The OPL chips use two look-up tables, each containing 256 entries. [https://g.co/kgs/Da1vEi4 Source]
It produces They produce the sound without any multiplication or other costly arithmetic operations, using for 2-op "frequency modulated" (actually phase modulated) synthesis the formula:
out = exp(logsin(phase2 + exp(logsin(phase1) + gain1)) + gain2)