original_query: What is the purpose of the table computed by the YM3812?
query: What is the purpose of the lookup tables computed by the YM3812?
answer: The YM3812 uses two 256-word lookup tables: one for calculating exponents (to convert logarithmic scale signals back to linear scale) and one for a quarter of a log-transformed sine wave (the rest is extrapolated).  This avoids computationally expensive multiplications, using additions instead.