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Re: strtod ("nan") returns negative NaN
On Wed, 15 Aug 2018, Paul Koning wrote:
> > * Different processors have different preferences for what a "default"
> > quiet NaN (e.g. one produced by an operation without NaN operands) should
> > look like. Some clear all the lower mantissa bits, some set them. If you
> > use the built-in functions then you generate NaNs following GCC's
> > knowledge of such processor conventions.
>
> But does that matter? It should be sufficient to generate a legal NaN
> when one is requested. Given that there are don't care bits in the
> representation of NaN, it might look different from one generated by the
> hardware as the output of some operation, but a NaN is a Nan so long as
> it matches what the spec says -- right?
Well, it mattered enough for ARM to send a patch to the NaN bits set in
ARM glibc fma
<https://sourceware.org/ml/libc-alpha/2014-02/msg00740.html>.
--
Joseph S. Myers
joseph@codesourcery.com