182 lines
5.4 KiB
Groff
182 lines
5.4 KiB
Groff
.\" 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
|
|
.\" $FreeBSD$
|
|
.\"
|
|
.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:
|
|
.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 .
|