I am currently doing an optimised sin using a lookup table and given I have seen some bitwise magic posted before I was wondering what people could come up with for this problem:

Given power of 2 sized table containing a quarter sine wave what is the best way to get the table index/sign for the output.



Now you can just use conditionals to calculate each of the quadrants but if you convert phase to an integer using TABLE.length*4 the top two bits give you the sign and flip for the quarter wave. I have come up with some mashing that gives you the index and sign but I'm sure there is an easier way two exploit 2's compliment and modular to get the answer.  Bonus points for efficient linear interpolation.

If you want bit magic for the fun of it...



I think...

Do you know if a floatToRawIntBits can be performed faster than a float->int cast? I might try comparing them at some point, but if it can be then:



for a 256 length table. For 512 then shift by 14, and mask with 0x1FF, etc. The idea being to keep the float within one power-of-two fraction, and just use the most significant mantissa bits.

This assumes that the range is from 0-1.0f, excluding 1.0f.

Edit: This isn't actually answering the original question, sorry. Just a thought of an alternative to the float cast.