Hitokage - Faster Float#to_s

The ruby's Float#to_s uses David M. Gay's library. The implementation is based on traditional DRAGON(1)(2), one of the most well known floating point printing algorithm developed by Guy L. Steel, et al. I recently found another floating point printing library, google/double-conversion, which implements faster algorithm called Grisu(3).

This is an example using the google/double-conversion for Float#to_s.

1. Guy L. Steel, Jr and Jon L. White, How to Print Floating-Point Accurately, PLDI '90, http://dl.acm.org/ft_gateway.cfm?id=93559
2. Robert G. Burger and R. Kent Dybvig, Printing Floating-Point Numbers Quickly and Accurately, PLDI '96, http://www.cs.indiana.edu/~dyb/pubs/FP-Printing-PLDI96.pdf
3. Florian Loitsch, Printing Floating-Point Numbers Quickly and Accurately with Integers, PLDI '10, http://www.cs.tufts.edu/~nr/cs257/archive/florian-loitsch/printf.pdf

Grisu version is more than 4 times faster than DRAGON version, Float#to_s.

$ ruby -I lib test/benchmark.rb
🐉 Small float numbers, count=5000000, range=0.0...1.0
                           user     system      total        real
Float#to_s             4.500000   0.010000   4.510000 (  4.527218)
Float#hitokage_to_s    1.070000   0.000000   1.070000 (  1.083553)
Verifying results...👍

🐉 Usual float numbers, count=5000000, range=0.0...10000000.0
                           user     system      total        real
Float#to_s             4.650000   0.330000   4.980000 (  5.004367)
Float#hitokage_to_s    1.210000   0.140000   1.350000 (  1.364027)
Verifying results...👍

🐉 Big floats numbers, count=5000000, range=1.0e+20...1.0e+30
                           user     system      total        real
Float#to_s             6.050000   0.240000   6.290000 (  6.338893)
Float#hitokage_to_s    1.120000   0.000000   1.120000 (  1.132833)
Verifying results...👍

Add this line to your application's Gemfile:

gem 'hitokage'

And then execute:

$ bundle

Or install it yourself as:

$ gem install hitokage

It defines Float#hitokage_to_s.

require 'hitokage'
1.0.hitokage_to_s

Or, you can replace the default Float#to_s.

require 'hitokage/replace_float_to_s'
1.0.to_s

This library generates different string representation than Float#to_s for some values including 1e-10 and 1e10. However, the generated string can be converted to same float number using to_f.

After checking out the repo, run bin/setup to install dependencies. Then, run rake test to run the tests. You can also run bin/console for an interactive prompt that will allow you to experiment.

To install this gem onto your local machine, run bundle exec rake install. To release a new version, update the version number in version.rb, and then run bundle exec rake release, which will create a git tag for the version, push git commits and tags, and push the .gem file to rubygems.org.

Bug reports and pull requests are welcome on GitHub at https://github.com/[USERNAME]/hitokage.

The gem is available as open source under the terms of the MIT License.

The gem contains google/double-conversion.