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- 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.
Simple DirectMedia Layer (SDL) Version 2.0
Simple DirectMedia Layer is a cross-platform development library designed to provide low level access to audio, keyboard, mouse, joystick, and graphics hardware via OpenGL and Direct3D. It is used by video playback software, emulators, and popular games including Valve's award winning catalog and many Humble Bundle games.
More extensive documentation is available in the docs directory, starting with README.md
Enjoy!
Sam Lantinga (slouken@libsdl.org)