Optimize me! (C, performance) — followup to bit-twiddling question?

You seem to be wasting much time doing divisions by the factors. It is much faster to replace a division with a multiplication by the reciprocal of divisor (division: ~15-80(! ) cycles, depending on the divisor, multiplication: ~4 cycles) IF of course you can precompute the reciprocals.

If your compiler supports GCC function attributes, you can mark your pure functions with this attribute.

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