[Bug c++/31511] New: /usr/include/c++/bits/cmath.tcc: no match for ternary 'operator?:' in '((__n % 2u) != 0u) ? __x : 1'

[bav dot 272304 at gmail dot com]

It is known problem with GNU ISO C++ Library math implementation by Gabriel Dos
Reis.

g++ compiler says something like this:

/usr/include/c++/bits/cmath.tcc:41: error: no match for
ternary 'operator?:' in '((__n % 2u) != 0u) ? __x : 1'

It could be fixed by replacing the certain line at the cmath.tcc file

_Tp __y = __n % 2 ? __x : 1;

with more correct

_Tp __y = __n % 2 ? __x : _Tp(1);

(see cmath.tcc for details)

To reproduce error, try to pass to std::pow() std::complex object where T
isn't primitive type but some class with arithmetic operators overloaded.

I found it in g++ 3.3.5, g++ 4.0.0, etc.


-- 
   Summary: /usr/include/c++/bits/cmath.tcc: no match for ternary
'operator?:' in '((__n % 2u) != 0u) ? __x : 1'
   Product: gcc
   Version: 4.0.0
Status: UNCONFIRMED
  Severity: normal
  Priority: P3
 Component: c++
AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: bav dot 272304 at gmail dot com


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=31511

[Bug c++/31511] /usr/include/c++/bits/cmath.tcc: no match for ternary 'operator?:' in '((__n % 2u) != 0u) ? __x : 1'

[bav dot 272304 at gmail dot com]

--- Comment #2 from bav dot 272304 at gmail dot com  2007-04-08 21:16 
---
Code example:



#include 

template class Wrapper {
T x_;
public:
Wrapper () throw () : x_(0) {}
Wrapper (const T& x) throw () : x_(x) {}
Wrapper operator* (const Wrapper& x) const throw () {
return Wrapper (x_*x.x_);
}
Wrapper operator/ (const Wrapper& x) const throw () {
return Wrapper (x_/x.x_);
}
Wrapper operator+ (const Wrapper& x) const throw () {
return Wrapper (x_+x.x_);
}
Wrapper operator- (const Wrapper& x) const throw () {
return Wrapper (x_-x.x_);
}
Wrapper operator- () const throw () {
return Wrapper (-x_);
}
~Wrapper () throw () {}
};

int main () {

std::complex  > x (Wrapper(2.0));
std::pow (x, 23);

}



OUTPUT:

debian:/# g++ bug.cpp --pedantic --std=c++98 -Wall
/usr/include/c++/3.3/bits/cmath.tcc: In function `_Tp std::__cmath_power(_Tp,
   unsigned int) [with _Tp = std::complex >]':
/usr/include/c++/3.3/cmath:477:   instantiated from `_Tp std::__pow_helper(_Tp,
int) [with _Tp = std::complex >]'
/usr/include/c++/3.3/complex:564:   instantiated from `std::complex<_Tp>
std::pow(const std::complex<_Tp>&, int) [with _Tp = Wrapper]'
bug.cpp:29:   instantiated from here
/usr/include/c++/3.3/bits/cmath.tcc:42: error: no match for ternary
   'operator?:' in '((__n % 2) != 0) ? __x : 1'


-- 

bav dot 272304 at gmail dot com changed:

   What|Removed |Added
------------------------
 CC|    |bav dot 272304 at gmail dot
   ||com
  Component|libstdc++   |c++


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=31511

[Bug c++/31511] /usr/include/c++/bits/cmath.tcc: no match for ternary 'operator?:' in '((__n % 2u) != 0u) ? __x : 1'

[bav dot 272304 at gmail dot com]

--- Comment #3 from bav dot 272304 at gmail dot com  2007-04-08 21:17 
---
(In reply to comment #1)
> Gaby, not a big deal (complex is unspecified for T != floating, ...), but
> what do you think, shall we do the 1 -> _Tp(1) change?
> 

No, everything works if we fix this bug.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=31511

[Bug c++/31511] /usr/include/c++/bits/cmath.tcc: no match for ternary 'operator?:' in '((__n % 2u) != 0u) ? __x : 1'

[bav dot 272304 at gmail dot com]

--- Comment #5 from bav dot 272304 at gmail dot com  2007-04-08 21:21 
---
(In reply to comment #1)
> but what do you think, shall we do the 1 -> _Tp(1) change?

Change, please.


-- 

bav dot 272304 at gmail dot com changed:

   What|Removed |Added

  Component|libstdc++   |c++


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=31511