Re: [IDEA+RFC] Possible solution for min()/max() war

["Peter T. Breuer" <ptb@it.uc3m.es>]

"A month of sundays ago Patrick J. LoPresti wrote:"
> This is a MUCH nicer solution.  max() is a well-defined mathematical
> concept; it is simply the larger of its two arguments, period.  It is
> C's *promotion* rules that kill you, especially signed->unsigned
> promotion.  So just forbid them, at least when they implicit.
> 
> You can argue about whether the "differing sizes" case should be a
> BUG(), since the output will still be mathematically correct.  It

To give you all something definite to look at, here's some test code:

// standard good 'ol faithful version
#define __MIN(x,y) ({\
   typeof(x) _x = x; \
   typeof(y) _y = y; \
   _x < _y ? _x : _y ; \
 })

// possible implemetation with type sanity checks - alter to taste
#define MIN(x,y) ({\
   const typeof(x) _x = ~(typeof(x))0; \
   const typeof(y) _y = ~(typeof(y))0; \
   void MIN_BUG(); \
   if (sizeof(_x) != sizeof(_y)) \
     MIN_BUG(); \
   if ((_x > 0 && _y < 0) || (_x < 0 && _y > 0)) \
     MIN_BUG(); \
   __MIN(x,y); \
 })

// test code that compiles with no complaints with -O1 -Wall
int main() {
  unsigned i = 1;
  unsigned j = -2;
  return MIN(i,j);
}

// test code that complains at link time (in this version) with ..
//  gcc -o test -O1 -Wall test.c
// /tmp/cczJbwv5.o: In function `main':
// /tmp/cczJbwv5.o(.text+0x7): undefined reference to `MIN_BUG'
// collect2: ld returned 1 exit status
//
int main() {
  unsigned i = 1;
  signed j = -2;
  return MIN(i,j);
}

> depends on how often it is useful to compare (say) unsigned chars
> against ints, and on whether the compiler warns about cases where you
> try to stuff the return value into a too-small container.  I bet that
> just forbidding signed->unsigned promotion would be enough.

Possibly. I have little clue as to the real extent of the problem.

Peter