DIGITAL SIGNAL PROCESSING

For more convenient mechanisation, the modulo m reduction of a binary number P can be carried out by conditionally summing the modulo m reductions of a power series of two and then modulo m reducing the sum. The modulo m reductions of the series, called the 'residues' of the series, can be pre-calculated and stored but this may be inconvenient if they are long in terms of numbers of bits. Herein, the residues are calculated in sequence by a recursive process, each residue being calculated from the next preceeding one, this leading to a 'serial' arrangement for generating the residues which can be incorporated into a serial modulo m reduction unit. Such a serial modulo m reduction unit is convenient for implementation as an integrated circuit especially as part of an overall circuit for encryption and decryption of digital signals.