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From Martin Sebor <se...@roguewave.com>
Subject Re: svn commit: r650902 - /stdcxx/trunk/src/num_put.cpp
Date Thu, 24 Apr 2008 05:52:41 GMT
Travis Vitek wrote:
>  

Thanks for the careful review!

> 
>> Eric Lemings wrote:
>>
>>
>>> -----Original Message-----
>>> From: faridz@apache.org [mailto:faridz@apache.org] 
>>>
>>> Author: faridz
>>> Date: Wed Apr 23 08:20:07 2008
>>> New Revision: 650902
>>>
>>> URL: http://svn.apache.org/viewvc?rev=650902&view=rev
>>> Log:
>>> 2008-04-23 Farid Zaripov <farid_zaripov@epam.com>
>>>
>>> 	STDCXX-880	
>>> 	* src/num_put.cpp: Added simple overloads of the 
>>> 	__rw_isfinite(), __rw_signbit(), __rw_isinf(),
>>> 	__rw_isnan(), __rw_isqnan(), __rw_issnan()
>>> 	for float and long double types.
>>>
>>> Modified:
>>>     stdcxx/trunk/src/num_put.cpp
>>>
>>
>> With just a quick review, this change looks a bit suspicious.  The
>> respective overloads for type double are all defined within
>> conditional-compile directives.  It follows that float and long double
>> overloads would be defined similarly unless I'm missing something.
>>
> 
> The overloads on double are in platform specific #ifdef blocks because
> they have platform specific code in them (_finite, finite, isfinite). At
> least that is the only reason I see for it. So I don't really see the
> overloads on float and double outside of platform specific blocks as a
> problem as there is no platform specific code in them.

I guess I don't understand why the float overloads are all
unconditionally hardcoded:
http://fisheye6.cenqua.com/browse/stdcxx/trunk/src/num_put.cpp?r=trunk#l184

> 
> I'm more worried about why the overloads on float and long double are
> added at all. If they are only being called from __rw_fmat_infinite(),
> and that function only works with a double, then I see no motivation for
> the overloads.

Hmm. I thought Farid was saying __rw_fmat_infinite() was only being
called with a double argument. It looks like it's potentially called
with all three floating point arguments except the __rw_isfinite()
function is hardcoded for float and long double to return false so
__rw_fmat_infinite() is only called for doubles. So he was right,
but the way it's done seems very confusing. Why do we bother to call
__rw_isfinite(float) and __rw_isfinite(long double) at all when we
know that they're hardcoded to return true?

> 
> I'm also wondering why we provide default implementations of these
> functions if we know good and well that the results are wrong (for
> platforms that don't define _WIN32, _RWSTD_OS_SUNOS, or fpclassify).
> Shouldn't we fail to compile in this case?

My understanding is that the defaults will make the facet fall
back on using sprintf(). Farid, can you confirm that? (I don't
think we should ever fail to compile this code as long we have
sprintf to fall back on).

> 
> The other thing that freaks me out is the implementation of __rw_signbit
> on platforms defining _RWSTD_OS_SUNOS. It assumes something similar to
> IEEE-745 double representation. This may be a safe assumption for the
> time being, but what happens if the user compiles with -fnonstd? Does
> this still work?

It should although I haven't tried it. The bit pattern doesn't
change. (FWIW, I'm responsible for the function on Solaris).
Here's the documentation for reference:
http://docs.sun.com/app/docs/doc/819-5265/bjapp?a=view#bjarb

Martin

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