From: Jason Roelofs <jameskilton@...>
Date: 2007-03-20T23:30:05+09:00
Subject: Re: Regexp and Prime numbers

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On 3/20/07, Tim Pease <tim.pease@gmail.com> wrote:
>
> On 3/20/07, gga <GGarramuno@aol.com> wrote:
> > On Mar 19, 4:07 pm, "Tim Pease" <tim.pe...@gmail.com> wrote:
> > >
> > > ruby -wle 'puts "Prime" unless ("1" * ARGV[0].to_i) =~
> /^1$|^(11+?)\1+$/' 42
> > >
> >
> > This is pretty cool.  Particularly as a simple benchmark for regex
> > backtracking.
> > It highlites some of the performance issues of backtracking in ruby1.8
> > and 1.9.
> > And it also highlites issues with Perl's backtracking.
> >
> > Speed issues:
> > > time ruby1.9 -wle 'puts "Prime" unless ("1" * ARGV[0].to_i) =~
> /^1$|^(11+?)\1+$/' 22441
> > Prime
> >
> > real    0m2.111s
> > user    0m2.084s
> > sys     0m0.024s
> >
> > > time perl -wle 'print "Prime" if (1 x shift) !~ /^1$|^(11+?)\1+$/'
> 22441
> > Prime
> >
> > real    0m0.230s
> > user    0m0.208s
> > sys     0m0.020s
> >
> >
> > But... on larger numbers...
> >
> > > ruby1.9 -wle 'puts "Prime" unless ("1" * ARGV[0].to_i) =~
> /^1$|^(11+?)\1+$/' 104729
> > Prime
> >
> > > perl -wle 'print "Prime" if (1 x shift) !~ /^1$|^(11+?)\1+$/' 104729
> > Segmentation fault
> >
> > > perl -v
> > This is perl, v5.8.8 built for x86_64-linux-gnu-thread-multi
> >
>
> Now that is very interesting.  Do you know if Ruby 1.9 is running
> Onigurma <sp?>, the new regexp handler?
>
>
For those of us on Windows command line:

ruby -wle "puts 'Prime' unless ('1' * ARGV[0].to_i) =~ /^1$|^(11+?)\1+$/"

That's cool.

Jason

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