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.\" @(#)cksum.1 5.5 (Berkeley) 6/27/91
.Nd display file checksums and block counts
utility writes to standard output three whitespace separated fields for each
input file (or the standard input by default).
These fields are a checksum
the total number of bytes in the file and
The options are as follows:
Use historic algorithms instead of the (superior) default one.
Algorithm 1 is the algorithm used by historic
algorithm and by historic
This is a 16-bit checksum, with a right rotation before each addition;
Algorithm 2 is the algorithm used by historic
This is a 32-bit checksum, and is defined as follows:
.Bd -unfilled -offset indent
r = s % 2^16 + (s % 2^32) / 2^16;
cksum = (r % 2^16) + r / 2^16;
Both algorithm 1 and 2 write to 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
Partial blocks are rounded up.
used is based on the polynomial used for
in the networking standard
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
value corresponding to a given file is defined by
.Bd -filled -offset indent
bits of the file are considered to be the coefficients of a mod 2
polynomial M(x) of degree
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.
During the division, each time the intermediate remainder is zero, it
is changed to the next value from a predefined sequence of
32-bit integers before completing the division.
This sequence is long and complex -- see the source code for more
The coefficients of R(x) are considered to be a 32-bit sequence.
The calculation used is identical to that given in pseudo-code in
article referenced below.
utility exits 0 on success, and >0 if an error occurs.
.%T "Computation of Cyclic Redundancy Checks Via Table Lookup"
.%J "Communications of the \\*(tNACM\\*(sP"
is expected to conform to
projects / unix-history / blob