What do codecs have to do with grep?

grep respects LC_CTYPE, so it has to handle text encoding (or rely on something else that does, like libc or iconv).

However, by the same token, we might as well count any assembly in the kernel that gets executed due to some syscall from grep.

Those are locales. I've never heard them referred to as "codecs."

In any case, I'd still like to see a grep whose inner loop is written in Assembly. :-)

"en_US.UTF-8" is a locale. The "UTF-8" part is the encoding of that locale. Codec would be whatever piece of code parses the encoding.

>in the kernel that gets executed due to some syscall from grep

That won't be considered 'inner loop'