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35 .\" @(#)cksum.1 8.2 (Berkeley) 4/28/95
36 .\" $FreeBSD: src/usr.bin/cksum/cksum.1,v 1.10.2.7 2001/08/16 13:16:43 ru Exp $
37 .\" $DragonFly: src/usr.bin/cksum/cksum.1,v 1.3 2006/02/28 02:25:11 swildner Exp $
45 .Nd display file checksums and block counts
55 utility writes to the standard output three whitespace separated
56 fields for each input file.
57 These fields are a checksum
59 the total number of octets in the file and the file name.
60 If no file name is specified, the standard input is used and no file name
65 utility is identical to the
67 utility, except that it defaults to using historic algorithm 1, as
69 It is provided for compatibility only.
71 The options are as follows:
72 .Bl -tag -width indent
74 Use historic algorithms instead of the (superior) default one.
76 Algorithm 1 is the algorithm used by historic
80 algorithm and by historic
84 algorithm when using the
87 This is a 16-bit checksum, with a right rotation before each addition;
88 overflow is discarded.
90 Algorithm 2 is the algorithm used by historic
96 This is a 32-bit checksum, and is defined as follows:
97 .Bd -unfilled -offset indent
99 r = s % 2^16 + (s % 2^32) / 2^16;
100 cksum = (r % 2^16) + r / 2^16;
103 Algorithm 3 is what is commonly called the
106 This is a 32-bit checksum.
108 Both algorithm 1 and 2 write to the standard output the same fields as
109 the default algorithm except that the size of the file in bytes is
110 replaced with the size of the file in blocks.
111 For historic reasons, the block size is 1024 for algorithm 1 and 512
113 Partial blocks are rounded up.
118 used is based on the polynomial used for
121 in the networking standard
125 checksum encoding is defined by the generating polynomial:
127 .Bd -unfilled -offset indent
128 G(x) = x^32 + x^26 + x^23 + x^22 + x^16 + x^12 +
129 x^11 + x^10 + x^8 + x^7 + x^5 + x^4 + x^2 + x + 1
134 value corresponding to a given file is defined by
135 the following procedure:
136 .Bd -ragged -offset indent
139 bits to be evaluated are considered to be the coefficients of a mod 2
140 polynomial M(x) of degree
144 bits are the bits from the file, with the most significant bit being the most
145 significant bit of the first octet of the file and the last bit being the least
146 significant bit of the last octet, padded with zero bits (if necessary) to
147 achieve an integral number of octets, followed by one or more octets
148 representing the length of the file as a binary value, least significant octet
150 The smallest number of octets capable of representing this integer are used.
152 M(x) is multiplied by x^32 (i.e., shifted left 32 bits) and divided by
153 G(x) using mod 2 division, producing a remainder R(x) of degree \(<= 31.
155 The coefficients of R(x) are considered to be a 32-bit sequence.
157 The bit sequence is complemented and the result is the CRC.
164 The default calculation is identical to that given in pseudo-code
169 .%T "Computation of Cyclic Redundancy Checks Via Table Lookup"
171 .%J "Communications of the" Tn ACM
177 utility is expected to conform to