Going way back into history, the Alesis MIDIVerb reverb unit had a really simple DSP core made out of discrete logic chips. It could add a memory location to an accumulator and divide it by two, invert it, add it and divide it by two, or store it in ram either inverted or not and divide the accumulator by two.

Four instructions, in about eight chips.

By combining shifts and adds Keith Barr was able to devise all the different filter and delay coefficients for 63 different reverb programs (the 64th one was just dead passthrough).