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Subject: Re: tr1::unordered_set<double> bizarre rounding behavior (x86)
From: Avi Kivity <avi@argo.co.il>
To: Gabriel Dos Reis <gdr@integrable-solutions.net>
Cc: gcc@gcc.gnu.org
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Date: Wed, 06 Jul 2005 12:38:00 -0000
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On Tue, 2005-07-05 at 20:05 +0200, Gabriel Dos Reis wrote:
> Paolo Carlin
> It is definitely a good thing to use the full bits of value
> representation if we ever want to make all "interesting" bits part of
> the hash value.  For reasonable or sane representations it suffices to
> get your hand on the object representation, e.g.:
> 
>    const int objsize = sizeof (double);
>    typedef unsigned char objrep_t[objsize];
>    double x = ....;
>    objrep_t& p = reintepret_cast<objrep_t&>(x);
>    // ...
> 
> and let frexp and friends only for less obvious value representation.

most architectures have different bit representations for +0.0 and -0.0,
yet the two values compare equal.