[Bug c++/45542] std::pow(float) converts to double when compiled with -std=gnu++0x

[paolo dot carlini at oracle dot com]

--- Comment #1 from paolo dot carlini at oracle dot com  2010-09-05 12:42 
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There is nothing to fix here, see:

  http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#550


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paolo dot carlini at oracle dot com changed:

   What|Removed |Added

 Status|UNCONFIRMED |RESOLVED
 Resolution||INVALID


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=45542

[Bug c++/45542] std::pow(float) converts to double when compiled with -std=gnu++0x

[vincenzo dot innocente at cern dot ch]

--- Comment #2 from vincenzo dot innocente at cern dot ch  2010-09-05 13:09 
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Subject: Re:  std::pow(float) converts to double when compiled with
-std=gnu++0x

  Ciao Paolo,
On 5 Sep, 2010, at 2:42 PM, paolo dot carlini at oracle dot com wrote:

 
 
 --- Comment #1 from paolo dot carlini at oracle dot com  2010-09-05 12:42 
 ---
 There is nothing to fix here, see:
 
  http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#550
 
 
1) this is VERY unfortunate

2)
and then why
std::exp(float) invokes expf? (a well as all other transcendental and
trigonometric functions that invoke xyzf)
also
std::sqrt converts to sqrtss  
?

is this not a bit inconsistent?

  vincenzo



 -- 
 
 paolo dot carlini at oracle dot com changed:
 
   What|Removed |Added
 
 Status|UNCONFIRMED |RESOLVED
 Resolution||INVALID
 
 
 http://gcc.gnu.org/bugzilla/show_bug.cgi?id=45542
 
 --- You are receiving this mail because: ---
 You reported the bug, or are watching the reporter.


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=45542

[Bug c++/45542] std::pow(float) converts to double when compiled with -std=gnu++0x

[paolo dot carlini at oracle dot com]

--- Comment #3 from paolo dot carlini at oracle dot com  2010-09-05 15:36 
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The issue affects only mixed mode arithmetic (thus, functions taking at least
two arguments), and in that case, as Howard explained, C++0x does what Fortran
and C do. In any case, we are implementing correctly the FCD, for sure.


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=45542

[Bug c++/45542] std::pow(float) converts to double when compiled with -std=gnu++0x

[paolo dot carlini at oracle dot com]

--- Comment #4 from paolo dot carlini at oracle dot com  2010-09-05 16:15 
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By the way, if a function taking a single argument is passed and integer, the
return type is double, not float or long double and one can see that the
underlying mechanism is the same. All in all, I agreed with the resolution
suggested by Howard, at the time, and frankly I don't thick the DR should be
re-opened. CERN should send somebody to the ISO Meetings, like Fermilab does...


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=45542

[Bug c++/45542] std::pow(float) converts to double when compiled with -std=gnu++0x

[vincenzo dot innocente at cern dot ch]

--- Comment #5 from vincenzo dot innocente at cern dot ch  2010-09-05 19:55 
---
Subject: Re:  std::pow(float) converts to double when compiled with
-std=gnu++0x


On 5 Sep, 2010, at 6:15 PM, paolo dot carlini at oracle dot com wrote:

 
 
 --- Comment #4 from paolo dot carlini at oracle dot com  2010-09-05 16:15 
 ---
 By the way, if a function taking a single argument is passed and integer, the
 return type is double, not float or long double and one can see that the
 underlying mechanism is the same. All in all, I agreed with the resolution
 suggested by Howard, at the time, and frankly I don't thick the DR should be
 re-opened. CERN should send somebody to the ISO Meetings, like Fermilab does…

After reading the standard a couple of times,
I fully agree that gcc implements the standard as written including the last
resolution
to remove std::(T,int) (this last bit escaped my first reading)

I've discovered that std::pow(float,float) (called for instance as
std::pow(x,2.f))
behaves as I expect.

The fact that CERN is not represented in ISO is an old story (we are NOT
affiliated to any national committee)
and we rely on Fermilab representatives.

In any case this seems to be a C99 issue and my understanding is that C++ never
overrules C.

The conclusion is that we will have now to recommend to use pow(float,float)
not pow(float, int)
if float behavior is desired…


  vincenzo

 


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=45542

[Bug c++/45542] std::pow(float) converts to double when compiled with -std=gnu++0x

[paolo dot carlini at oracle dot com]

--- Comment #6 from paolo dot carlini at oracle dot com  2010-09-05 23:01 
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Ok... We can discuss these issues in better detail when we met. Well, remember
that this is Free Software, thus, if you are unsure about a behavior, just open
the header in an editor and look inside it: isn't only allowed, is encouraged!


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=45542