Re: [Chicken-hackers] CR: Division by inexact zero should return infinity/nan

[Peter Bex]

On Thu, Aug 25, 2011 at 03:50:40AM -0400, Felix wrote:
> > This is really annoying, as you'd get "random" errors when you're working
> > with numbers in the extreme ranges representable by flonums even if you
> > absolutely know you're dividing by nonzero values.
> 
> Yes, that's floating point.

No, that's the division operator in Chicken.  The particular floating
point representation we are using explicitly supports returning infinities.

> > All other Schemes I tested with (Guile, Gauche, Scheme48, Racket and Gambit)
> > return +inf.0 for (/ 1.0 0.0) and -inf.0 for (/ -1.0 0.0).
> > They return +nan.0 for (/ 0.0 0.0).  Extra data points would be welcome.
> 
> CL signals div-by-zero.

But we're a Scheme.  Also, CL is overengineered design by committee
and hence is and not tied to the IEEE standard (it's optional).
According to the Hyperspec, this is actually not even defined; it says
an implementation *might* raise an error on zero.  Returning inf or nan
is allowed too.  I guess your favorite implementation just doesn't.

We are, since we compile to C, which (AFAIK) is explicitly tied to IEEE
floating point representation and semantics.  At least, it is on modern
machines.  We're already using it everywhere (except in the division case)

Cheers,
Peter
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