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.\" $FreeBSD$ 33.\" 34.Dd April 28, 1995 35.Dt CKSUM 1 36.Os 37.Sh NAME 38.Nm cksum , 39.Nm sum 40.Nd display file checksums and block counts 41.Sh SYNOPSIS 42.Nm 43.Op Fl o Ar 1 | 2 | 3 44.Op Ar 45.Nm sum 46.Op Ar 47.Sh DESCRIPTION 48The 49.Nm 50utility writes to the standard output three whitespace separated 51fields for each input file. 52These fields are a checksum 53.Tn CRC , 54the total number of octets in the file and the file name. 55If no file name is specified, the standard input is used and no file name 56is written. 57.Pp 58The 59.Nm sum 60utility is identical to the 61.Nm 62utility, except that it defaults to using historic algorithm 1, as 63described below. 64It is provided for compatibility only. 65.Pp 66The options are as follows: 67.Bl -tag -width indent 68.It Fl o 69Use historic algorithms instead of the (superior) default one. 70.Pp 71Algorithm 1 is the algorithm used by historic 72.Bx 73systems as the 74.Xr sum 1 75algorithm and by historic 76.At V 77systems as the 78.Xr sum 1 79algorithm when using the 80.Fl r 81option. 82This is a 16-bit checksum, with a right rotation before each addition; 83overflow is discarded. 84.Pp 85Algorithm 2 is the algorithm used by historic 86.At V 87systems as the 88default 89.Xr sum 1 90algorithm. 91This is a 32-bit checksum, and is defined as follows: 92.Bd -unfilled -offset indent 93s = sum of all bytes; 94r = s % 2^16 + (s % 2^32) / 2^16; 95cksum = (r % 2^16) + r / 2^16; 96.Ed 97.Pp 98Algorithm 3 is what is commonly called the 99.Ql 32bit CRC 100algorithm. 101This is a 32-bit checksum. 102.Pp 103Both algorithm 1 and 2 write to the standard output the same fields as 104the default algorithm except that the size of the file in bytes is 105replaced with the size of the file in blocks. 106For historic reasons, the block size is 1024 for algorithm 1 and 512 107for algorithm 2. 108Partial blocks are rounded up. 109.El 110.Pp 111The default 112.Tn CRC 113used is based on the polynomial used for 114.Tn CRC 115error checking 116in the networking standard 117.St -iso8802-3 . 118The 119.Tn CRC 120checksum encoding is defined by the generating polynomial: 121.Bd -unfilled -offset indent 122G(x) = x^32 + x^26 + x^23 + x^22 + x^16 + x^12 + 123 x^11 + x^10 + x^8 + x^7 + x^5 + x^4 + x^2 + x + 1 124.Ed 125.Pp 126Mathematically, the 127.Tn CRC 128value corresponding to a given file is defined by 129the following procedure: 130.Bd -ragged -offset indent 131The 132.Ar n 133bits to be evaluated are considered to be the coefficients of a mod 2 134polynomial M(x) of degree 135.Ar n Ns \-1 . 136These 137.Ar n 138bits are the bits from the file, with the most significant bit being the most 139significant bit of the first octet of the file and the last bit being the least 140significant bit of the last octet, padded with zero bits (if necessary) to 141achieve an integral number of octets, followed by one or more octets 142representing the length of the file as a binary value, least significant octet 143first. 144The smallest number of octets capable of representing this integer are used. 145.Pp 146M(x) is multiplied by x^32 (i.e., shifted left 32 bits) and divided by 147G(x) using mod 2 division, producing a remainder R(x) of degree <= 31. 148.Pp 149The coefficients of R(x) are considered to be a 32-bit sequence. 150.Pp 151The bit sequence is complemented and the result is the CRC. 152.Ed 153.Sh EXIT STATUS 154.Ex -std cksum sum 155.Sh SEE ALSO 156.Xr md5 1 157.Pp 158The default calculation is identical to that given in pseudo-code 159in the following 160.Tn ACM 161article. 162.Rs 163.%T "Computation of Cyclic Redundancy Checks Via Table Lookup" 164.%A Dilip V. Sarwate 165.%J "Communications of the" Tn ACM 166.%D "August 1988" 167.Re 168.Sh STANDARDS 169The 170.Nm 171utility is expected to conform to 172.St -p1003.2-92 . 173.Sh HISTORY 174The 175.Nm 176utility appeared in 177.Bx 4.4 . 178