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 #ifndef lint 35 static char sccsid[] = "@(#)cksum.c 5.2 (Berkeley) 5/11/93"; 36 #endif /* not lint */ 37 38 #ifdef sgi 39 #ident "$Revision: 1.1 $" 40 #endif 41 42 #include <sys/types.h> 43 44 /* 45 * I N _ C K S U M 46 * 47 * Checksum routine for Internet Protocol family headers (C Version) 48 * 49 * There is no profit in a specialized version of the checksum 50 * function for any machine where int's are 32 bits and shorts are 16. 51 * 52 * All timed packets are smaller than 32K shorts, so there is no need to 53 * worry about carries except at the end. 54 */ 55 int 56 in_cksum(u_short *addr, int len) 57 { 58 register int nleft = len; 59 register u_short *w = addr; 60 register u_short answer; 61 register int sum = 0; 62 63 /* 64 * Our algorithm is simple, using a 32 bit accumulator (sum), 65 * we add sequential 16 bit words to it, and at the end, fold 66 * back all the carry bits from the top 16 bits into the lower 67 * 16 bits. 68 */ 69 while( nleft > 1 ) { 70 sum += *w++; 71 nleft -= 2; 72 } 73 74 /* mop up an odd byte, if necessary */ 75 if( nleft == 1 ) 76 sum += (*(u_char *)w) << 8; 77 78 /* 79 * add back carry outs from top 16 bits to low 16 bits 80 */ 81 sum = (sum >> 16) + (sum & 0xffff); /* add hi 16 to low 16 */ 82 sum += (sum >> 16); /* add carry */ 83 answer = ~sum; /* truncate to 16 bits */ 84 return (answer); 85 } 86