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in_cksum.c revision 1.2 
      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  *	@(#)in_cksum.c	7.3 (Berkeley) 6/28/90
     34  */
     35 
     36 #include "types.h"
     37 #include "mbuf.h"
     38 
     39 /*
     40  * Checksum routine for Internet Protocol family headers (Portable Version).
     41  *
     42  * This routine is very heavily used in the network
     43  * code and should be modified for each CPU to be as fast as possible.
     44  */
     45 
     46 #define ADDCARRY(x)  (x > 65535 ? x -= 65535 : x)
     47 #define REDUCE {l_util.l = sum; sum = l_util.s[0] + l_util.s[1]; ADDCARRY(sum);}
     48 
     49 in_cksum_c(m, len)
     50 	register struct mbuf *m;
     51 	register int len;
     52 {
     53 	register u_short *w;
     54 	register int sum = 0;
     55 	register int mlen = 0;
     56 	int byte_swapped = 0;
     57 
     58 	union {
     59 		char	c[2];
     60 		u_short	s;
     61 	} s_util;
     62 	union {
     63 		u_short s[2];
     64 		long	l;
     65 	} l_util;
     66 
     67 	for (;m && len; m = m->m_next) {
     68 		if (m->m_len == 0)
     69 			continue;
     70 		w = mtod(m, u_short *);
     71 		if (mlen == -1) {
     72 			/*
     73 			 * The first byte of this mbuf is the continuation
     74 			 * of a word spanning between this mbuf and the
     75 			 * last mbuf.
     76 			 *
     77 			 * s_util.c[0] is already saved when scanning previous
     78 			 * mbuf.
     79 			 */
     80 			s_util.c[1] = *(char *)w;
     81 			sum += s_util.s;
     82 			w = (u_short *)((char *)w + 1);
     83 			mlen = m->m_len - 1;
     84 			len--;
     85 		} else
     86 			mlen = m->m_len;
     87 		if (len < mlen)
     88 			mlen = len;
     89 		len -= mlen;
     90 		/*
     91 		 * Force to even boundary.
     92 		 */
     93 		if ((1 & (int) w) && (mlen > 0)) {
     94 			REDUCE;
     95 			sum <<= 8;
     96 			s_util.c[0] = *(u_char *)w;
     97 			w = (u_short *)((char *)w + 1);
     98 			mlen--;
     99 			byte_swapped = 1;
    100 		}
    101 		/*
    102 		 * Unroll the loop to make overhead from
    103 		 * branches &c small.
    104 		 */
    105 		while ((mlen -= 32) >= 0) {
    106 			sum += w[0]; sum += w[1]; sum += w[2]; sum += w[3];
    107 			sum += w[4]; sum += w[5]; sum += w[6]; sum += w[7];
    108 			sum += w[8]; sum += w[9]; sum += w[10]; sum += w[11];
    109 			sum += w[12]; sum += w[13]; sum += w[14]; sum += w[15];
    110 			w += 16;
    111 		}
    112 		mlen += 32;
    113 		while ((mlen -= 8) >= 0) {
    114 			sum += w[0]; sum += w[1]; sum += w[2]; sum += w[3];
    115 			w += 4;
    116 		}
    117 		mlen += 8;
    118 		if (mlen == 0 && byte_swapped == 0)
    119 			continue;
    120 		REDUCE;
    121 		while ((mlen -= 2) >= 0) {
    122 			sum += *w++;
    123 		}
    124 		if (byte_swapped) {
    125 			REDUCE;
    126 			sum <<= 8;
    127 			byte_swapped = 0;
    128 			if (mlen == -1) {
    129 				s_util.c[1] = *(char *)w;
    130 				sum += s_util.s;
    131 				mlen = 0;
    132 			} else
    133 				mlen = -1;
    134 		} else if (mlen == -1)
    135 			s_util.c[0] = *(char *)w;
    136 	}
    137 	if (len)
    138 		printf("cksum: out of data\n");
    139 	if (mlen == -1) {
    140 		/* The last mbuf has odd # of bytes. Follow the
    141 		   standard (the odd byte may be shifted left by 8 bits
    142 		   or not as determined by endian-ness of the machine) */
    143 		s_util.c[1] = 0;
    144 		sum += s_util.s;
    145 	}
    146 	REDUCE;
    147 	return (~sum & 0xffff);
    148 }
    149