From: Devin Mullins <twifkak@...>
Date: 2006-09-05T23:10:11+09:00
Subject: Re: Benchmarking (Was: Re: Compiling Regexp only once)

Eric Hodel wrote:
> So literal regular expressions are "faster" by about 56% (after  
> discounting loop overhead) (when you're performing 100 million  
> retrievals only) (actual speedup in real code will probably be  
> swallowed elsewhere or completely irrelevant).
> 
> This follows from reading eval.c.  Constant lookup involves a bunch  of 
> C function calls, but literal lookup just returns an Object stored  in 
> the parse tree.
Interesting. Note that this is different from your benchmark in 
ruby-talk:204747, wherein much of the savings seems to come from not 
having to instantiate & populate a MatchData. Compare:

require 'benchmark'

N = 1_000_000

string = 'a b c d e'

Benchmark.bmbm do |bm|

    bm.report 'empty' do
      N.times do end
    end

    bm.report 'none' do
      N.times do string =~ /a (.) c\s. e/ end
    end

    bm.report '5' do
      N.times do string =~ /a (.) c\s. e/;5 end
    end

    bm.report '$1' do
      N.times do string =~ /a (.) c\s. e/;$1 end
    end

    bm.report '$&' do
      N.times do string =~ /a (.) c\s. e/;$& end
    end

    bm.report '$~' do
      N.times do string =~ /a (.) c\s. e/;$~ end
    end

    bm.report 'match' do
      N.times do string.match /a (.) c\s. e/ end
    end
end
__END__

Rehearsal -----------------------------------------
empty   0.141000   0.000000   0.141000 (  0.204000)
none    1.453000   0.000000   1.453000 (  1.500000)
5       1.578000   0.000000   1.578000 (  1.625000)
$1      3.500000   0.015000   3.515000 (  3.546000)
$&      3.640000   0.000000   3.640000 (  3.875000)
$~      4.641000   0.016000   4.657000 (  4.922000)
match   5.313000   0.015000   5.328000 (  5.422000)
------------------------------- total: 20.312000sec

             user     system      total        real
empty   0.156000   0.000000   0.156000 (  0.156000)
none    1.484000   0.000000   1.484000 (  1.531000)
5       1.563000   0.000000   1.563000 (  1.610000)
$1      3.468000   0.000000   3.468000 (  3.937000)
$&      3.484000   0.000000   3.484000 (  3.875000)
$~      4.609000   0.016000   4.625000 (  4.641000)
match   5.219000   0.016000   5.235000 (  5.313000)

Devin