Have I written the macros correctly ?

[broli86]

Hi, I'm trying to write a macro for the relative difference function which is used to check the close enough floating point values. This is the relative difference function. I want to write a macro instead :

#define Abs(x)     ((x < 0 ? -(x) : (x))
#define Max(a,b) ((a) > (b) ? (a) : (b))

double reldif( double a, double b)
{
  double c = Abs(a);
  double d = Abs(b);

  d = Max(c,d);
  return d == 0.0 ? 0.0 : Abs(a-b)/d;
}


Then for checking equality of two floating points :
#define EPSILON 0.000001
.....
if ( reldif(a, b) <= TOLERANCE)

And here's my macro eq(a,b):

#define max(x, y) ((x) > (y) ?  (x) : (y)) 
#define eq(a, b)  max(fabs(a), fabs(b)) == 0.0 ? 0.0 : fabs(a - b) / (max(fabs(a), fabs(b)))

So we can simply write eq(a,b) <= EPSILON

can some one please tell me if this is correct or not ?

[C_ntua]

It seems so. Test them to be sure.

[foxman]

Well, have you tested it ?

As far as I see, it should be fine. But you should add an extra pair or two of paranthesis

#define eq(a, b)  (max(fabs(a), fabs(b)) == 0.0 ? 0.0 : fabs((a) - (b)) / (max(fabs(a), fabs(b))))

Personally I would stay with a normal function.

[broli86]

I have just tested them and it worked for all examples I took . I'm sometimes wary of using macros though because you never know whether it has gone wrong some place.