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31 .\" @(#)cksum.1 8.2 (Berkeley) 4/28/95
32 .\" $FreeBSD: src/usr.bin/cksum/cksum.1,v 1.19 2005/01/17 07:44:13 ru Exp $
33 .\" $DragonFly: src/usr.bin/cksum/cksum.1,v 1.4 2008/05/02 02:05:07 swildner Exp $
41 .Nd display file checksums and block counts
51 utility writes to the standard output three whitespace separated
52 fields for each input file.
53 These fields are a checksum
55 the total number of octets in the file and the file name.
56 If no file name is specified, the standard input is used and no file name
61 utility is identical to the
63 utility, except that it defaults to using historic algorithm 1, as
65 It is provided for compatibility only.
67 The options are as follows:
68 .Bl -tag -width indent
70 Use historic algorithms instead of the (superior) default one.
72 Algorithm 1 is the algorithm used by historic
76 algorithm and by historic
80 algorithm when using the
83 This is a 16-bit checksum, with a right rotation before each addition;
84 overflow is discarded.
86 Algorithm 2 is the algorithm used by historic
92 This is a 32-bit checksum, and is defined as follows:
93 .Bd -unfilled -offset indent
95 r = s % 2^16 + (s % 2^32) / 2^16;
96 cksum = (r % 2^16) + r / 2^16;
99 Algorithm 3 is what is commonly called the
102 This is a 32-bit checksum.
104 Both algorithm 1 and 2 write to the standard output the same fields as
105 the default algorithm except that the size of the file in bytes is
106 replaced with the size of the file in blocks.
107 For historic reasons, the block size is 1024 for algorithm 1 and 512
109 Partial blocks are rounded up.
114 used is based on the polynomial used for
117 in the networking standard
121 checksum encoding is defined by the generating polynomial:
122 .Bd -unfilled -offset indent
123 G(x) = x^32 + x^26 + x^23 + x^22 + x^16 + x^12 +
124 x^11 + x^10 + x^8 + x^7 + x^5 + x^4 + x^2 + x + 1
129 value corresponding to a given file is defined by
130 the following procedure:
131 .Bd -ragged -offset indent
134 bits to be evaluated are considered to be the coefficients of a mod 2
135 polynomial M(x) of degree
139 bits are the bits from the file, with the most significant bit being the most
140 significant bit of the first octet of the file and the last bit being the least
141 significant bit of the last octet, padded with zero bits (if necessary) to
142 achieve an integral number of octets, followed by one or more octets
143 representing the length of the file as a binary value, least significant octet
145 The smallest number of octets capable of representing this integer are used.
147 M(x) is multiplied by x^32 (i.e., shifted left 32 bits) and divided by
148 G(x) using mod 2 division, producing a remainder R(x) of degree \(<= 31.
150 The coefficients of R(x) are considered to be a 32-bit sequence.
152 The bit sequence is complemented and the result is the CRC.
159 The default calculation is identical to that given in pseudo-code
164 .%T "Computation of Cyclic Redundancy Checks Via Table Lookup"
166 .%J "Communications of the" Tn ACM
172 utility is expected to conform to