On Fri, Jul 30, 1999 at 03:27:20PM +0200, Dag-Erling Smorgrav wrote:
>
> Funnily, I experience a near-doubling of running time with similar
> patches.
Incidentally, it seems that it's not possible to assume that our
regex library is even anywhere in the same league as the GNU regex
library.
b$ time ./grep -E '(vt100)|(printer)' longfile > /dev/null
real 0m21.284s
user 0m22.034s
sys 0m0.083s
Now, with a profiled executable with optimization turned off it
takes about 25 seconds. Regardless, it appears to spend 98% of
its time in regexec(), which is good, since that's where it should
be spending time.
[I had been intending to combine multiple patterns, ultimately
combining in a '\n' to avoid the memchr() in mmopen].
b$ time grep '(vt100)|(printer)' longfile > /dev/null
real 0m0.267s
user 0m0.109s
sys 0m0.157s
98% * 20 = ~19... Without an improved regex library, any mildly
complicated pattern will bring the new grep to its knees.
This could be the dfa helping GNU grep more than having a better
regexp library... Probably both.
I wonder how well the devel/pcre port would do POSIX regular expressions.
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