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The
**cksum**
utility writes to the standard output three whitespace separated
fields for each input file.
These fields are a checksum
* CRC*,
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
is written.

The
**sum**
utility is identical to the
**cksum**
utility, except that it defaults to using historic algorithm 1, as
described below.
It is provided for compatibility only.

The options are as follows:

| |

Use historic algorithms instead of the (superior) default one.
Algorithm 1 is the algorithm used by historic
Algorithm 2 is the algorithm used by historic
s = sum of all bytes; r = s % 2^16 + (s % 2^32) / 2^16; cksum = (r % 2^16) + r / 2^16;
Algorithm 3 is what is commonly called the
‘ 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 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/IEC .
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 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 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.

The cksum and sum utilities exit 0 on success, and >0 if an error occurs.

md5(1)

The default calculation is identical to that given in pseudo-code
in the following
* ACM*
article.

Communications of the Tn ACM, Computation of Cyclic Redundancy Checks Via Table Lookup, August 1988.

,
The
**cksum**
utility is expected to conform to
IEEE Std 1003.2-92 ("POSIX.2").

The
**cksum**
utility appeared in
*BSD 4.4 .*

CKSUM (1) | April 28, 1995 |

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