1.\" Copyright (c) 1991, 1993 2.\" The Regents of the University of California. All rights reserved. 3.\" 4.\" This code is derived from software contributed to Berkeley by 5.\" the Institute of Electrical and Electronics Engineers, Inc. 6.\" 7.\" Redistribution and use in source and binary forms, with or without 8.\" modification, are permitted provided that the following conditions 9.\" are met: 10.\" 1. Redistributions of source code must retain the above copyright 11.\" notice, this list of conditions and the following disclaimer. 12.\" 2. Redistributions in binary form must reproduce the above copyright 13.\" notice, this list of conditions and the following disclaimer in the 14.\" documentation and/or other materials provided with the distribution. 15.\" 3. Neither the name of the University nor the names of its contributors 16.\" may be used to endorse or promote products derived from this software 17.\" without specific prior written permission. 18.\" 19.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 20.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 21.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 22.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 23.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 24.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 25.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 26.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 27.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 28.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 29.\" SUCH DAMAGE. 30.\" 31.\" @(#)cksum.1 8.2 (Berkeley) 4/28/95 32.\" $FreeBSD: src/usr.bin/cksum/cksum.1,v 1.19 2005/01/17 07:44:13 ru Exp $ 33.\" $DragonFly: src/usr.bin/cksum/cksum.1,v 1.4 2008/05/02 02:05:07 swildner Exp $ 34.\" 35.Dd April 28, 1995 36.Dt CKSUM 1 37.Os 38.Sh NAME 39.Nm cksum , 40.Nm sum 41.Nd display file checksums and block counts 42.Sh SYNOPSIS 43.Nm 44.Op Fl o Ar 1 | 2 | 3 45.Op Ar 46.Nm sum 47.Op Ar 48.Sh DESCRIPTION 49The 50.Nm 51utility writes to the standard output three whitespace separated 52fields for each input file. 53These fields are a checksum 54.Tn CRC , 55the total number of octets in the file and the file name. 56If no file name is specified, the standard input is used and no file name 57is written. 58.Pp 59The 60.Nm sum 61utility is identical to the 62.Nm 63utility, except that it defaults to using historic algorithm 1, as 64described below. 65It is provided for compatibility only. 66.Pp 67The options are as follows: 68.Bl -tag -width indent 69.It Fl o 70Use historic algorithms instead of the (superior) default one. 71.Pp 72Algorithm 1 is the algorithm used by historic 73.Bx 74systems as the 75.Xr sum 1 76algorithm and by historic 77.At V 78systems as the 79.Xr sum 1 80algorithm when using the 81.Fl r 82option. 83This is a 16-bit checksum, with a right rotation before each addition; 84overflow is discarded. 85.Pp 86Algorithm 2 is the algorithm used by historic 87.At V 88systems as the 89default 90.Xr sum 1 91algorithm. 92This is a 32-bit checksum, and is defined as follows: 93.Bd -unfilled -offset indent 94s = sum of all bytes; 95r = s % 2^16 + (s % 2^32) / 2^16; 96cksum = (r % 2^16) + r / 2^16; 97.Ed 98.Pp 99Algorithm 3 is what is commonly called the 100.Ql 32bit CRC 101algorithm. 102This is a 32-bit checksum. 103.Pp 104Both algorithm 1 and 2 write to the standard output the same fields as 105the default algorithm except that the size of the file in bytes is 106replaced with the size of the file in blocks. 107For historic reasons, the block size is 1024 for algorithm 1 and 512 108for algorithm 2. 109Partial blocks are rounded up. 110.El 111.Pp 112The default 113.Tn CRC 114used is based on the polynomial used for 115.Tn CRC 116error checking 117in the networking standard 118.St -iso8802-3 . 119The 120.Tn CRC 121checksum encoding is defined by the generating polynomial: 122.Bd -unfilled -offset indent 123G(x) = x^32 + x^26 + x^23 + x^22 + x^16 + x^12 + 124 x^11 + x^10 + x^8 + x^7 + x^5 + x^4 + x^2 + x + 1 125.Ed 126.Pp 127Mathematically, the 128.Tn CRC 129value corresponding to a given file is defined by 130the following procedure: 131.Bd -ragged -offset indent 132The 133.Ar n 134bits to be evaluated are considered to be the coefficients of a mod 2 135polynomial M(x) of degree 136.Ar n Ns \-1 . 137These 138.Ar n 139bits are the bits from the file, with the most significant bit being the most 140significant bit of the first octet of the file and the last bit being the least 141significant bit of the last octet, padded with zero bits (if necessary) to 142achieve an integral number of octets, followed by one or more octets 143representing the length of the file as a binary value, least significant octet 144first. 145The smallest number of octets capable of representing this integer are used. 146.Pp 147M(x) is multiplied by x^32 (i.e., shifted left 32 bits) and divided by 148G(x) using mod 2 division, producing a remainder R(x) of degree \(<= 31. 149.Pp 150The coefficients of R(x) are considered to be a 32-bit sequence. 151.Pp 152The bit sequence is complemented and the result is the CRC. 153.Ed 154.Sh EXIT STATUS 155.Ex -std cksum sum 156.Sh SEE ALSO 157.Xr md5 1 158.Pp 159The default calculation is identical to that given in pseudo-code 160in the following 161.Tn ACM 162article. 163.Rs 164.%T "Computation of Cyclic Redundancy Checks Via Table Lookup" 165.%A Dilip V. Sarwate 166.%J "Communications of the" Tn ACM 167.%D "August 1988" 168.Re 169.Sh STANDARDS 170The 171.Nm 172utility is expected to conform to 173.St -p1003.2-92 . 174.Sh HISTORY 175The 176.Nm 177utility appeared in 178.Bx 4.4 . 179