From: Dominik Bathon <dbatml@...>
Date: 2006-02-19T03:41:36+09:00
Subject: Re: patch for rational.rb (gcd)

On Sat, 18 Feb 2006 18:42:03 +0100, Mathieu Bouchard <matju@artengine.ca>  
wrote:

> On Sun, 19 Feb 2006, Dominik Bathon wrote:
>
>> $ ruby gcd_bench.rb
>>       user     system      total        real
>> gcd  0.390000   0.000000   0.390000 (  0.390554)
>> gcd2  6.410000   0.030000   6.440000 (  6.469019)
>> gcd3  0.170000   0.000000   0.170000 (  0.168139)
>> gcd4  0.120000   0.000000   0.120000 (  0.122690)
>
> What's differing in versions of Ruby so that the difference in execution
> times between gcd2 and gcd3 is either nothing or huge?

ruby-1.9's mathn.rb does already have the euclid gcd in mathn.rb:

class Integer

   remove_method(:gcd2)
   def gcd2(other)
     min = self.abs
     max = other.abs
     min, max = max % min, min while min > 0
     max
   end


while 1.8.4's mathn.rb doesn't:

class Integer

   def gcd2(int)
     a = self.abs
     b = int.abs
     a, b = b, a if a < b

     pd_a = a.prime_division
     pd_b = b.prime_division

     gcd = 1
     for pair in pd_a
       as = pd_b.assoc(pair[0])
       if as
	gcd *= as[0] ** [as[1], pair[1]].min
       end
     end
     return gcd
   end


So the new implementation obviously has already been merged, just not in  
1.8.

Dominik