1 /*- 2 * Copyright (c) 1985, 1993 The 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 34 #include <sys/cdefs.h> 35 #ifndef lint 36 #if 0 37 static char sccsid[] = "@(#)cksum.c 5.2 (Berkeley) 5/11/93"; 38 #else 39 __RCSID("$NetBSD: cksum.c,v 1.3 2001/09/02 00:13:06 reinoud Exp $"); 40 #endif 41 #endif /* not lint */ 42 43 #include <sys/types.h> 44 #include "globals.h" 45 46 /* 47 * I N _ C K S U M 48 * 49 * Checksum routine for Internet Protocol family headers (C Version) 50 * 51 * There is no profit in a specialized version of the checksum 52 * function for any machine where int's are 32 bits and shorts are 16. 53 * 54 * All timed packets are smaller than 32K shorts, so there is no need to 55 * worry about carries except at the end. 56 */ 57 int 58 in_cksum(u_short *addr, int len) 59 { 60 register int nleft = len; 61 register u_short *w = addr; 62 register u_short answer; 63 register int sum = 0; 64 65 /* 66 * Our algorithm is simple, using a 32 bit accumulator (sum), 67 * we add sequential 16 bit words to it, and at the end, fold 68 * back all the carry bits from the top 16 bits into the lower 69 * 16 bits. 70 */ 71 while( nleft > 1 ) { 72 sum += *w++; 73 nleft -= 2; 74 } 75 76 /* mop up an odd byte, if necessary */ 77 if( nleft == 1 ) 78 sum += (*(u_char *)w) << 8; 79 80 /* 81 * add back carry outs from top 16 bits to low 16 bits 82 */ 83 sum = (sum >> 16) + (sum & 0xffff); /* add hi 16 to low 16 */ 84 sum += (sum >> 16); /* add carry */ 85 answer = ~sum; /* truncate to 16 bits */ 86 return (answer); 87 } 88