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35 .\" @(#)cksum.1 8.2 (Berkeley) 4/28/95
36 .\" $Id: cksum.1,v 1.6 1997/09/26 08:02:17 phk Exp $
43 .Nd display file checksums and block counts
60 utility writes to the standard output three whitespace separated
61 fields for each input file.
62 These fields are a checksum
64 the total number of octets in the file and the file name.
65 If no file name is specified, the standard input is used and no file name
70 utility is identical to the
72 utility, except that it defaults to using historic algorithm 1, as
74 It is provided for compatibility only.
76 The options are as follows:
77 .Bl -tag -width indent
79 Use historic algorithms instead of the (superior) default one.
81 Algorithm 1 is the algorithm used by historic
85 algorithm and by historic
89 algorithm when using the
92 This is a 16-bit checksum, with a right rotation before each addition;
93 overflow is discarded.
95 Algorithm 2 is the algorithm used by historic
101 This is a 32-bit checksum, and is defined as follows:
102 .Bd -unfilled -offset indent
103 s = sum of all bytes;
104 r = s % 2^16 + (s % 2^32) / 2^16;
105 cksum = (r % 2^16) + r / 2^16;
108 Algorithm 3 is what is commonly called the
111 This is a 32-bit checksum.
113 Both algorithm 1 and 2 write to the standard output the same fields as
114 the default algorithm except that the size of the file in bytes is
115 replaced with the size of the file in blocks.
116 For historic reasons, the block size is 1024 for algorithm 1 and 512
118 Partial blocks are rounded up.
123 used is based on the polynomial used for
126 in the networking standard
130 checksum encoding is defined by the generating polynomial:
132 .Bd -unfilled -offset indent
133 G(x) = x^32 + x^26 + x^23 + x^22 + x^16 + x^12 +
134 x^11 + x^10 + x^8 + x^7 + x^5 + x^4 + x^2 + x + 1
139 value corresponding to a given file is defined by
140 the following procedure:
141 .Bd -filled -offset indent
144 bits to be evaluated are considered to be the coefficients of a mod 2
145 polynomial M(x) of degree
149 bits are the bits from the file, with the most significant bit being the most
150 significant bit of the first octet of the file and the last bit being the least
151 significant bit of the last octet, padded with zero bits (if necessary) to
152 achieve an integral number of octets, followed by one or more octets
153 representing the length of the file as a binary value, least significant octet
155 The smallest number of octets capable of representing this integer are used.
157 M(x) is multiplied by x^32 (i.e., shifted left 32 bits) and divided by
158 G(x) using mod 2 division, producing a remainder R(x) of degree <= 31.
160 The coefficients of R(x) are considered to be a 32-bit sequence.
162 The bit sequence is complemented and the result is the CRC.
169 utilities exit 0 on success, and >0 if an error occurs.
173 The default calculation is identical to that given in pseudo-code
178 .%T "Computation of Cyclic Redundancy Checks Via Table Lookup"
180 .%J "Communications of the \\*(tNACM\\*(sP"
186 utility is expected to conform to