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…ground truth sin_cos occasionally
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Computes twiddles on the fly in the variable-size kernel instead of caching them.
This reduces memory usage since the twiddles no longer need to be stored. When combined with #95 we need no auxiliary memory at all for the entire FFT process, including interleaving/deinterleaving and bit reversal.
Zen4 results: on large sizes this is neutral on a single thread and a 12% improvement when multi-threaded. However, small sizes that are not memory-bound do take a large performance penalty, with up to 60% more time taken.
M4 seems to benefit from this on large sizes.
Detailed benchmarks:
Single threaded:
Zen4: https://gist.github.com/Shnatsel/55e32f567c6f1a99ee96f2713bc89b5a
M4: https://gist.github.com/Shnatsel/2695ba6fbc3263a2679f045db5546127
Multi-threaded:
Zen4: https://gist.github.com/Shnatsel/3db0fe24d59c7e4a9a923a1b47653ca0
M4: https://gist.github.com/Shnatsel/e03e1cd148e5208b15448d01223ed5a8