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%sccs.include.redist.man%
@(#)cksum.1 5.2 (Berkeley) 04/04/91
cksum [-o [1 | 2]] [file ...]
The options are as follows:
-o Use historic algorithms instead of the (superior) default one.
Algorithm 1 is the algorithm used by historic BSD systems as the sum (1) algorithm and by historic System V systems as the sum algorithm when using the -r option. This is a 16-bit checksum, with a right rotation before each addition; overflow is discarded. Algorithm 2 is the algorithm used by historic System V systems as the default sum algorithm. This is a 32-bit checksum, and is defined as follows:s = sum of all bytes; 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 for algorithm 2. Partial blocks are rounded up.
The default CRC used is based on the polynomial used for CRC error checking in the networking standard ISO 8802-3: 1989. The CRC checksum encoding is defined by the generating polynomial:
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
Mathematically, the CRC value corresponding to a given file is defined by the following procedure:
The n bits of the file are considered to be the coefficients of a mod 2 polynomial M(x) of degree n -1.
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 information.
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 the ACM article referenced below.
The cksum utility exits 0 on success, and >0 if an error occurs.