1.\" Copyright (c) 1991, 1991 The Regents of the University of California. 2.\" 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 5.5 (Berkeley) 6/27/91 36.\" 37.Dd June 27, 1991 38.Dt CKSUM 1 39.Os 40.Sh NAME 41.Nm cksum 42.Nd display file checksums and block counts 43.Sh SYNOPSIS 44.Nm cksum 45.Op Fl o Op \&1 \&| \&2 46.Op Ar file ... 47.Sh DESCRIPTION 48The 49.Nm cksum 50utility writes to standard output three whitespace separated fields for each 51input file (or the standard input by default). 52These fields are a checksum 53.Tn CRC , 54the total number of bytes in the file and 55the file name. 56.Pp 57The options are as follows: 58.Bl -tag -width indent 59.It Fl o 60Use historic algorithms instead of the (superior) default one. 61.Pp 62Algorithm 1 is the algorithm used by historic 63.Bx 64systems as the 65.Xr sum 1 66algorithm and by historic 67.At V 68systems as the 69.Xr sum 70algorithm when using the 71.Fl r 72option. 73This is a 16-bit checksum, with a right rotation before each addition; 74overflow is discarded. 75.Pp 76Algorithm 2 is the algorithm used by historic 77.At V 78systems as the 79default 80.Xr sum 81algorithm. 82This is a 32-bit checksum, and is defined as follows: 83.Bd -unfilled -offset indent 84s = sum of all bytes; 85r = s % 2^16 + (s % 2^32) / 2^16; 86cksum = (r % 2^16) + r / 2^16; 87.Ed 88.Pp 89Both algorithm 1 and 2 write to standard output the same fields as 90the default algorithm except that the size of the file in bytes is 91replaced with the size of the file in blocks. 92For historic reasons, the block size is 1024 for algorithm 1 and 512 93for algorithm 2. 94Partial blocks are rounded up. 95.El 96.Pp 97The default 98.Tn CRC 99used is based on the polynomial used for 100.Tn CRC 101error checking 102in the networking standard 103.St -iso8802-3 104The 105.Tn CRC 106checksum encoding is defined by the generating polynomial: 107.Pp 108.Bd -unfilled -offset indent 109G(x) = x^32 + x^26 + x^23 + x^22 + x^16 + x^12 + 110 x^11 + x^10 + x^8 + x^7 + x^5 + x^4 + x^2 + x + 1 111.Ed 112.Pp 113Mathematically, the 114.Tn CRC 115value corresponding to a given file is defined by 116the following procedure: 117.Bd -filled -offset indent 118The 119.Ar n 120bits of the file are considered to be the coefficients of a mod 2 121polynomial M(x) of degree 122.Ar n Ns \-1 . 123.Pp 124M(x) is multiplied by x^32 (i.e., shifted left 32 bits) and divided by 125G(x) using mod 2 division, producing a remainder R(x) of degree <= 31. 126During the division, each time the intermediate remainder is zero, it 127is changed to the next value from a predefined sequence of 12832-bit integers before completing the division. 129This sequence is long and complex -- see the source code for more 130information. 131.Pp 132The coefficients of R(x) are considered to be a 32-bit sequence. 133.Ed 134.Pp 135The calculation used is identical to that given in pseudo-code in 136the 137.Tn ACM 138article referenced below. 139.Pp 140The 141.Nm cksum 142utility exits 0 on success, and >0 if an error occurs. 143.Sh SEE ALSO 144.Rs 145.%T "Computation of Cyclic Redundancy Checks Via Table Lookup" 146.%A Dilip V. Sarwate 147.%J "Communications of the \\*(tNACM\\*(sP" 148.%D "August 1988" 149.Re 150.Sh STANDARDS 151.Nm Cksum 152is expected to conform to 153.St -p1003.2 . 154.Sh HISTORY 155The 156.Nm cksum 157utility is 158.Ud . 159