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.\" @(#)cksum.1 8.1 (Berkeley) 6/29/93
.Nd display file checksums and block counts
utility writes to the standard output three whitespace separated
fields for each input file.
These fields are a checksum
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
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 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
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 to be evaluated are considered to be the coefficients of a mod 2
polynomial M(x) of degree
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
The smallest number of octets capable of representing this integer are used.
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.
The coefficients of R(x) are considered to be a 32-bit sequence.
The bit sequence is complemented and the result is the CRC.
utility exits 0 on success, and >0 if an error occurs.
The default calculation is identical to that given in pseudo-code
.%T "Computation of Cyclic Redundancy Checks Via Table Lookup"
.%J "Communications of the \\*(tNACM\\*(sP"
utility is expected to be POSIX 1003.2 compatible.