Hi Norihiro.
sed and gawk use fastmap in regex, but grep does not. By using fastmap,
I expect that grep speeds up for patterns as regex is used.
before:
$ time -p env LC_ALL=ja_JP.eucjp src/grep '\([a-b]\)\1' k
real 7.83
user 7.62
sys 0.07
after:
$ time -p env LC_ALL=ja_JP.eucjp src/grep '\([a-b]\)\1' k
real 0.46
user 0.38
sys 0.07
However, if grep uses fastmap, fails in case-fold-titlecase test. It
means that grep's behavior differ from sed and gawk, as they use fastmap,
although it seems to be a bug in regex.
Wow, that is a spectacular speed improvement. Since I use grep with regex
patterns heavily in some of my scripts I could not resist to make some
first simple tests (including your example pattern with a back reference).
The non-representative results using grep 2.25 shows a gain of a factor
5-10 (while the unpatched self-compiled grep 2.25 itself was already a
factor 1.4-2.8 faster than the grep 2.16 offered by the OS (OpenSUSE Leap
42.1). At least in my tests all the grep outputs were identical.
By the way I had to remove one of the two "=" in your patch otherwise gcc
issued an error (but caution, I am a C-layman).
Regards
Jens
