1 /*- 2 * SPDX-License-Identifier: BSD-3-Clause 3 * 4 * Copyright (c) 1989, 1993 5 * The Regents of the University of California. All rights reserved. 6 * 7 * This code is derived from software contributed to Berkeley by 8 * Mike Muuss. 9 * 10 * Redistribution and use in source and binary forms, with or without 11 * modification, are permitted provided that the following conditions 12 * are met: 13 * 1. Redistributions of source code must retain the above copyright 14 * notice, this list of conditions and the following disclaimer. 15 * 2. Redistributions in binary form must reproduce the above copyright 16 * notice, this list of conditions and the following disclaimer in the 17 * documentation and/or other materials provided with the distribution. 18 * 3. Neither the name of the University nor the names of its contributors 19 * may be used to endorse or promote products derived from this software 20 * without specific prior written permission. 21 * 22 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 23 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 24 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 25 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 26 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 27 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 28 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 29 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 30 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 31 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 32 * SUCH DAMAGE. 33 */ 34 35 #include <string.h> 36 37 #include "utils.h" 38 39 /* 40 * in_cksum -- 41 * Checksum routine for Internet Protocol family headers (C Version) 42 */ 43 u_short 44 in_cksum(u_char *addr, int len) 45 { 46 int nleft, sum; 47 u_char *w; 48 union { 49 u_short us; 50 u_char uc[2]; 51 } last; 52 u_short answer; 53 54 nleft = len; 55 sum = 0; 56 w = addr; 57 58 /* 59 * Our algorithm is simple, using a 32 bit accumulator (sum), we add 60 * sequential 16 bit words to it, and at the end, fold back all the 61 * carry bits from the top 16 bits into the lower 16 bits. 62 */ 63 while (nleft > 1) { 64 u_short data; 65 66 memcpy(&data, w, sizeof(data)); 67 sum += data; 68 w += sizeof(data); 69 nleft -= sizeof(data); 70 } 71 72 /* mop up an odd byte, if necessary */ 73 if (nleft == 1) { 74 last.uc[0] = *w; 75 last.uc[1] = 0; 76 sum += last.us; 77 } 78 79 /* add back carry outs from top 16 bits to low 16 bits */ 80 sum = (sum >> 16) + (sum & 0xffff); /* add hi 16 to low 16 */ 81 sum += (sum >> 16); /* add carry */ 82 answer = ~sum; /* truncate to 16 bits */ 83 return(answer); 84 } 85