math/rand: minor optimization to Perm
Instead of writing out 0..n and then reading it
back, just use i when it is needed.
Wikipedia calls this the "inside-out" implementation:
http://en.wikipedia.org/wiki/Fisher%E2%80%93Yates_shuffle
This yields identical values to the previous
implementation, given the same seed. (Note that the
output from Example_rand is unchanged.)
2.8 GHz Intel Core i7, results very stable:
benchmark old ns/op new ns/op delta
BenchmarkPerm3 138 136 -1.45%
BenchmarkPerm30 825 803 -2.67%
Stock Raspberry Pi, minimum improvement out of three runs:
benchmark old ns/op new ns/op delta
BenchmarkPerm3 5774 5664 -1.91%
BenchmarkPerm30 32582 29381 -9.82%
R=golang-dev, dave, mtj, adg
CC=golang-dev
https://golang.org/cl/
21030043