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 1.2 1997/10/17 14:19:20 lukem Exp $"); 40 #endif 41 #endif /* not lint */ 42 43 #ifdef sgi 44 #ident "$Revision: 1.2 $" 45 #endif 46 47 #include <sys/types.h> 48 #include "globals.h" 49 50 /* 51 * I N _ C K S U M 52 * 53 * Checksum routine for Internet Protocol family headers (C Version) 54 * 55 * There is no profit in a specialized version of the checksum 56 * function for any machine where int's are 32 bits and shorts are 16. 57 * 58 * All timed packets are smaller than 32K shorts, so there is no need to 59 * worry about carries except at the end. 60 */ 61 int 62 in_cksum(u_short *addr, int len) 63 { 64 register int nleft = len; 65 register u_short *w = addr; 66 register u_short answer; 67 register int sum = 0; 68 69 /* 70 * Our algorithm is simple, using a 32 bit accumulator (sum), 71 * we add sequential 16 bit words to it, and at the end, fold 72 * back all the carry bits from the top 16 bits into the lower 73 * 16 bits. 74 */ 75 while( nleft > 1 ) { 76 sum += *w++; 77 nleft -= 2; 78 } 79 80 /* mop up an odd byte, if necessary */ 81 if( nleft == 1 ) 82 sum += (*(u_char *)w) << 8; 83 84 /* 85 * add back carry outs from top 16 bits to low 16 bits 86 */ 87 sum = (sum >> 16) + (sum & 0xffff); /* add hi 16 to low 16 */ 88 sum += (sum >> 16); /* add carry */ 89 answer = ~sum; /* truncate to 16 bits */ 90 return (answer); 91 } 92