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. 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 #include <sys/cdefs.h> 31 #ifndef lint 32 #if 0 33 static char sccsid[] = "@(#)cksum.c 5.2 (Berkeley) 5/11/93"; 34 #else 35 __RCSID("$NetBSD: cksum.c,v 1.7 2007/05/17 00:36:31 christos Exp $"); 36 #endif 37 #endif /* not lint */ 38 39 #include <sys/types.h> 40 #include "globals.h" 41 42 /* 43 * I N _ C K S U M 44 * 45 * Checksum routine for Internet Protocol family headers (C Version) 46 * 47 * There is no profit in a specialized version of the checksum 48 * function for any machine where int's are 32 bits and shorts are 16. 49 * 50 * All timed packets are smaller than 32K shorts, so there is no need to 51 * worry about carries except at the end. 52 */ 53 int 54 in_cksum(const void *data, int len) 55 { 56 const u_char *addr = data; 57 int nleft = len; 58 uint16_t answer; 59 int sum = 0; 60 61 /* 62 * Our algorithm is simple, using a 32 bit accumulator (sum), 63 * we add sequential 16 bit words to it, and at the end, fold 64 * back all the carry bits from the top 16 bits into the lower 65 * 16 bits. 66 */ 67 while (nleft > 1) { 68 uint16_t w; 69 70 memcpy(&w, addr, sizeof(w)); 71 sum += w; 72 addr += 2; 73 nleft -= 2; 74 } 75 76 /* mop up an odd byte, if necessary */ 77 if (nleft == 1) 78 sum += *addr << 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