CIRCUIT ARRANGEMENT COMPRISING A PERMUTATION UNIT CIRCUIT ARRANGEMENT COMPRISING A PERMUTATION UNIT AND METHOD OF PROCESSING A BATCH OF ITEMS AND METHOD OF PROCESSING A BATCH OF ITEMS

摘要

The circuit arrangement calculates pseudo-random permutations of a set of numbers. It is required that the permutations that can be calculated by the circuit arrangement include compositions of some basic pseudo-random permutations and the inverse permutations of permutations that are calculated (a composition corresponds to cumulatively repeated reordering of the numbers, an inverse of a permutation is a permutation that undoes the permutation). 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 fi. The generator calculates the permutations σ(n) of the numbers n=O..m-1 corresponding to I, whereα 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(α) of two or higher. When the same α 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.