sha256: small speedup for sse4 path. #13400
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ACK, benchmarked to be around 5% faster for SSE4 (when disabling the AVX2 code on my i7-7820HQ). |
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Sadly, @laanwj saw a 25% penalty for this change on pre-avx2 AMD. Closing :( |
theuni
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The algorithm used to calculate Sigma0/Sigma1 here is the same as the one used in bitcoin#13400, which resulted in a ~5% speedup on Intel CPUs, but close to 25% penalty on AMD. So unfortunately, this should result in a ~5% slowdown on Intel. However, bitcoin#13400 was operating on 128bit registers and these are 32bit, it's possible that there's no penalty on AMD, and this change is not needed.
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This is an optimization described in the intel sha256 whitepaper (page 10). It speeds up the SHA256D64_1024 bench (sse4 path, no avx2) for me by ~6%.