On Fri, 16 Jun 2000, Dave Peticolas wrote:
> Richard Wackerbarth writes:
> > On Fri, 16 Jun 2000, Dave Peticolas wrote:
> > > Ok, you've convinced me of the need to track 'smallest denominational
> > > units', but not why we need to use integers rather than FP numbers.
> > > You can round FP numbers, too. Why couldn't we just round the FP
> > > amounts to the appropriate precision when needed? If you're worried
> > > about the loss of accuracy, you should provide a realistic example
> > > where the precision of 64-bit floating points is insufficient.
> >
> > I don't have a problem with 64 bit FP precision. However, I worry that
> > you don't gain anything by using FP. And you do run the risk of
> > forgetting to process the values as money rather than true reals.
>
> The reason why I like doubles is that a huge amount of work has gone
> into making the IEEE floating point specification "correct". These
> quantities are used ubiquitously and are scrutinized by many people.
> I have great confidence that the calculations are being done
> correctly. OTOH, if we roll our own numerical library, I will have
> much less confidence. It's not that I think we are bad developers,
> it's just that the problem is quite complicated. It took a long time
> to get IEEE floating point correct, and there were some extremely
> smart people involved.
Unlike FP, Scaled integer arithmetic is easy. The main thing that we do is
addition. And that is the easiest to do.
Actually, the hard part is getting the rounding done in the right places.
A good FP package won't help there at all.
> For that reason, if we decide to drop doubles, I would rather use
> a library like gmp which has already been written/debugged rather
> than start from scratch. We've got too many other things to do.
I have no problem using gmp when Int64 is not available.
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