internal/chacha20: cache first round across XORKeyStream invocations
name old speed new speed delta
ChaCha20/64-4 428MB/s ± 1% 432MB/s ± 1% ~ (p=0.089 n=10+10)
ChaCha20/256-4 497MB/s ± 1% 507MB/s ± 2% +1.94% (p=0.000 n=9+10)
ChaCha20/10x25-4 273MB/s ± 1% 285MB/s ± 3% +4.37% (p=0.000 n=10+10)
ChaCha20/4096-4 495MB/s ± 1% 508MB/s ± 1% +2.51% (p=0.000 n=8+10)
ChaCha20/100x40-4 407MB/s ± 1% 439MB/s ± 1% +7.92% (p=0.000 n=9+9)
ChaCha20/65536-4 521MB/s ± 2% 537MB/s ± 1% +3.00% (p=0.000 n=10+10)
ChaCha20/1000x65-4 498MB/s ± 2% 521MB/s ± 2% +4.70% (p=0.000 n=10+10)
Curiously, even if we omit the critical s.precompDone = true step, we
see a significant performance improvement across the board, maybe due to
reduced register pressure. (See below. Actually using the precomputed
values only impacts the 10x25, 100x40 and 1000x65 benchmarks, as
expected.)
name old speed new speed delta
ChaCha20/64-4 428MB/s ± 1% 428MB/s ± 1% ~ (p=0.912 n=10+10)
ChaCha20/256-4 497MB/s ± 1% 510MB/s ± 1% +2.64% (p=0.000 n=9+10)
ChaCha20/10x25-4 273MB/s ± 1% 277MB/s ± 2% +1.36% (p=0.003 n=10+10)
ChaCha20/4096-4 495MB/s ± 1% 507MB/s ± 2% +2.28% (p=0.000 n=8+10)
ChaCha20/100x40-4 407MB/s ± 1% 418MB/s ± 1% +2.69% (p=0.000 n=9+10)
ChaCha20/65536-4 521MB/s ± 2% 536MB/s ± 1% +2.76% (p=0.000 n=10+8)
ChaCha20/1000x65-4 498MB/s ± 2% 519MB/s ± 1% +4.15% (p=0.000 n=10+9)
Updates golang/go#24485
Change-Id: I117fab938787819aae1cc4371354888701e4e54b
Reviewed-on: https://go-review.googlesource.com/c/crypto/+/185440
Reviewed-by: Michael Munday <mike.munday@ibm.com>
Filippo Valsorda
9b708ad8e1