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 8.1 (Berkeley) 6/29/93 36.\" $Id: cksum.1,v 1.2 1997/04/27 08:45:43 jmg Exp $ 37.\" 38.Dd June 29, 1993 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 46.Op Fl o Op \&1 \&| \&2 47.Op Ar file ... 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 options are as follows: 60.Bl -tag -width indent 61.It Fl o 62Use historic algorithms instead of the (superior) default one. 63.Pp 64Algorithm 1 is the algorithm used by historic 65.Bx 66systems as the 67.Xr sum 1 68algorithm and by historic 69.At V 70systems as the 71.Xr sum 72algorithm when using the 73.Fl r 74option. 75This is a 16-bit checksum, with a right rotation before each addition; 76overflow is discarded. 77.Pp 78Algorithm 2 is the algorithm used by historic 79.At V 80systems as the 81default 82.Xr sum 83algorithm. 84This is a 32-bit checksum, and is defined as follows: 85.Bd -unfilled -offset indent 86s = sum of all bytes; 87r = s % 2^16 + (s % 2^32) / 2^16; 88cksum = (r % 2^16) + r / 2^16; 89.Ed 90.Pp 91Both algorithm 1 and 2 write to the standard output the same fields as 92the default algorithm except that the size of the file in bytes is 93replaced with the size of the file in blocks. 94For historic reasons, the block size is 1024 for algorithm 1 and 512 95for algorithm 2. 96Partial blocks are rounded up. 97.El 98.Pp 99The default 100.Tn CRC 101used is based on the polynomial used for 102.Tn CRC 103error checking 104in the networking standard 105.St -iso8802-3 106The 107.Tn CRC 108checksum encoding is defined by the generating polynomial: 109.Pp 110.Bd -unfilled -offset indent 111G(x) = x^32 + x^26 + x^23 + x^22 + x^16 + x^12 + 112 x^11 + x^10 + x^8 + x^7 + x^5 + x^4 + x^2 + x + 1 113.Ed 114.Pp 115Mathematically, the 116.Tn CRC 117value corresponding to a given file is defined by 118the following procedure: 119.Bd -filled -offset indent 120The 121.Ar n 122bits to be evaluated are considered to be the coefficients of a mod 2 123polynomial M(x) of degree 124.Ar n Ns \-1 . 125These 126.Ar n 127bits are the bits from the file, with the most significant bit being the most 128significant bit of the first octet of the file and the last bit being the least 129significant bit of the last octet, padded with zero bits (if necessary) to 130achieve an integral number of octets, followed by one or more octets 131representing the length of the file as a binary value, least significant octet 132first. 133The smallest number of octets capable of representing this integer are used. 134.Pp 135M(x) is multiplied by x^32 (i.e., shifted left 32 bits) and divided by 136G(x) using mod 2 division, producing a remainder R(x) of degree <= 31. 137.Pp 138The coefficients of R(x) are considered to be a 32-bit sequence. 139.Pp 140The bit sequence is complemented and the result is the CRC. 141.Ed 142.Pp 143The 144.Nm 145utility exits 0 on success, and >0 if an error occurs. 146.Sh SEE ALSO 147.Xr md5 1 148.Rs 149The default calculation is identical to that given in pseudo-code 150in the following 151.Tn ACM 152article. 153.Rs 154.%T "Computation of Cyclic Redundancy Checks Via Table Lookup" 155.%A Dilip V. Sarwate 156.%J "Communications of the \\*(tNACM\\*(sP" 157.%D "August 1988" 158.Re 159.Sh STANDARDS 160The 161.Nm 162utility is expected to be POSIX 1003.2 compatible. 163.Sh HISTORY 164The 165.Nm 166utility appeared in 167.Bx 4.4 . 168