bug#16544: Optimazation for is_mb_middle

[Norihiro Tanaka]

Package: grep
Tags: patch

When matched characters to a regular expression is found by kwsexec or
dfaexec, we need check whether it is in the middle of a multi-byte character.

`is_mb_middle' of searchutils.c is used for it. However, it's expensive,
even if most of them contain constitute with single-byte characters.
For example, a source code written in a language with multibyte characters,
has a lot of single-byte characters.

Now, I post the patch which optimizes `is_mb_middle'. It checks whether
each single-byte is completion as an character before execution, and
caches them. In addition, for UTF-8 further optimization is performed.

Only when it's impossible to determine the length of a multibyte character
with caches, the length is determined with `mbrlen' in execution.

is_mb_middle.txt
Description: Binary data