curve25519: improve cswap
Simplify the constant swap function.
On amd64: Replace the CMOVQEQ scheme with SSE2 code similar to the non-amd64 code.
On non-amd64: Avoid unnecessary loop iterations.
The result is less and slightly faster code.
name old time/op new time/op delta
ScalarBaseMult-4 653µs ± 0% 636µs ± 0% ~ (p=0.100 n=3+3)
name old time/op new time/op delta
ConstantSwap-4 10.4ns ± 1% 6.2ns ± 0% -39.86% (p=0.029 n=4+4)
On an i7-65000U
Change-Id: Ia5eea92e0b3eabb6c291d25229aa582b51278552
Reviewed-on: https://go-review.googlesource.com/39693
Reviewed-by: Adam Langley <agl@golang.org>
Run-TryBot: Adam Langley <agl@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
3 files changed
