Re: signed is undefined and has been since 1992 (in GCC)

[Michael Veksler]

Robert Dewar wrote on 28/06/2005 22:20:56:

> I am puzzled, why would *ANYONE* who knows C use int
> rather than unsigned if they want wrap around semantics?
>

int saturated_mul(int a, int b)
{
   int ret= a*b;
   if (a == 0 || ret % a == 0)
      return ret;
   else if ( (a<0) == (b<0) ) // same sign
      return MAX_INT;
   else
      return MIN_INT;
}

instead of the bizzare:
int saturated_mul(int a, int b)
{
   // (unsigned)a*b does not give easy ways to
   // find signed overflow on negatives

   if (a==0 || b==0)
      return 0;

   bool positive = ( (a<0) == (b<0) );
   if (positive)
   {
       unsigned u_a=a, u_b=b;
       if (a < 0)
       {
           u_a *= -1;
           u_b *= -1;
       }
       unsigned ret= u_a*u_b;
       if (ret % u_a == 0)
         return ret;
       else
         return MAX_INT;
   }
   else
   {
     // negative
     even more bizzare code;
   }

It would be really great the standard could
make my life easier. I need to code to standard,
not to gcc, so extending gcc may not help....

  Michael