bug#24071: [PATCH] Refactor regex character class parsing in [:name:]

[Eli Zaretskii <eliz@gnu.org>]

> From: Michal Nazarewicz <mina86@mina86.com>
> Date: Tue, 26 Jul 2016 00:54:05 +0200
> 
> re_wctype function is used in three separate places and in all of
> those places almost exact code extracting the name from [:name:]
> surrounds it.  Furthermore, re_wctype requires a NUL-terminated
> string, so the name of the character class is copied to a temporary
> buffer.
> 
> The code duplication and unnecessary memory copying can be avoided by
> pushing the responsibility of parsing the whole [:name:] sequence to
> the function.
> 
> Furthermore, since now the function has access to the length of the
> character class name (since it’s doing the parsing), it can take
> advantage of that information in skipping some string comparisons and
> using a constant-length memcmp instead of strcmp which needs to take
> care of NUL bytes.

Thanks.

If we are going to make some serious refactoring in regex.c, I think
we should start with having a test suite for it.  The
dima_regex_embedded_modifiers branch, created by Dima Kogan (CC'ed) in
the Emacs repository includes a suite taken from glibc.  Dima, could
you perhaps merge the parts of the test suite that can already be used
to the master branch, so that we could use them to verify changes in
regex.c?