[apple/file_cmds.git] / cksum / cksum.1

.\" 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 .
Commit	Line	Data
864a4b6e A	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 8.2 (Berkeley) 4/28/95
	36	.\" $FreeBSD: src/usr.bin/cksum/cksum.1,v 1.19 2005/01/17 07:44:13 ru Exp $
	37	.\"
	38	.Dd April 28, 1995
	39	.Dt CKSUM 1
	40	.Os
	41	.Sh NAME
	42	.Nm cksum ,
	43	.Nm sum
	44	.Nd display file checksums and block counts
	45	.Sh SYNOPSIS
	46	.Nm
	47	.Op Fl o Ar 1 \| 2 \| 3
	48	.Op Ar
	49	.Nm sum
	50	.Op Ar
	51	.Sh DESCRIPTION
	52	The
	53	.Nm
	54	utility writes to the standard output three whitespace separated
	55	fields for each input file.
	56	These fields are a checksum
	57	.Tn CRC ,
	58	the total number of octets in the file and the file name.
	59	If no file name is specified, the standard input is used and no file name
	60	is written.
	61	.Pp
	62	The
	63	.Nm sum
	64	utility is identical to the
65	.Nm
66	utility, except that it defaults to using historic algorithm 1, as
67	described below.
68	It is provided for compatibility only.
69	.Pp
70	The options are as follows:
71	.Bl -tag -width indent
72	.It Fl o
73	Use historic algorithms instead of the (superior) default one.
74	.Pp
75	Algorithm 1 is the algorithm used by historic
76	.Bx
77	systems as the
78	.Xr sum 1
79	algorithm and by historic
80	.At V
81	systems as the
82	.Xr sum 1
83	algorithm when using the
84	.Fl r
85	option.
86	This is a 16-bit checksum, with a right rotation before each addition;
87	overflow is discarded.
88	.Pp
89	Algorithm 2 is the algorithm used by historic
90	.At V
91	systems as the
92	default
93	.Xr sum 1
94	algorithm.
95	This is a 32-bit checksum, and is defined as follows:
96	.Bd -unfilled -offset indent
97	s = sum of all bytes;
98	r = s % 2^16 + (s % 2^32) / 2^16;
99	cksum = (r % 2^16) + r / 2^16;
100	.Ed
101	.Pp
102	Algorithm 3 is what is commonly called the
103	.Ql 32bit CRC
104	algorithm.
105	This is a 32-bit checksum.
106	.Pp
107	Both algorithm 1 and 2 write to the standard output the same fields as
108	the default algorithm except that the size of the file in bytes is
109	replaced with the size of the file in blocks.
110	For historic reasons, the block size is 1024 for algorithm 1 and 512
111	for algorithm 2.
112	Partial blocks are rounded up.
113	.El
114	.Pp
115	The default
116	.Tn CRC
117	used is based on the polynomial used for
118	.Tn CRC
119	error checking
120	in the networking standard
121	.St -iso8802-3 .
122	The
123	.Tn CRC
124	checksum encoding is defined by the generating polynomial:
125	.Pp
126	.Bd -unfilled -offset indent
127	G(x) = x^32 + x^26 + x^23 + x^22 + x^16 + x^12 +
128	x^11 + x^10 + x^8 + x^7 + x^5 + x^4 + x^2 + x + 1
129	.Ed
130	.Pp
131	Mathematically, the
132	.Tn CRC
133	value corresponding to a given file is defined by
134	the following procedure:
135	.Bd -ragged -offset indent
136	The
137	.Ar n
138	bits to be evaluated are considered to be the coefficients of a mod 2
139	polynomial M(x) of degree
140	.Ar n Ns \-1 .
141	These
142	.Ar n
143	bits are the bits from the file, with the most significant bit being the most
144	significant bit of the first octet of the file and the last bit being the least
145	significant bit of the last octet, padded with zero bits (if necessary) to
146	achieve an integral number of octets, followed by one or more octets
147	representing the length of the file as a binary value, least significant octet
148	first.
149	The smallest number of octets capable of representing this integer are used.
150	.Pp
151	M(x) is multiplied by x^32 (i.e., shifted left 32 bits) and divided by
152	G(x) using mod 2 division, producing a remainder R(x) of degree <= 31.
153	.Pp
154	The coefficients of R(x) are considered to be a 32-bit sequence.
155	.Pp
156	The bit sequence is complemented and the result is the CRC.
157	.Ed
158	.Sh EXIT STATUS
159	.Ex -std cksum sum
160	.Sh SEE ALSO
161	.Xr md5 1
162	.Pp
163	The default calculation is identical to that given in pseudo-code
164	in the following
165	.Tn ACM
166	article.
167	.Rs
168	.%T "Computation of Cyclic Redundancy Checks Via Table Lookup"
169	.%A Dilip V. Sarwate
170	.%J "Communications of the" Tn ACM
171	.%D "August 1988"
172	.Re
173	.Sh STANDARDS
174	The
175	.Nm
176	utility is expected to conform to
177	.St -p1003.2-92 .
178	.Sh HISTORY
179	The
180	.Nm
181	utility appeared in
182	.Bx 4.4 .