Galois field computer

Abstract

Errors are corrected in a cyclic encoded data stream, consisting of sequential groups of data bits and check bits, by means of a novel digital computer. The computer employs a stored program and is organized into three distinct substructures, each having an independent internal addressable memory and all capable of synchronous concurrent operation. An arithmetic unit substructure including a data memory implements finite field arithmetic operations upon received data. The arithmetic unit includes a Galois field manipulative subunit for producing finite field products and sums over the field GF(2.sup.5) from operands selected from three registers which derive data from the memory of the arithmetic unit, another register, or the result of a currently executed Galois field operation. The preferred embodiment is especially suitable for correcting data encoded in the Reed-Solomon (31,15) code. An address generator realizes address modification in the Galois field GF(2.sup.7), whereby consecutive addresses in data memory are characterized by a shift register sequence. The address generator includes a counter memory array and an equality test facility. Counter memory words of the address generator may selectably retain either the modified or non-modified address. A control unit substructure includes a control memory for storage and execution of the instruction sequence, branching logic for determining the transfer of control in response to logical functions of up to 16 logical variables, and select means and gating means for execution of instructions in all three substructures. Provision for data dependent arithmetic function selection, not employed for decoding the (31,15) Reed Solomon Code, permits the operation of the apparatus to yield solutions at high speed to simultaneous linear binary equations.