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I am looking for the range of possible values that could be returned by cksum. E.g.

echo -n '/my/path/filename' | cksum | cut -d' ' -f1

returns 2379496500. What is the range (min and max) of the possible values that can be returned?

BTW, the parameter above is the string value of a fully qualified file path, not the contents of the file specified thereby.

amphibient
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1 Answers1

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The POSIX standard specifies the CRC algorithm used by cksum. I quote the relevant part here (emphasis mine):

The encoding for the CRC checksum is defined by the generating polynomial:

G(x)=x32+x26+x23+x22+x16+x12+x11+x10+x8+x7+x5+x4+x2+x+1

Mathematically, the CRC value corresponding to a given file shall be defined by the following procedure:

The n bits to be evaluated are considered to be the coefficients of a mod 2 polynomial M(x) of degree n-1. These n 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 first. The smallest number of octets capable of representing this integer shall be used.

M(x) is multiplied by x32 (that is, 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.

So there you go, the CRC of cksum is a 32-bit sequence, so it ranges in value from 0 to 232-1 = 4294967295 (thank you Google!)

Joseph R.
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