math/big: faster string conversion routines
Eliminated unnecessary string conversions throughout and removed
(internal) capability for arbitrary character sets in conversion
routines (functionality was not exported and not used internally).
benchmark old ns/op new ns/op delta
BenchmarkDecimalConversion-8 198283 187085 -5.65%
BenchmarkStringPiParallel-8 46116 47822 +3.70%
BenchmarkString10Base2-8 216 166 -23.15%
BenchmarkString100Base2-8 886 762 -14.00%
BenchmarkString1000Base2-8 7296 6625 -9.20%
BenchmarkString10000Base2-8 72371 65563 -9.41%
BenchmarkString100000Base2-8 725849 672766 -7.31%
BenchmarkString10Base8-8 160 114 -28.75%
BenchmarkString100Base8-8 398 309 -22.36%
BenchmarkString1000Base8-8 2650 2244 -15.32%
BenchmarkString10000Base8-8 24974 21745 -12.93%
BenchmarkString100000Base8-8 245457 217489 -11.39%
BenchmarkString10Base10-8 337 288 -14.54%
BenchmarkString100Base10-8 1298 1046 -19.41%
BenchmarkString1000Base10-8 6200 5752 -7.23%
BenchmarkString10000Base10-8 24942 22589 -9.43%
BenchmarkString100000Base10-8
8012921 7947152 -0.82%
BenchmarkString10Base16-8 156 107 -31.41%
BenchmarkString100Base16-8 344 255 -25.87%
BenchmarkString1000Base16-8 2067 1705 -17.51%
BenchmarkString10000Base16-8 19026 16112 -15.32%
BenchmarkString100000Base16-8 184038 163457 -11.18%
Change-Id: I68bd807529bd9b985f4b6ac2a87764bcc1a7d2f7
Reviewed-on: https://go-review.googlesource.com/14926
Reviewed-by: Alan Donovan <adonovan@google.com>