.\" Copyright (c) 1991, 1993 .\" The Regents of the University of California. All rights reserved. .\" .\" This code is derived from software contributed to Berkeley by .\" the Institute of Electrical and Electronics Engineers, Inc. .\" .\" Redistribution and use in source and binary forms, with or without .\" modification, are permitted provided that the following conditions .\" are met: .\" 1. Redistributions of source code must retain the above copyright .\" notice, this list of conditions and the following disclaimer. .\" 2. Redistributions in binary form must reproduce the above copyright .\" notice, this list of conditions and the following disclaimer in the .\" documentation and/or other materials provided with the distribution. .\" 3. All advertising materials mentioning features or use of this software .\" must display the following acknowledgement: .\" This product includes software developed by the University of .\" California, Berkeley and its contributors. .\" 4. Neither the name of the University nor the names of its contributors .\" may be used to endorse or promote products derived from this software .\" without specific prior written permission. .\" .\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND .\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE .\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE .\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE .\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL .\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS .\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) .\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT .\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY .\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF .\" SUCH DAMAGE. .\" .\" @(#)cksum.1 8.2 (Berkeley) 4/28/95 .\" $FreeBSD: src/usr.bin/cksum/cksum.1,v 1.19 2005/01/17 07:44:13 ru Exp $ .\" .Dd April 28, 1995 .Dt CKSUM 1 .Os .Sh NAME .Nm cksum , .Nm sum .Nd display file checksums and block counts .Sh SYNOPSIS .Nm .Op Fl o Ar 1 | 2 | 3 .Op Ar .Nm sum .Op Ar .Sh DESCRIPTION The .Nm utility writes to the standard output three whitespace separated fields for each input file. These fields are a checksum .Tn CRC , the total number of octets in the file and the file name. If no file name is specified, the standard input is used and no file name is written. .Pp The .Nm sum utility is identical to the .Nm utility, except that it defaults to using historic algorithm 1, as described below. It is provided for compatibility only. .Pp The options are as follows: .Bl -tag -width indent .It Fl o Use historic algorithms instead of the (superior) default one. .Pp Algorithm 1 is the algorithm used by historic .Bx systems as the .Xr sum 1 algorithm and by historic .At V systems as the .Xr sum 1 algorithm when using the .Fl r option. This is a 16-bit checksum, with a right rotation before each addition; overflow is discarded. .Pp Algorithm 2 is the algorithm used by historic .At V systems as the default .Xr sum 1 algorithm. This is a 32-bit checksum, and is defined as follows: .Bd -unfilled -offset indent s = sum of all bytes; r = s % 2^16 + (s % 2^32) / 2^16; cksum = (r % 2^16) + r / 2^16; .Ed .Pp Algorithm 3 is what is commonly called the .Ql 32bit CRC algorithm. This is a 32-bit checksum. .Pp Both algorithm 1 and 2 write to the standard output the same fields as the default algorithm except that the size of the file in bytes is replaced with the size of the file in blocks. For historic reasons, the block size is 1024 for algorithm 1 and 512 for algorithm 2. Partial blocks are rounded up. .El .Pp The default .Tn CRC used is based on the polynomial used for .Tn CRC error checking in the networking standard .St -iso8802-3 . The .Tn CRC checksum encoding is defined by the generating polynomial: .Pp .Bd -unfilled -offset indent G(x) = x^32 + x^26 + x^23 + x^22 + x^16 + x^12 + x^11 + x^10 + x^8 + x^7 + x^5 + x^4 + x^2 + x + 1 .Ed .Pp Mathematically, the .Tn CRC value corresponding to a given file is defined by the following procedure: .Bd -ragged -offset indent The .Ar n bits to be evaluated are considered to be the coefficients of a mod 2 polynomial M(x) of degree .Ar n Ns \-1 . These .Ar n bits are the bits from the file, with the most significant bit being the most significant bit of the first octet of the file and the last bit being the least significant bit of the last octet, padded with zero bits (if necessary) to achieve an integral number of octets, followed by one or more octets representing the length of the file as a binary value, least significant octet first. The smallest number of octets capable of representing this integer are used. .Pp M(x) is multiplied by x^32 (i.e., shifted left 32 bits) and divided by G(x) using mod 2 division, producing a remainder R(x) of degree <= 31. .Pp The coefficients of R(x) are considered to be a 32-bit sequence. .Pp The bit sequence is complemented and the result is the CRC. .Ed .Sh EXIT STATUS .Ex -std cksum sum .Sh SEE ALSO .Xr md5 1 .Pp The default calculation is identical to that given in pseudo-code in the following .Tn ACM article. .Rs .%T "Computation of Cyclic Redundancy Checks Via Table Lookup" .%A Dilip V. Sarwate .%J "Communications of the" Tn ACM .%D "August 1988" .Re .Sh STANDARDS The .Nm utility is expected to conform to .St -p1003.2-92 . .Sh HISTORY The .Nm utility appeared in .Bx 4.4 .