That would be quite a big lookup table... Half of float numbers are in -1…+1 range. You don't need the negative part, so that's a quarter of float numbers, over

That would be quite a big lookup table... Half of float numbers are in -1…+1 range. You don't need the negative part, so that's a quarter of float numbers, over one billion numbers. And then some to get from 1 to π/2. And that's only float32!