DATA PROCESSING USING MULTIPLY-ACCUMULATE INSTRUCTIONS

A data processing system is described utilizes a multiplier-accumulator 108 that performs both a first class of multiply-accumulate instructions and a second class of multiply-accumulate instructions. The first class of multiply-accumulate instructions are of the form N*N+N.fwdarw.N and the second class of multiply-accumulate instructions are of the form N*N+2N.fwdarw.2N. The second class of multiply-accumulate instructions provide a greater precision of arithmetic in a single instruction and avoid the use of excessive instruction set space by being constrained that the result is written back into the two registers from which the 2N-bit accumulate value was taken. The multiplier-accumulator also provides N*N.fwdarw.N and N*N.fwdarw.2N multiplication operations.