A processor for calculating a convolution of a first input sequence of numbers with a second input sequence of numbers to generate an output sequence is provided. The processor includes multipliers, each multiplying two real numbers to generate an output; multiplexers to direct the numbers in the first and second input sequences or parts of the numbers to the multipliers; and control circuitry to control the multiplexers to direct the first and second input sequences of numbers to the multipliers dependent on whether the numbers are complex or real. An accumulator adds partial products from multiplications performed by the multipliers to calculate the convolution.