Re: Regular expression libraries

[Clément Pit--Claudel]

On 2016-12-16 02:20, Paul Eggert wrote:
> Andreas Schwab wrote:
>>> Another library is in that list:
>>> 
>>> - The GNU C library, which ordinarily uses a DFA but which uses 
>>> backtracking if needed.
>> But it doesn't support a gap.
> 
> True, but none of the others do either. Only the old glibc code
> (which survives only in Emacs now) does that, as far as I know.

TRE does.

> I doubt whether it'd be that hard to add gap support to any regexp
> matcher, as it's simply interposing an address calculation.

I did ask both the Oniguruma and the RE2 people; neither were optimistic 
(admittedly, my question was about supporting a slightly more general form than 
2 chunks).  In RE2, there are optimizations like using memchr to find the next 
character within a memory region, which are tricky to use if address 
calculations are added into the mix.

Clément.

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