kc3-lang/SDL

2022-04-10T13:23:51

audio: Resampler optimizations. - Calculate `j * RESAMPLER_SAMPLES_PER_ZERO_CROSSING` once per loop iteration since we use it multiple times. - Do the left-wing loop in two sections: while `srcframe < 0` and then the remaining calculations when `srcframe >= 0`. This bubbles a conditional out of every iteration of a tight loop, giving us a boost. We could _probably_ do this to the right-wing loop too, but it's less straightforward there. - The real win: Use floats instead of doubles. This almost doubles the speed of the entire function on Intel CPUs, and for embedded things without hardware-level support for doubles, the speedup is enormous. This in theory might reduce audio quality, though, and I had to put a check in place to avoid a division-by-zero that we avoided at higher precision, but this is likely to be worth keeping for at least the Sony PSP and other smaller platforms, if not everyone.