Thread: exp: OVERFLOW error

The range for exp() when it's implemented as a double function will be about +/-700 for the input value.

If you can find/implement exp() as a long double, you may get about +/-11000 as the input to exp. But it seems like your compiler doesn't support this.

--
Mats

The only valid options are:
1. Write an arbitrary precision math library.
2. Find and use an arbitrary precision math library.
3. Use something other than C to solve your problem, Mathematica, Matlab to name a few.

Originally Posted by xuftugulus

The only valid options are:
1. Write an arbitrary precision math library.
2. Find and use an arbitrary precision math library.
3. Use something other than C to solve your problem, Mathematica, Matlab to name a few.

Well, I guess you can still use the expl() version if there is support for it on the system. I doubt finding a Borland version of "high precision library" may also be difficult.

--
Mats

I couldn't get my gcc-mingw to print a long double, but here's code that shows that LARGE numbers work fine with expl():

Code:

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

void printLongDouble(long double x)
{
  int e = 0;
  int m = 1;
  int c;
  int i;

  if (x < 0) {
      putchar('-');
      x = -x;
  }
  
  if (x > 100000.0) {
    while(x > 1.0) {
      e++;
      x /= 10.0;
    }
  }
  
  while (x < 0.00001) {
      e--;
      x *= 10;
  }
  while(m < x) m *= 10;
  do {
    c = (int)x / m;
    putchar((char)(c+'0'));
    x -= c * m;
    m /= 10;
  } while(x > 1.0);
  if (x) {
    putchar('.');
    m = 1;
    for(i = 0; x && i < 5; i++) {
      x *= 10;
      c = (int)x % 10;
      putchar((char)(c + '0'));
    }
  }
  if (e) 
    {
      if (e >= 0) c = '+'; 
      else { 
	c = '-'; 
	e = -e;
      }
      printf("E%c%d",c, e);
    }
  putchar('\n');
}

int main() {
  long double ld;
  double d;

  for(;;) {
    scanf("%lf", &d);
    
    ld = d;

    printLongDouble(expl(ld));
  }
  return 0;
}

Execution sample:

Code:

D:\temp>gcc -Wall exp.c

D:\temp>a
1000
0.19700E+435
9000
0.44703E+3909

--
Mats