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Jeffrey Walton 2018-10-26 03:12:46 -04:00
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chacha-simd.cpp
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@ -9,6 +9,19 @@
// SSE2 implementation based on Botan's chacha_sse2.cpp. Many thanks
// to Jack Lloyd and the Botan team for allowing us to use it.
//
// The SSE2 implementation is kind of unusual among Crypto++ implementations.
// We guard on SSE2 and use HasSSE2(). However, if a target machine has
// SSSE3 or XOP available (say, by -march=native), then we can pull another
// 200 to 500 MB/s out of ChaCha. To capture SSSE3 and XOP we use the compiler
// defines __SSSE3__ and __XOP__ and forgo runtime tests.
//
// Runtime tests for HasSSSE3() and HasXop() are too expensive. The rotates
// are on a critical path and the runtime tests crush performance.
//
// Here are some relative numbers for ChaCha8:
// * Intel Skylake, 3.0 GHz: SSE2 at 2000 MB/s; SSSE3 at 2350 MB/s.
// * AMD Bulldozer, 3.3 GHz: SSE2 at 2140 MB/s; XOP at 2550 MB/s.
//
// Power8 is upcoming.
#include "pch.h"