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. All advertising materials mentioning features or use of this software 16.\" must display the following acknowledgement: 17.\" This product includes software developed by the University of 18.\" California, Berkeley and its contributors. 19.\" 4. Neither the name of the University nor the names of its contributors 20.\" may be used to endorse or promote products derived from this software 21.\" without specific prior written permission. 22.\" 23.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 24.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 25.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 26.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 27.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 28.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 29.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 30.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 31.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 32.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 33.\" SUCH DAMAGE. 34.\" 35.\" @(#)cksum.1 8.2 (Berkeley) 4/28/95 36.\" $FreeBSD: src/usr.bin/cksum/cksum.1,v 1.10.2.7 2001/08/16 13:16:43 ru Exp $ 37.\" $DragonFly: src/usr.bin/cksum/cksum.1,v 1.3 2006/02/28 02:25:11 swildner Exp $ 38.\" 39.Dd April 28, 1995 40.Dt CKSUM 1 41.Os 42.Sh NAME 43.Nm cksum , 44.Nm sum 45.Nd display file checksums and block counts 46.Sh SYNOPSIS 47.Nm 48.Op Fl o Ar 1 | 2 | 3 49.Op Ar 50.Nm sum 51.Op Ar 52.Sh DESCRIPTION 53The 54.Nm 55utility writes to the standard output three whitespace separated 56fields for each input file. 57These fields are a checksum 58.Tn CRC , 59the total number of octets in the file and the file name. 60If no file name is specified, the standard input is used and no file name 61is written. 62.Pp 63The 64.Nm sum 65utility is identical to the 66.Nm 67utility, except that it defaults to using historic algorithm 1, as 68described below. 69It is provided for compatibility only. 70.Pp 71The options are as follows: 72.Bl -tag -width indent 73.It Fl o 74Use historic algorithms instead of the (superior) default one. 75.Pp 76Algorithm 1 is the algorithm used by historic 77.Bx 78systems as the 79.Xr sum 1 80algorithm and by historic 81.At V 82systems as the 83.Xr sum 1 84algorithm when using the 85.Fl r 86option. 87This is a 16-bit checksum, with a right rotation before each addition; 88overflow is discarded. 89.Pp 90Algorithm 2 is the algorithm used by historic 91.At V 92systems as the 93default 94.Xr sum 1 95algorithm. 96This is a 32-bit checksum, and is defined as follows: 97.Bd -unfilled -offset indent 98s = sum of all bytes; 99r = s % 2^16 + (s % 2^32) / 2^16; 100cksum = (r % 2^16) + r / 2^16; 101.Ed 102.Pp 103Algorithm 3 is what is commonly called the 104.Ql 32bit CRC 105algorithm. 106This is a 32-bit checksum. 107.Pp 108Both algorithm 1 and 2 write to the standard output the same fields as 109the default algorithm except that the size of the file in bytes is 110replaced with the size of the file in blocks. 111For historic reasons, the block size is 1024 for algorithm 1 and 512 112for algorithm 2. 113Partial blocks are rounded up. 114.El 115.Pp 116The default 117.Tn CRC 118used is based on the polynomial used for 119.Tn CRC 120error checking 121in the networking standard 122.St -iso8802-3 . 123The 124.Tn CRC 125checksum encoding is defined by the generating polynomial: 126.Pp 127.Bd -unfilled -offset indent 128G(x) = x^32 + x^26 + x^23 + x^22 + x^16 + x^12 + 129 x^11 + x^10 + x^8 + x^7 + x^5 + x^4 + x^2 + x + 1 130.Ed 131.Pp 132Mathematically, the 133.Tn CRC 134value corresponding to a given file is defined by 135the following procedure: 136.Bd -ragged -offset indent 137The 138.Ar n 139bits to be evaluated are considered to be the coefficients of a mod 2 140polynomial M(x) of degree 141.Ar n Ns \-1 . 142These 143.Ar n 144bits are the bits from the file, with the most significant bit being the most 145significant bit of the first octet of the file and the last bit being the least 146significant bit of the last octet, padded with zero bits (if necessary) to 147achieve an integral number of octets, followed by one or more octets 148representing the length of the file as a binary value, least significant octet 149first. 150The smallest number of octets capable of representing this integer are used. 151.Pp 152M(x) is multiplied by x^32 (i.e., shifted left 32 bits) and divided by 153G(x) using mod 2 division, producing a remainder R(x) of degree \(<= 31. 154.Pp 155The coefficients of R(x) are considered to be a 32-bit sequence. 156.Pp 157The bit sequence is complemented and the result is the CRC. 158.Ed 159.Sh DIAGNOSTICS 160.Ex -std cksum sum 161.Sh SEE ALSO 162.Xr md5 1 163.Pp 164The default calculation is identical to that given in pseudo-code 165in the following 166.Tn ACM 167article. 168.Rs 169.%T "Computation of Cyclic Redundancy Checks Via Table Lookup" 170.%A Dilip V. Sarwate 171.%J "Communications of the" Tn ACM 172.%D "August 1988" 173.Re 174.Sh STANDARDS 175The 176.Nm 177utility is expected to conform to 178.St -p1003.2-92 . 179.Sh HISTORY 180The 181.Nm 182utility appeared in 183.Bx 4.4 . 184