11553Srgrimes/*- 21553Srgrimes * Copyright (c) 1985, 1993 31553Srgrimes * The Regents of the University of California. All rights reserved. 41553Srgrimes * 51553Srgrimes * Redistribution and use in source and binary forms, with or without 61553Srgrimes * modification, are permitted provided that the following conditions 71553Srgrimes * are met: 81553Srgrimes * 1. Redistributions of source code must retain the above copyright 91553Srgrimes * notice, this list of conditions and the following disclaimer. 101553Srgrimes * 2. Redistributions in binary form must reproduce the above copyright 111553Srgrimes * notice, this list of conditions and the following disclaimer in the 121553Srgrimes * documentation and/or other materials provided with the distribution. 131553Srgrimes * 4. Neither the name of the University nor the names of its contributors 141553Srgrimes * may be used to endorse or promote products derived from this software 151553Srgrimes * without specific prior written permission. 161553Srgrimes * 171553Srgrimes * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 181553Srgrimes * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 191553Srgrimes * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 201553Srgrimes * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 211553Srgrimes * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 221553Srgrimes * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 231553Srgrimes * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 241553Srgrimes * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 251553Srgrimes * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 261553Srgrimes * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 271553Srgrimes * SUCH DAMAGE. 281553Srgrimes */ 291553Srgrimes 301553Srgrimes#ifndef lint 3130642Scharnier#if 0 321553Srgrimesstatic char sccsid[] = "@(#)cksum.c 8.1 (Berkeley) 6/6/93"; 3330642Scharnier#endif 3430642Scharnierstatic const char rcsid[] = 3550479Speter "$FreeBSD$"; 361553Srgrimes#endif /* not lint */ 371553Srgrimes 381553Srgrimes#include <sys/types.h> 391553Srgrimes 401553Srgrimes/* 411553Srgrimes * I N _ C K S U M 421553Srgrimes * 431553Srgrimes * Checksum routine for Internet Protocol family headers (C Version) 441553Srgrimes * 451553Srgrimes * There is no profit in a specialized version of the checksum 461553Srgrimes * function for any machine where int's are 32 bits and shorts are 16. 471553Srgrimes * 481553Srgrimes * All timed packets are smaller than 32K shorts, so there is no need to 491553Srgrimes * worry about carries except at the end. 501553Srgrimes */ 511553Srgrimesint 52246209Scharnierin_cksum(u_short *addr, int len) 531553Srgrimes{ 541553Srgrimes register int nleft = len; 551553Srgrimes register u_short *w = addr; 561553Srgrimes register u_short answer; 571553Srgrimes register int sum = 0; 581553Srgrimes 591553Srgrimes /* 601553Srgrimes * Our algorithm is simple, using a 32 bit accumulator (sum), 611553Srgrimes * we add sequential 16 bit words to it, and at the end, fold 621553Srgrimes * back all the carry bits from the top 16 bits into the lower 631553Srgrimes * 16 bits. 641553Srgrimes */ 651553Srgrimes while( nleft > 1 ) { 661553Srgrimes sum += *w++; 671553Srgrimes nleft -= 2; 681553Srgrimes } 691553Srgrimes 701553Srgrimes /* mop up an odd byte, if necessary */ 711553Srgrimes if( nleft == 1 ) 721553Srgrimes sum += (*(u_char *)w) << 8; 731553Srgrimes 741553Srgrimes /* 751553Srgrimes * add back carry outs from top 16 bits to low 16 bits 761553Srgrimes */ 771553Srgrimes sum = (sum >> 16) + (sum & 0xffff); /* add hi 16 to low 16 */ 781553Srgrimes sum += (sum >> 16); /* add carry */ 791553Srgrimes answer = ~sum; /* truncate to 16 bits */ 801553Srgrimes return (answer); 811553Srgrimes} 82