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Diffstat (limited to 'file_cmds/cksum/cksum.1')
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diff --git a/file_cmds/cksum/cksum.1 b/file_cmds/cksum/cksum.1 new file mode 100644 index 0000000..b4161fe --- /dev/null +++ b/file_cmds/cksum/cksum.1 @@ -0,0 +1,182 @@ +.\" 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 . |