[jruby-dev] [jira] Created: (JRUBY-5619) String#to_f slower than Rubinius impl

[Charles Oliver Nutter (JIRA)]

String#to_f slower than Rubinius impl
-------------------------------------

                 Key: JRUBY-5619
                 URL: http://jira.codehaus.org/browse/JRUBY-5619
             Project: JRuby
          Issue Type: Improvement
          Components: Performance
    Affects Versions: JRuby 1.6
            Reporter: Charles Oliver Nutter


Rubinius's implementation of String#to_f (which is entirely native) appears to 
be faster than our implementation. There's room for improvement, then.

Here's the benchmark, from Rubinius's suite:

{noformat}

require 'benchmark'
require 'benchmark/ips'

Benchmark.ips do |x|
  int = "5"
  float = "5.0"
  empty = ""
  with_extra_text = "5.0 and some extra characters"

  x.report "#to_f with an integer in a string" do |times|
    i = 0
    while i < times
      int.to_f
      i += 1
    end
  end

  x.report "#to_f with a float in a string" do |times|
    i = 0
    while i < times
      float.to_f
      i += 1
    end
  end

  x.report "#to_f with an empty string" do |times|
    i = 0
    while i < times
      empty.to_f
      i += 1
    end
  end

  x.report "#to_f with a float and trailing text" do |times|
    i = 0
    while i < times
      with_extra_text.to_f
      i += 1
    end
  end
end
{noformat}

And the results. We are faster than 1.9 on every one, but slower than Rubinius 
on all but the empty string case:

{noformat}

~/projects/rubinius &#10132; jruby --server -I benchmark/lib/ 
benchmark/core/string/bench_to_f.rb 
#to_f with an integer in a string
                      4492873.5 (±10.5%) i/s -   21610008 in   4.926805s 
(cycle=19416)
#to_f with a float in a string
                      4090389.9 (±7.3%) i/s -   20168125 in   4.972809s 
(cycle=38125)
#to_f with an empty string
                      8870004.5 (±4.9%) i/s -   43788240 in   4.949856s 
(cycle=47856)
#to_f with a float and trailing text
                      3242020.7 (±2.9%) i/s -   16122936 in   4.977419s 
(cycle=39517)

~/projects/rubinius &#10132; ruby1.9 -I benchmark/lib/ 
benchmark/core/string/bench_to_f.rb 
#to_f with an integer in a string
                      3297930.1 (±11.4%) i/s -   16248152 in   5.002084s 
(cycle=51256)
#to_f with a float in a string
                      3249934.5 (±9.6%) i/s -   16120108 in   5.010589s 
(cycle=51013)
#to_f with an empty string
                      3436553.5 (±9.8%) i/s -   16996986 in   4.997253s 
(cycle=51042)
#to_f with a float and trailing text
                      2663843.9 (±7.0%) i/s -   13292916 in   5.017321s 
(cycle=48692)

~/projects/rubinius &#10132; bin/rbx -I benchmark/lib/ 
benchmark/core/string/bench_to_f.rb 
#to_f with an integer in a string
                      5279759.2 (±1.9%) i/s -   26302185 in   4.983932s 
(cycle=44961)
#to_f with a float in a string
                      5025081.5 (±1.2%) i/s -   25065360 in   4.988854s 
(cycle=40428)
#to_f with an empty string
                      5868962.7 (±2.8%) i/s -   29244904 in   4.987846s 
(cycle=47864)
#to_f with a float and trailing text
                      4398309.3 (±19.2%) i/s -   19126856 in   4.984183s 
(cycle=46312)
{noformat}

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