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