V3 PATCH: numeric_limits<> support, fix PR/3865

[Roger Sayle]

On Tue, 3 Sep 2002, Richard Henderson wrote:
> On Tue, Sep 03, 2002 at 11:57:46AM -0600, Roger Sayle wrote:
> > bool has_snan = !(__builtin_snan("") == 0.0);
>
> If -fsignaling-nan, this ought to result in sigfpe.
> Thus you can't do that.

Is there any agreement on evaluating constant expressions containing
signaling NaNs at compile time.  I agree that if the above statement
where executed at run-time I'd expect a SIGFPE, but as an initializer
to a global constant?

> > Otherwise I agree that we might also need __builtin_has_snan{,f,l} to
> > determine whether we support signaling NaNs.
>
> There's two questions of "support".  (1) Can we represent the value,
> and (2) do we conserve signals.  I suspect that std::numeric_limits
> only cares about question 1, and not about question 2.

Good point.

Roger
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