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      1 /*
      2  * Copyright (c) 1988, 1992, 1993
      3  *	The Regents of the University of California.  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. Neither the name of the University nor the names of its contributors
     14  *    may be used to endorse or promote products derived from this software
     15  *    without specific prior written permission.
     16  *
     17  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
     18  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
     19  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
     20  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
     21  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
     22  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
     23  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
     24  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
     25  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
     26  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
     27  * SUCH DAMAGE.
     28  *
     29  *	@(#)in_cksum.c	8.1 (Berkeley) 6/10/93
     30  * in_cksum.c,v 1.2 1994/08/02 07:48:16 davidg Exp
     31  */
     32 
     33 #include <slirp.h>
     34 
     35 /*
     36  * Checksum routine for Internet Protocol family headers (Portable Version).
     37  *
     38  * This routine is very heavily used in the network
     39  * code and should be modified for each CPU to be as fast as possible.
     40  *
     41  * XXX Since we will never span more than 1 mbuf, we can optimise this
     42  */
     43 
     44 #define ADDCARRY(x)  (x > 65535 ? x -= 65535 : x)
     45 #define REDUCE {l_util.l = sum; sum = l_util.s[0] + l_util.s[1]; ADDCARRY(sum);}
     46 
     47 int cksum(struct mbuf *m, int len)
     48 {
     49 	register u_int16_t *w;
     50 	register int sum = 0;
     51 	register int mlen = 0;
     52 	int byte_swapped = 0;
     53 
     54 	union {
     55 		u_int8_t	c[2];
     56 		u_int16_t	s;
     57 	} s_util;
     58 	union {
     59 		u_int16_t s[2];
     60 		u_int32_t l;
     61 	} l_util;
     62 
     63 	if (m->m_len == 0)
     64 	   goto cont;
     65 	w = mtod(m, u_int16_t *);
     66 
     67 	mlen = m->m_len;
     68 
     69 	if (len < mlen)
     70 	   mlen = len;
     71 	len -= mlen;
     72 	/*
     73 	 * Force to even boundary.
     74 	 */
     75 	if ((1 & (long) w) && (mlen > 0)) {
     76 		REDUCE;
     77 		sum <<= 8;
     78 		s_util.c[0] = *(u_int8_t *)w;
     79 		w = (u_int16_t *)((int8_t *)w + 1);
     80 		mlen--;
     81 		byte_swapped = 1;
     82 	}
     83 	/*
     84 	 * Unroll the loop to make overhead from
     85 	 * branches &c small.
     86 	 */
     87 	while ((mlen -= 32) >= 0) {
     88 		sum += w[0]; sum += w[1]; sum += w[2]; sum += w[3];
     89 		sum += w[4]; sum += w[5]; sum += w[6]; sum += w[7];
     90 		sum += w[8]; sum += w[9]; sum += w[10]; sum += w[11];
     91 		sum += w[12]; sum += w[13]; sum += w[14]; sum += w[15];
     92 		w += 16;
     93 	}
     94 	mlen += 32;
     95 	while ((mlen -= 8) >= 0) {
     96 		sum += w[0]; sum += w[1]; sum += w[2]; sum += w[3];
     97 		w += 4;
     98 	}
     99 	mlen += 8;
    100 	if (mlen == 0 && byte_swapped == 0)
    101 	   goto cont;
    102 	REDUCE;
    103 	while ((mlen -= 2) >= 0) {
    104 		sum += *w++;
    105 	}
    106 
    107 	if (byte_swapped) {
    108 		REDUCE;
    109 		sum <<= 8;
    110 		byte_swapped = 0;
    111 		if (mlen == -1) {
    112 			s_util.c[1] = *(u_int8_t *)w;
    113 			sum += s_util.s;
    114 			mlen = 0;
    115 		} else
    116 
    117 		   mlen = -1;
    118 	} else if (mlen == -1)
    119 	   s_util.c[0] = *(u_int8_t *)w;
    120 
    121 cont:
    122 #ifdef DEBUG
    123 	if (len) {
    124 		DEBUG_ERROR((dfd, "cksum: out of data\n"));
    125 		DEBUG_ERROR((dfd, " len = %d\n", len));
    126 	}
    127 #endif
    128 	if (mlen == -1) {
    129 		/* The last mbuf has odd # of bytes. Follow the
    130 		 standard (the odd byte may be shifted left by 8 bits
    131 			   or not as determined by endian-ness of the machine) */
    132 		s_util.c[1] = 0;
    133 		sum += s_util.s;
    134 	}
    135 	REDUCE;
    136 	return (~sum & 0xffff);
    137 }
    138