1/*- 2 * Copyright (c) 1985, 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 * 4. 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 30#ifndef lint 31#if 0 32static char sccsid[] = "@(#)cksum.c 8.1 (Berkeley) 6/6/93"; 33#endif 34static const char rcsid[] = 35 "$FreeBSD$"; 36#endif /* not lint */ 37 38#include <sys/types.h> 39 40/* 41 * I N _ C K S U M 42 * 43 * Checksum routine for Internet Protocol family headers (C Version) 44 * 45 * There is no profit in a specialized version of the checksum 46 * function for any machine where int's are 32 bits and shorts are 16. 47 * 48 * All timed packets are smaller than 32K shorts, so there is no need to 49 * worry about carries except at the end. 50 */ 51int 52in_cksum(u_short *addr, int len) 53{ 54 register int nleft = len; 55 register u_short *w = addr; 56 register u_short answer; 57 register int sum = 0; 58 59 /* 60 * Our algorithm is simple, using a 32 bit accumulator (sum), 61 * we add sequential 16 bit words to it, and at the end, fold 62 * back all the carry bits from the top 16 bits into the lower 63 * 16 bits. 64 */ 65 while( nleft > 1 ) { 66 sum += *w++; 67 nleft -= 2; 68 } 69 70 /* mop up an odd byte, if necessary */ 71 if( nleft == 1 ) 72 sum += (*(u_char *)w) << 8; 73 74 /* 75 * add back carry outs from top 16 bits to low 16 bits 76 */ 77 sum = (sum >> 16) + (sum & 0xffff); /* add hi 16 to low 16 */ 78 sum += (sum >> 16); /* add carry */ 79 answer = ~sum; /* truncate to 16 bits */ 80 return (answer); 81} 82