The maths library

On some target other it is possible to optionally link-in smaller libraries interfacing to the native ROM code. Such alternatives are normally slighlty weaker either in speed or precision but are still a good option when the program size becomes an issue.

The available options at the moment are:

The precision of an FP number is determined by the so called “EPSILON” value. It is the smallest value which can be added to '1' still making a difference.

The given example tests the pre-defined FLT_EPSILON constant and tries to determine EPSILON experimentally to compare the empiric results to the compiler's presets.

Compiler command line examples:

  zcc +<target> -lndos -create-app -lm epsilon.c

  zcc +zx -lndos -create-app -lmzx -DFASTMATH epsilon.c

#include <stdio.h>
#include <math.h>
#include <float.h>

#ifdef DOUBLE
double a,b;
#else
float a,b;
#endif

int exponent;


double getexp(double value) {
	exponent=0;
	while ((int)value==0.0) {
		exponent--;
		value *= 10.0;
	}
	return(value);
}



int main() {
  a=1;
  while ((1.0+a)!=1.0)
  {
	b=a;
	a=a/2.0;
  }
    
  putchar(12);
  getexp(b);
  printf ("Computed value for Epsilon:   %fe%d\n", getexp(b),exponent);
  if ((1.0+b)==1.0) {
	  printf ("..not confirmed.\n");
  }

  getexp(FLT_EPSILON);
  printf ("Predefined value for Epsilon: %fe%d\n", getexp(FLT_EPSILON),exponent);

  a=1.0;
  b=a;
  while ((a+FLT_EPSILON)>a) {
	b=a;
	a*=10.0;
  }
  a=b;
  if (a>1.0) {
	  while (((a+FLT_EPSILON)>a)&&(b!=a)) {
		b=a;
		/* if the loop stales, try adding a minimum value, FLT_EPSILON is fine */
		/* a+=1.0+FLT_EPSILON; */
		a+=1.0;
	  }
	  a=b;
  }
  

  if (a<10.0) {
	  printf ("FLT_EPSILON is very close to the real machine limit.\n");
  } else {
	  if (a>2000.0)
		printf ("FLT_EPSILON is far from the real machine limit.\n");
  }
  printf ("\nEPSILON is relevant for values <= %f\n", a);

  if ((1.0+FLT_EPSILON)==1.0) {
	  printf ("\nError: this value for FLT_EPSILON is not correct !\n\n");
  }

}