From: Joel VanderWerf <vjoel@...>
Date: 2008-03-08T13:45:24+09:00
Subject: Re: duplicating characters in a string

7stud -- wrote:
> And taking your non-perl champion:
> 
> s.gsub(/(.)/, '\1\1')
> 
> (I refuse to consider any code that uses perl syntax), and pitting it 
> against:
> 
> s = 'abc'
> new_str = ""
> s.each_byte do |byte|
>   2.times do
>     new_str << byte
>   end
> end
> 
> 
> I get:
> 
> gsub:
> t1 exec time(1,000,000 loops): 5.625847 total
> 
> each_byte:
> t2 exec time(1,000,000 loops): 5.325978 total

Hm, I don't see an improvement, unless I replace 2.times... with an 
explicit unrolling of that inner loop (which is heading downhill in the 
elegance department):

require 'benchmark'

Benchmark.bmbm do |b|
   s = "abc" * 1_000_000
   re = /(.)/

   b.report("s.gsub(re) {|x| x*2}") do
     s.gsub(re) {|x| x*2}
   end

   b.report("s.gsub(re, '\1\1')") do
     s.gsub(re, '\1\1')
   end

   b.report("7stud1") do
     new_str = ""
     s.each_byte do |byte|
       2.times do
         new_str << byte
       end
     end
   end

   b.report("7stud2") do
     new_str = ""
     s.each_byte do |byte|
       new_str << byte << byte
     end
   end
end

__END__

Rehearsal ---------------------------------------------------
s.gsub(re){...}   6.220000   0.010000   6.230000 (  6.325230)
s.gsub(re,...)    3.020000   0.060000   3.080000 (  3.115286)
7stud             4.110000   0.000000   4.110000 (  4.142912)
7stud             2.050000   0.000000   2.050000 (  2.072398)
----------------------------------------- total: 15.470000sec

                       user     system      total        real
s.gsub(re){...}   5.910000   0.020000   5.930000 (  5.993456)
s.gsub(re,...)    3.000000   0.000000   3.000000 (  3.017119)
7stud             4.100000   0.020000   4.120000 (  4.300772)
7stud             2.030000   0.010000   2.040000 (  2.068190)

-- 
       vjoel : Joel VanderWerf : path berkeley edu : 510 665 3407