crypto/hmac: simplify implementation
Store already padded keys instead of storing key and padding it during
Reset and Sum. This simplifies code and makes Reset-Write-Sum sequences
faster, which helps /x/crypto/pbkdf2.
HMAC benchmark:
benchmark old ns/op new ns/op delta
BenchmarkHMACSHA256_1K-4 7669 7613 -0.73%
BenchmarkHMACSHA256_32-4 1880 1737 -7.61%
benchmark old MB/s new MB/s speedup
BenchmarkHMACSHA256_1K-4 133.52 134.50 1.01x
BenchmarkHMACSHA256_32-4 17.02 18.41 1.08x
PBKDF2 benchmark:
benchmark old ns/op new ns/op delta
BenchmarkPBKDF2HMACSHA256-4
1943196 1807699 -6.97%
Change-Id: I6697028370c226715ab477b0844951a83eb3488c
Reviewed-on: https://go-review.googlesource.com/21024
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Adam Langley <agl@golang.org>