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.\" 37.Dd June 29, 1993 38.Dt CKSUM 1 39.Os BSD 4.4 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 the standard output three whitespace separated 51fields for each input file. 52These fields are a checksum 53.Tn CRC , 54the total number of octets in the file and the file name. 55If no file name is specified, the standard input is used and no file name 56is written. 57.Pp 58The options are as follows: 59.Bl -tag -width indent 60.It Fl o 61Use historic algorithms instead of the (superior) default one. 62.Pp 63Algorithm 1 is the algorithm used by historic 64.Bx 65systems as the 66.Xr sum 1 67algorithm and by historic 68.At V 69systems as the 70.Xr sum 71algorithm when using the 72.Fl r 73option. 74This is a 16-bit checksum, with a right rotation before each addition; 75overflow is discarded. 76.Pp 77Algorithm 2 is the algorithm used by historic 78.At V 79systems as the 80default 81.Xr sum 82algorithm. 83This is a 32-bit checksum, and is defined as follows: 84.Bd -unfilled -offset indent 85s = sum of all bytes; 86r = s % 2^16 + (s % 2^32) / 2^16; 87cksum = (r % 2^16) + r / 2^16; 88.Ed 89.Pp 90Both algorithm 1 and 2 write to the standard output the same fields as 91the default algorithm except that the size of the file in bytes is 92replaced with the size of the file in blocks. 93For historic reasons, the block size is 1024 for algorithm 1 and 512 94for algorithm 2. 95Partial blocks are rounded up. 96.El 97.Pp 98The default 99.Tn CRC 100used is based on the polynomial used for 101.Tn CRC 102error checking 103in the networking standard 104.St -iso8802-3 105The 106.Tn CRC 107checksum encoding is defined by the generating polynomial: 108.Pp 109.Bd -unfilled -offset indent 110G(x) = x^32 + x^26 + x^23 + x^22 + x^16 + x^12 + 111 x^11 + x^10 + x^8 + x^7 + x^5 + x^4 + x^2 + x + 1 112.Ed 113.Pp 114Mathematically, the 115.Tn CRC 116value corresponding to a given file is defined by 117the following procedure: 118.Bd -filled -offset indent 119The 120.Ar n 121bits to be evaluated are considered to be the coefficients of a mod 2 122polynomial M(x) of degree 123.Ar n Ns \-1 . 124These 125.Ar n 126bits are the bits from the file, with the most significant bit being the most 127significant bit of the first octet of the file and the last bit being the least 128significant bit of the last octet, padded with zero bits (if necessary) to 129achieve an integral number of octets, followed by one or more octets 130representing the length of the file as a binary value, least significant octet 131first. 132The smallest number of octets capable of representing this integer are used. 133.Pp 134M(x) is multiplied by x^32 (i.e., shifted left 32 bits) and divided by 135G(x) using mod 2 division, producing a remainder R(x) of degree <= 31. 136.Pp 137The coefficients of R(x) are considered to be a 32-bit sequence. 138.Pp 139The bit sequence is complemented and the result is the CRC. 140.Ed 141.Pp 142The 143.Nm cksum 144utility exits 0 on success, and >0 if an error occurs. 145.Sh SEE ALSO 146The default calculation is identical to that given in pseudo-code 147in the following 148.Tn ACM 149article. 150.Rs 151.%T "Computation of Cyclic Redundancy Checks Via Table Lookup" 152.%A Dilip V. Sarwate 153.%J "Communications of the \\*(tNACM\\*(sP" 154.%D "August 1988" 155.Re 156.Sh STANDARDS 157The 158.Nm cksum 159utility is expected to be POSIX 1003.2 compatible. 160.Sh HISTORY 161The 162.Nm cksum 163utility appears in 164.Bx 4.4 . 165