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Re: Another RFC: regex in libiberty
- To: zackw at stanford dot edu
- Subject: Re: Another RFC: regex in libiberty
- From: "Eli Zaretskii" <eliz at is dot elta dot co dot il>
- Date: Fri, 08 Jun 2001 20:32:52 +0300
- CC: dj at redhat dot com, gcc at gcc dot gnu dot org, gdb at sources dot redhat dot com, binutils at sources dot redhat dot com, cygwin at sources dot redhat dot com
- References: <20010608095932.S979@stanford.edu>
- Reply-to: Eli Zaretskii <eliz at is dot elta dot co dot il>
> From: "Zack Weinberg" <zackw@stanford.edu>
> Date: Fri, 8 Jun 2001 09:59:32 -0700
>
> On Fri, Jun 08, 2001 at 10:06:51AM +0300, Eli Zaretskii wrote:
> >
> > One notorious problem with GNU regex is that it is quite slow for many
> > simple jobs, such as matching a simple regular expression with no
> > backtracking. It seems that the main reason for this slowness is the
> > fact that GNU regex supports null characters in strings. For
> > examnple, Sed 3.02 compiled with GNU regex is about 2-4 times slower
> > on simple jobs than the same Sed compiled with Spencer's regex
> > library.
>
> I think the null characters are a red herring.
It's possible; I never had time to look into it far enough to be
sure. All I know is that the slow-down happened between two specific
versions of GNU regex, and the support for null characters was
introduced between those two versions.
> The regex.c that came with GDB 4.18, which I think is the one that got
> spread around widely, had a bug in its implementation of the POSIX
> regcomp/regexec interface, which caused a major performance hit. That
> bug has been fixed in GNU libc for a long time. When I replaced
> fixincludes' copy of regex.c with a more recent version from glibc,
> fixincludes was sped up by a factor of nine. That same bug affects
> Sed 3.02 - replace the regex.c it ships with with the one from glibc
> 2.2.x and I bet you'll see better performance.
>
> There's some discussion in these messages:
>
> http://gcc.gnu.org/ml/gcc-patches/2000-01/msg00764.html
> http://gcc.gnu.org/ml/gcc-patches/2000-01/msg00765.html
Thanks for the pointers.
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