benchmark                old ns/op    new ns/op    delta
BenchmarkDecodeDigits     19451173     14347829  -26.24%
BenchmarkDecodeTwain      57516800     42619978  -25.90%

benchmark                 old MB/s     new MB/s  speedup
BenchmarkDecodeDigits         2.22         3.01    1.36x
BenchmarkDecodeTwain          2.17         2.93    1.35x

R=golang-dev, dave, bradfitz, agl
CC=golang-dev
https://golang.org/cl/9915043