Date: Sat, 19 Apr 2003 10:23:38 +0200
From: "Eli Zaretskii" <eliz AT elta DOT co DOT il>
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To: ams AT ludd DOT luth DOT se
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	(ams AT ludd DOT luth DOT se)
Subject: Re: Long double confusion
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> From: <ams AT ludd DOT luth DOT se>
> Date: Thu, 17 Apr 2003 19:03:00 +0200 (CEST)
> 
> My readings on the net doesn't show what a long double with it
> exponent set to 0x7fff and a _cleared_ most significant bit in the
> mantissa is. The most significant bit for a long double is the
> integer bit (which isn't present in floats or doubles).
> 
> As far as I understand a long double with exponent == 0 and with
> the most significant bit in the mantissa cleared is a denormal (which
> isn't a NaN but a value close to 0).
> 
> But I don't know what to make of it when exponent != 0.
> 
> Are they all NaNs? Only the ones with exponent == 0x7fff? Or none of
> them?

See section 7.4.4 of the Intel Manual: it calls those numbers
"unnormals".

Such numbers are generally a result of interpreting arbitrary bit
patterns as FP numbers (a.k.a. "bugs").

IIRC, our _doprnt has special support for those.