Ruby Core Performance Patch: Fixnum#gcd

See the attached patch.

Much Love to Ruby,
Kurt Stephens

=======================================================

Date uses Rational heavily, which calls Integer#gcd for every new Rational.
The Integer#gcd method is generic to handle Bignums,
but performs terribly for Fixnum#gcd(Fixnum),
which is probably the most often case.

This hack saved 15% execution time in a large Rails application.

See http://kurtstephens.com/node/34

=======================
# fixnum_gcd_test.rb

require 'benchmark'
require 'rational'

srand(1212398)

args = (0...10000).map do | x |
  [ rand(100000), rand(100000) ]
end
# puts args.inspect

Benchmark.bmbm do | bm |
  bm.report("Fixnum#gcd") do
    100.times do
      args.each do | x, y |
        x.gcd(y)
      end
    end
  end
end

=======================

 > ruby-trunk/ruby fixnum_gcd_test.rb
Rehearsal ----------------------------------------------
Fixnum#gcd   1.160000   0.000000   1.160000 (  1.191571)
------------------------------------- total: 1.160000sec

                 user     system      total        real
Fixnum#gcd   1.160000   0.010000   1.170000 (  1.203422)

 > ruby-trunk-orig/ruby fixnum_gcd_test.rb
Rehearsal ----------------------------------------------
Fixnum#gcd   3.980000   0.000000   3.980000 (  4.089624)
------------------------------------- total: 3.980000sec

                 user     system      total        real
Fixnum#gcd   3.960000   0.000000   3.960000 (  4.031807)