 1994/01/08 21:21:39 mycroft Exp $
     35  */
     36 
     37 #include <sys/types.h>
     38 #include <sys/mbuf.h>
     39 
     40 /*
     41  * Checksum routine for Internet Protocol family headers (Portable Version).
     42  *
     43  * This routine is very heavily used in the network
     44  * code and should be modified for each CPU to be as fast as possible.
     45  */
     46 
     47 #define	ADDCARRY(x) (x > 65535 ? x -= 65535 : x)
     48 #define	REDUCE {l_util.l = sum; sum = l_util.s[0] + l_util.s[1]; ADDCARRY(sum);}
     49 
     50 in_cksum_c(m, len)
     51 	register struct mbuf *m;
     52 	register int len;
     53 {
     54 	register u_short *w;
     55 	register int sum = 0;
     56 	register int mlen = 0;
     57 	int byte_swapped = 0;
     58 
     59 	union {
     60 		char	c[2];
     61 		u_short	s;
     62 	} s_util;
     63 	union {
     64 		u_short s[2];
     65 		long	l;
     66 	} l_util;
     67 
     68 	for (;m && len; m = m->m_next) {
     69 		if (m->m_len == 0)
     70 			continue;
     71 		w = mtod(m, u_short *);
     72 		if (mlen == -1) {
     73 			/*
     74 			 * The first byte of this mbuf is the continuation
     75 			 * of a word spanning between this mbuf and the
     76 			 * last mbuf.
     77 			 *
     78 			 * s_util.c[0] is already saved when scanning previous
     79 			 * mbuf.
     80 			 */
     81 			s_util.c[1] = *(char *)w;
     82 			sum += s_util.s;
     83 			w = (u_short *)((char *)w + 1);
     84 			mlen = m->m_len - 1;
     85 			len--;
     86 		} else
     87 			mlen = m->m_len;
     88 		if (len < mlen)
     89 			mlen = len;
     90 		len -= mlen;
     91 		/*
     92 		 * Force to even boundary.
     93 		 */
     94 		if ((1 & (int) w) && (mlen > 0)) {
     95 			REDUCE;
     96 			sum <<= 8;
     97 			s_util.c[0] = *(u_char *)w;
     98 			w = (u_short *)((char *)w + 1);
     99 			mlen--;
    100 			byte_swapped = 1;
    101 		}
    102 		/*
    103 		 * Unroll the loop to make overhead from
    104 		 * branches &c small.
    105 		 */
    106 		while ((mlen -= 32) >= 0) {
    107 			sum += w[0]; sum += w[1]; sum += w[2]; sum += w[3];
    108 			sum += w[4]; sum += w[5]; sum += w[6]; sum += w[7];
    109 			sum += w[8]; sum += w[9]; sum += w[10]; sum += w[11];
    110 			sum += w[12]; sum += w[13]; sum += w[14]; sum += w[15];
    111 			w += 16;
    112 		}
    113 		mlen += 32;
    114 		while ((mlen -= 8) >= 0) {
    115 			sum += w[0]; sum += w[1]; sum += w[2]; sum += w[3];
    116 			w += 4;
    117 		}
    118 		mlen += 8;
    119 		if (mlen == 0 && byte_swapped == 0)
    120 			continue;
    121 		REDUCE;
    122 		while ((mlen -= 2) >= 0) {
    123 			sum += *w++;
    124 		}
    125 		if (byte_swapped) {
    126 			REDUCE;
    127 			sum <<= 8;
    128 			byte_swapped = 0;
    129 			if (mlen == -1) {
    130 				s_util.c[1] = *(char *)w;
    131 				sum += s_util.s;
    132 				mlen = 0;
    133 			} else
    134 				mlen = -1;
    135 		} else if (mlen == -1)
    136 			s_util.c[0] = *(char *)w;
    137 	}
    138 	if (len)
    139 		printf("cksum: out of data\n");
    140 	if (mlen == -1) {
    141 		/* The last mbuf has odd # of bytes. Follow the
    142 		   standard (the odd byte may be shifted left by 8 bits
    143 		   or not as determined by endian-ness of the machine) */
    144 		s_util.c[1] = 0;
    145 		sum += s_util.s;
    146 	}
    147 	REDUCE;
    148 	return (~sum & 0xffff);
    149 }
    150