[Bug c/17645] Add a warning for potentially unsafe unsigned operations

[mathieu at malaterre dot com]

------- Additional Comments From mathieu at malaterre dot com  2005-07-06 03:00 
-------
Using gcc --version:
g++ (GCC) 4.1.0 20050607 (experimental)

I can still reproduce the same unsafe operation:

#include <iostream>

int main()
{
  unsigned int l = (unsigned int)-1;
  const int a = l/2;
  const int b = l/2+1;
  const double t = 0.5;
  const int c = a + t * (b -a);
  std::cout << "c=" << c << std::endl;
  const int d = (1.0 - t) * a + t * b;
  std::cout << "d=" << d << std::endl;

  return 0;
}

$ /usr/lib/gcc-snapshot/bin/g++ -O3 -ftrapv test.c
$  ./a.out                                                                     
                                           
c=2147483647
d=0


I cannot seems to find a way to generate traps on overflow.

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
          Component|c++                         |c


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=17645