(recode.info)Permutations

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Permuting groups of bytes
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   A permutation is a surface transformation which reorders groups of
eight-bit bytes.  A _21_ permutation exchanges pairs of successive
bytes.  If the text contains an odd number of bytes, the last byte is
merely copied.  An _4321_ permutation inverts the order of quadruples
of bytes.  If the text does not contains a multiple of four bytes, the
remaining bytes are nevertheless permuted as _321_ if there are three
bytes, _21_ if there are two bytes, or merely copied otherwise.

`21'
     This surface is available in `recode' under the name
     `21-Permutation' and has `swabytes' for an alias.

`4321'
     This surface is available in `recode' under the name
     `4321-Permutation'.