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.\" $Id: cksum.1,v 1.4 1997/06/25 07:02:00 charnier Exp $ 37.\" 38.Dd April 28, 1995 39.Dt CKSUM 1 40.Os BSD 4.4 41.Sh NAME 42.Nm cksum 43.Nd display file checksums and block counts 44.Sh SYNOPSIS 45.Nm cksum 46.Op Fl o Ar \&1 No \&| Ar \&2 47.Op Ar file ... 48.Nm sum 49.Op Ar file ... 50.Sh DESCRIPTION 51The 52.Nm cksum 53utility writes to the standard output three whitespace separated 54fields for each input file. 55These fields are a checksum 56.Tn CRC , 57the total number of octets in the file and the file name. 58If no file name is specified, the standard input is used and no file name 59is written. 60.Pp 61The 62.Nm sum 63utility is identical to the 64.Nm cksum 65utility, except that it defaults to using historic algorithm 1, as 66described below. 67It is provided for compatibility only. 68.Pp 69The options are as follows: 70.Bl -tag -width indent 71.It Fl o 72Use historic algorithms instead of the (superior) default one. 73.Pp 74Algorithm 1 is the algorithm used by historic 75.Bx 76systems as the 77.Xr sum 1 78algorithm and by historic 79.At V 80systems as the 81.Xr sum 82algorithm when using the 83.Fl r 84option. 85This is a 16-bit checksum, with a right rotation before each addition; 86overflow is discarded. 87.Pp 88Algorithm 2 is the algorithm used by historic 89.At V 90systems as the 91default 92.Xr sum 93algorithm. 94This is a 32-bit checksum, and is defined as follows: 95.Bd -unfilled -offset indent 96s = sum of all bytes; 97r = s % 2^16 + (s % 2^32) / 2^16; 98cksum = (r % 2^16) + r / 2^16; 99.Ed 100.Pp 101Both algorithm 1 and 2 write to the standard output the same fields as 102the default algorithm except that the size of the file in bytes is 103replaced with the size of the file in blocks. 104For historic reasons, the block size is 1024 for algorithm 1 and 512 105for algorithm 2. 106Partial blocks are rounded up. 107.El 108.Pp 109The default 110.Tn CRC 111used is based on the polynomial used for 112.Tn CRC 113error checking 114in the networking standard 115.St -iso8802-3 116The 117.Tn CRC 118checksum encoding is defined by the generating polynomial: 119.Pp 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 -filled -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.Pp 153The 154.Nm cksum 155and 156.Nm sum 157utilities exit 0 on success, and >0 if an error occurs. 158.Sh SEE ALSO 159.Xr md5 1 160.Rs 161The default calculation is identical to that given in pseudo-code 162in the following 163.Tn ACM 164article. 165.Rs 166.%T "Computation of Cyclic Redundancy Checks Via Table Lookup" 167.%A Dilip V. Sarwate 168.%J "Communications of the \\*(tNACM\\*(sP" 169.%D "August 1988" 170.Re 171.Sh STANDARDS 172The 173.Nm cksum 174utility is expected to conform to 175.St -p1003.2-92 . 176.Sh HISTORY 177The 178.Nm cksum 179utility appeared in 180.Bx 4.4 . 181