Circuit arrangement comprising a permutation unit and method of

Abstract

A circuit arrangement calculates pseudo-random permutations of a set of numbers. Including compositions of some basic pseudo-random permutations and the inverse permutations of permutations that are calculated. The basic pseudo-random permutations, their compositions and inverses are all calculated by the same generator whose operation is commanded to calculate the appropriate permutation by specifying a set of integer coefficients f.sub.i. The generator calculates the permutations .sigma.(n) of the numbers n=0 . . . m-1 corresponding to ##EQU1## where .alpha. is an integer number which is divisible by all prime factors of m and by four if m is divisible by four, with a potency s(.alpha.) of two or higher. When the same a is used for all permutations it is assured that all compositions and inverses of the generated permutations can be calculated in the same way, by the same generator. By storing a batch of items in a storage medium in a first order and retrieving the items from the storage medium in a second order, the first and second order corresponding to different permutations which are both of this type, it is made possible to permute the batch pseudo randomly and start storing the batch of items in the storage medium before a previous batch has been fully retrieved from it.