From: Charles Oliver Nutter <charles.nutter@...>
Date: 2009-02-15T19:04:44+09:00
Subject: [ruby-core:22140] Re: Confused about some code in mathn.rb

Charles Oliver Nutter wrote:
> Charles Oliver Nutter wrote:
>> In 1.8.6 and 1.8.7, these lines appear at line 202 in mathn.rb:
>>
>>       loop do
>>         if (neard**other.denominator == self.denominator)
>>           dem = neaed
>>           break
>>         end
>>       end
>>
>> I'm confused about the purpose of this code. If the equality check 
>> fails, it will simply loop forever. If the equality check passes, it 
>> will end after a single loop. So what's the purpose of the loop?
>>
>> Perhaps it never happens in MRI but for a particular spec running 
>> under JRuby it ends up comparing 3.999999999999999 with 4.0. I'm 
>> looking into whether we can tweak the power computation in JRuby to 
>> produce the 4.0 result, but it's still rather confusing what the code 
>> above is intended to do. Anyone?
> 
> More confusion in the same method...if I comment out the loop, it 
> continues on and blows up in trying to call num on self (a Rational). 
> But Rational does not define num, it defines numerator:
> 
> at line 208:
>       nearn = self.numerator.to_f ** (1.0/other.denominator.to_f)
>       Rational(num,den)
> 
> There is no definition of num or den as variables anywhere in the power2 
> method. I'm not sure how this method is supposed to work at all...

FWIW, this code seems to be the same on 1_8 branch. If I comment out the 
loop and replace Rational(num,den) with Rational(numerator,denominator) 
it seems to function, but obviously I'm still confused about why the 
loop is there at all.

- Charlie