math/big: save some copies in binaryGCD.
This patch resulted from a bit of quick optimisation in response to a
golang-nuts post. It looks like one could save a couple other copies in
this function, but this addresses the inner loop and is fairly simple.
benchmark old ns/op new ns/op delta
BenchmarkGCD10x10 1964 1711 -12.88%
BenchmarkGCD10x100 2019 1736 -14.02%
BenchmarkGCD10x1000 2471 2171 -12.14%
BenchmarkGCD10x10000 6040 5778 -4.34%
BenchmarkGCD10x100000 43204 43025 -0.41%
BenchmarkGCD100x100 11004 8520 -22.57%
BenchmarkGCD100x1000 11820 9446 -20.08%
BenchmarkGCD100x10000 23846 21382 -10.33%
BenchmarkGCD100x100000 133691 131505 -1.64%
BenchmarkGCD1000x1000 120041 95591 -20.37%
BenchmarkGCD1000x10000 136887 113600 -17.01%
BenchmarkGCD1000x100000 295370 273912 -7.26%
BenchmarkGCD10000x10000
2556126 2205198 -13.73%
BenchmarkGCD10000x100000
3159512 2808038 -11.12%
BenchmarkGCD100000x100000
150543094 139986045 -7.01%
R=gri, remyoudompheng
CC=bradfitz, gobot, golang-dev, gri
https://golang.org/cl/
9424043