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.\" $FreeBSD$ 37.\" 38.Dd April 28, 1995 39.Dt CKSUM 1 40.Os 41.Sh NAME 42.Nm cksum , 43.Nm sum 44.Nd display file checksums and block counts 45.Sh SYNOPSIS 46.Nm 47.Op Fl o Ar 1 | 2 | 3 48.Op Ar 49.Nm sum 50.Op Ar 51.Sh DESCRIPTION 52The 53.Nm 54utility writes to the standard output three whitespace separated 55fields for each input file. 56These fields are a checksum 57.Tn CRC , 58the total number of octets in the file and the file name. 59If no file name is specified, the standard input is used and no file name 60is written. 61.Pp 62The 63.Nm sum 64utility is identical to the 65.Nm 66utility, except that it defaults to using historic algorithm 1, as 67described below. 68It is provided for compatibility only. 69.Pp 70The options are as follows: 71.Bl -tag -width indent 72.It Fl o 73Use historic algorithms instead of the (superior) default one. 74.Pp 75Algorithm 1 is the algorithm used by historic 76.Bx 77systems as the 78.Xr sum 1 79algorithm and by historic 80.At V 81systems as the 82.Xr sum 1 83algorithm when using the 84.Fl r 85option. 86This is a 16-bit checksum, with a right rotation before each addition; 87overflow is discarded. 88.Pp 89Algorithm 2 is the algorithm used by historic 90.At V 91systems as the 92default 93.Xr sum 1 94algorithm. 95This is a 32-bit checksum, and is defined as follows: 96.Bd -unfilled -offset indent 97s = sum of all bytes; 98r = s % 2^16 + (s % 2^32) / 2^16; 99cksum = (r % 2^16) + r / 2^16; 100.Ed 101.Pp 102Algorithm 3 is what is commonly called the 103.Ql 32bit CRC 104algorithm. 105This is a 32-bit checksum. 106.Pp 107Both algorithm 1 and 2 write to the standard output the same fields as 108the default algorithm except that the size of the file in bytes is 109replaced with the size of the file in blocks. 110For historic reasons, the block size is 1024 for algorithm 1 and 512 111for algorithm 2. 112Partial blocks are rounded up. 113.El 114.Pp 115The default 116.Tn CRC 117used is based on the polynomial used for 118.Tn CRC 119error checking 120in the networking standard 121.St -iso8802-3 . 122The 123.Tn CRC 124checksum encoding is defined by the generating polynomial: 125.Pp 126.Bd -unfilled -offset indent 127G(x) = x^32 + x^26 + x^23 + x^22 + x^16 + x^12 + 128 x^11 + x^10 + x^8 + x^7 + x^5 + x^4 + x^2 + x + 1 129.Ed 130.Pp 131Mathematically, the 132.Tn CRC 133value corresponding to a given file is defined by 134the following procedure: 135.Bd -ragged -offset indent 136The 137.Ar n 138bits to be evaluated are considered to be the coefficients of a mod 2 139polynomial M(x) of degree 140.Ar n Ns \-1 . 141These 142.Ar n 143bits are the bits from the file, with the most significant bit being the most 144significant bit of the first octet of the file and the last bit being the least 145significant bit of the last octet, padded with zero bits (if necessary) to 146achieve an integral number of octets, followed by one or more octets 147representing the length of the file as a binary value, least significant octet 148first. 149The smallest number of octets capable of representing this integer are used. 150.Pp 151M(x) is multiplied by x^32 (i.e., shifted left 32 bits) and divided by 152G(x) using mod 2 division, producing a remainder R(x) of degree <= 31. 153.Pp 154The coefficients of R(x) are considered to be a 32-bit sequence. 155.Pp 156The bit sequence is complemented and the result is the CRC. 157.Ed 158.Sh EXIT STATUS 159.Ex -std cksum sum 160.Sh SEE ALSO 161.Xr md5 1 162.Pp 163The default calculation is identical to that given in pseudo-code 164in the following 165.Tn ACM 166article. 167.Rs 168.%T "Computation of Cyclic Redundancy Checks Via Table Lookup" 169.%A Dilip V. Sarwate 170.%J "Communications of the" Tn ACM 171.%D "August 1988" 172.Re 173.Sh STANDARDS 174The 175.Nm 176utility is expected to conform to 177.St -p1003.2-92 . 178.Sh HISTORY 179The 180.Nm 181utility appeared in 182.Bx 4.4 . 183