From: Morton Goldberg <m_goldberg@...>
Date: 2007-08-30T14:28:11+09:00
Subject: Re: Bug in % (Float)?

On Aug 29, 2007, at 10:14 PM, Pe�a, Botp wrote:

> From: Charlie Lehardy [mailto:charlie.lehardy@gmail.com] :
> # irb(main):001:0> 1 % 0.1
> # => 0.1
> #
> # Shouldn't 1 % 0.1 be 0.0 and not 0.1?
>
> never trust floats in division :)
> ruby tries to be friendly at the expense of more surprises...
>
> irb(main):343:0> system "qri numeric.divmod | head -7"
> ---------------------------------------------------------  
> Numeric#divmod
>      num.divmod( aNumeric ) -> anArray
> ---------------------------------------------------------------------- 
> --
>      Returns an array containing the quotient and modulus obtained by
>      dividing num by aNumeric. If q, r = x.divmod(y), then
>
>          q = floor(float(x)/float(y)
>
> irb(main):345:0> 1.divmod 0.1
> => [9, 0.1]

If Numeric#divmod adhered to the above, the result would be [10.0,  
0.0], so the result is just plain wrong, not a matter of float  
inaccuracy. Proof:

x, y = 1.0, 0.1
(x/y).floor.to_f # => 10.0

> irb(main):347:0> 9*0.1+0.1
> => 1.0

Regards, Morton