Re: [boost] Proposed templated integer_sort

Subject: Re: [boost] Proposed templated integer_sort
From: Gevorg Voskanyan (v_gevorg_at_[hidden])
Date: 2008-12-16 12:36:33

Giovanni Piero Deretta wrote:

> To: boost_at_[hidden]
> Sent: Tuesday, December 16, 2008 7:19:52 PM
> Subject: Re: [boost] Proposed templated integer_sort
> 
> On Tue, Dec 16, 2008 at 3:03 PM, Pyry Jahkola wrote:
> > Gevorg Voskanyan wrote:
> >>
> >> I suggest modifying CastFloatIter() function to use memcpy for accessing
> >> floats as integers, as shown below:
> >
> > Hmm, I don't think it's any better than reinterpret casting.
> 
> Yes it is. It has the nice property of not leading to UB. And the
> result is well defined (the bitwise representation of the source is
> copied into the destination).
> 
> > (It actually does
> > the reinterpret cast when converting float const * to void const *...)
> 
> Not really.
> 
> >I'd
> > suggest using a union instead, for the purpose of treating a float as
> > integer:
> >
> >     template 
> >     inline To bitwise_cast(From const & from) {
> >         BOOST_STATIC_ASSERT(sizeof(To) == sizeof(From));
> >         union { To to; From from; } u;
> >         u.from = from;
> >         return u.to;
> >     }
> >
> 
> This is also undefined behavior even if it is explicitly supported by
> most compilers as an extension. It is not necessarily better than a
> memcpy and might actually be slower.
> 
> -- 
> gpd

Thanks Giovanni, I could not reply any better.

Best Regards,
Gevorg