[PPL-devel] Problems with std::numeric_limits

[Roberto Bagnara]

Hi there,

we have been repeatedly bitten by std::numeric_limits because of its
default implementation, i.e., the one beginning with

   template<typename _Tp>
     struct numeric_limits : public __numeric_limits_base
     {
       /** The minimum finite value, or for floating types with
           denormalization, the minimum positive normalized value.  */
       static _Tp min() throw() { return static_cast<_Tp>(0); }
       /** The maximum finite value.  */
       static _Tp max() throw() { return static_cast<_Tp>(0); }
       /** The @e machine @e epsilon:  the difference between 1 and the least
           value greater than 1 that is representable.  */
       static _Tp epsilon() throw() { return static_cast<_Tp>(0); }
       ...

in the <limits> header file (I am looking at GCC version 4.0.2).

Is that default implementation mandated by the standard?
If so, well... fine.  But if it is not mandated then I think it makes
much sense to remove it as it seems a perfect recipe for disaster.

Another issue is: shouldn't, e.g., std::numeric_limits<int> and
std::numeric_limits<const int> be completely equivalent?
Here is a little C++ program demonstrating what I mean:

#include <limits>
#include <iostream>

using namespace std;

struct Foo {
   Foo(int) {
   };
   operator int() {
     return 27;
   }
};

int main() {
   std::cout << std::numeric_limits<Foo>::is_bounded << std::endl;
   std::cout << std::numeric_limits<Foo>::max() << std::endl;

   std::cout << std::numeric_limits<const int>::is_bounded << std::endl;
   std::cout << std::numeric_limits<const int>::max() << std::endl;

   std::cout << std::numeric_limits<int>::is_bounded << std::endl;
   std::cout << std::numeric_limits<int>::max() << std::endl;
}

Here it prints the following:

0
27
0
0
1
2147483647

All the best,

     Roberto

-- 
Prof. Roberto Bagnara
Computer Science Group
Department of Mathematics, University of Parma, Italy
http://www.cs.unipr.it/~bagnara/
mailto:bagnara at cs.unipr.it