From: Sean O'Dell <sean@...>
Date: 2004-05-13T02:27:38+09:00
Subject: Re: Major Addition Bug?

On Wednesday 12 May 2004 10:18, Dave Thomas wrote:
> On May 12, 2004, at 12:07, Sean O'Dell wrote:
> > On Wednesday 12 May 2004 09:53, ts wrote:
> >>>>>>> "S" == Sean O'Dell <sean@celsoft.com> writes:
> >>
> >> S> raise "false" if ((625.91 + 900.00 + 22.00) != 1547.91)
> >
> >   How old is this bug?  When is it
> > getting fixed?
>
> It's about 40 years old, and unlikely to be fixed. Floating point
> numbers are not represented exactly inside computers, and so floating
> point comparisons are routinely deprecated in books on programming.
> Certain values cannot ever be expressed in floating point
> representation.
>
> If you want exact, fractional, math, you should probably use the
> 'rational' library and investigate 'mathn'.

Funny though, if I set a variable to 1547.91 exactly, it is represented just 
fine.  A value during the arithmetic must be a value which can't be 
represented.

I had to massage my floating point math in C/C++ a lot many years ago, but I 
always assumed it was a flaw in the MS compiler, and once I got in the habit 
of doing it, I forgot about it.

Thanks for the info.  I'm far less bitter now about having to round the 
numbers for comparison.  =)

	Sean O'Dell