encoding: add fast path of from/tolocal() for ASCII strings This is micro optimization, but seems not bad since to/fromlocal() is called lots of times and isasciistr() is cheap and simple. We boldly assume that any non-ASCII characters have at least one 8-bit byte. This isn't true for some email character sets (e.g. ISO-2022-JP and UTF-7), but I believe no such encodings are used as a platform default. Shift_JIS, a major crap, is okay as it should have a leading byte in 0x80-0xff range. (with mercurial repo) $ export HGRCPATH=/dev/null HGPLAIN= $ hg log --time --config experimental.stabilization=all > /dev/null (original) time: real 7.460 secs (user 7.420+0.000 sys 0.030+0.000) time: real 7.670 secs (user 7.590+0.000 sys 0.080+0.000) time: real 7.560 secs (user 7.510+0.000 sys 0.040+0.000) (this patch) time: real 7.340 secs (user 7.260+0.000 sys 0.060+0.000) time: real 7.260 secs (user 7.210+0.000 sys 0.030+0.000) time: real 7.310 secs (user 7.260+0.000 sys 0.060+0.000)