From: Paul Brannan <pbrannan@...>
Date: 2008-03-13T00:35:36+09:00
Subject: Re: duplicating characters in a string

Some things to keep in mind:
  - captures can be slow, so if you can avoid them, you can get better
    performance
  - looping using "for" is usually faster than using "each { ... }",
    because it doesn't have to create a new scope every time the block
    is called

Three alternative solutions added given the above (my computer is slower
than yours, so I reduced the number of iterations too).  Interesting
that I was able to write an enumerator class in ruby that was faster
than the builtin enumerator class (which is written in C).  Also
interesting is how much slower the enumerator solution is on YARV:

require 'benchmark'
require 'enumerator'

class EachByteEnumerator
  def initialize(obj)
    @obj = obj
  end

  def each(&block)
    @obj.each_byte(&block)
  end
end


Benchmark.bmbm do |b|
  s = "abc" * 100_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("s.gsub(/./, '\\0\\0')") do
    s.gsub(/./, '\0\0')
  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

  b.report("7stud_enum") do
    new_str = ""
    o = s.to_enum(:each_byte)
    for byte in o do
      new_str << byte << byte
    end
  end

  b.report("7stud_enum2") do
    new_str = ""
    o = EachByteEnumerator.new(s)
    for byte in o do
      new_str << byte << byte
    end
  end
end

[pbrannan@zaphod tmp]$ ruby test.rb
Rehearsal --------------------------------------------------------
s.gsub(re) {|x| x*2}   2.410000   0.010000   2.420000 (  2.431675)
s.gsub(re, '\1\1')     0.900000   0.140000   1.040000 (  1.035942)
s.gsub(/./, '\0\0')    0.840000   0.070000   0.910000 (  0.919175)
7stud1                 1.430000   0.000000   1.430000 (  1.430979)
7stud2                 0.580000   0.010000   0.590000 (  0.585925)
7stud_enum             0.820000   0.010000   0.830000 (  0.837720)
7stud_enum2            0.510000   0.000000   0.510000 (  0.511776)
----------------------------------------------- total: 7.730000sec

                           user     system      total        real
s.gsub(re) {|x| x*2}   2.450000   0.000000   2.450000 (  2.455824)
s.gsub(re, '\1\1')     0.860000   0.010000   0.870000 (  0.861705)
s.gsub(/./, '\0\0')    0.820000   0.000000   0.820000 (  0.818279)
7stud1                 1.460000   0.010000   1.470000 (  1.483312)
7stud2                 0.590000   0.000000   0.590000 (  0.589141)
7stud_enum             0.820000   0.000000   0.820000 (  0.817231)
7stud_enum2            0.520000   0.000000   0.520000 (  0.514009)

[pbrannan@zaphod tmp]$ ruby1.9 test.rb
Rehearsal --------------------------------------------------------
s.gsub(re) {|x| x*2}   2.880000   0.030000   2.910000 (  2.961747)
s.gsub(re, '\1\1')     1.850000   0.120000   1.970000 (  1.972712)
s.gsub(/./, '\0\0')    1.770000   0.040000   1.810000 (  1.815295)
7stud1                 1.040000   0.000000   1.040000 (  1.056692)
7stud2                 0.640000   0.000000   0.640000 (  0.660844)
7stud_enum             1.710000   0.080000   1.790000 (  1.786316)
7stud_enum2            1.640000   0.120000   1.760000 (  1.770983)
---------------------------------------------- total: 11.920000sec

                           user     system      total        real
s.gsub(re) {|x| x*2}   2.950000   0.030000   2.980000 (  2.999795)
s.gsub(re, '\1\1')     1.910000   0.030000   1.940000 (  1.938242)
s.gsub(/./, '\0\0')    1.760000   0.030000   1.790000 (  1.811339)
7stud1                 1.040000   0.000000   1.040000 (  1.055916)
7stud2                 0.650000   0.030000   0.680000 (  0.685329)
7stud_enum             1.520000   0.120000   1.640000 (  1.661215)
7stud_enum2            1.450000   0.120000   1.570000 (  1.590461)

[pbrannan@zaphod tmp]$ ruby1.9 -v
ruby 1.9.0 (2008-01-24 revision 0) [i686-linux]