Optimization to regexp _CharClass: keep track of overall range of
charclass to avoid unnecessarily iterating over ranges.
Also, use the fact that IntVector is an []int to avoid method calls.
On my machine, this brings us from ~27500 ns/op to ~17500 ns/op in the benchmark I've added (it is also faster in the case where a range check
doesn't help, added a benchmark for this too.)
I'd also like to propose that "[]", and "[^]" be disallowed. They aren't useful as far as I can tell, they aren't widely supported, and they make reasoning about character classes a bit more complicated.
R=r
CC=golang-dev
https://golang.org/cl/
1495041