/*
 * Calculate a rough approximation of any factorial. Fast!
 *
 * To see how it works, take the decadic logarithm of any decimal number,
 * split it up by the digits before and after the decimal point, and examine
 * both numbers. Then, take the logarithm of a generic factorial and see what
 * happens.
 * "nachkomma" and "vorkomma" are the german words for the digits after and
 * before the decimal point, respectively. Because I don't know their english
 * words (postpoint and prepoint?), I left them as they are.
 *
 * Give any integer number on the command line ...
 *
 *                                                       Frank Pilhofer, 1995
 *                                                                  fp@fpx.de 
 *
 * Copy freely with this message intact.
 */

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

int
main (int argc, char *argv[])
{
  double nachkomma;
  long   zahl, iter, vorkomma;

  zahl      = atol (argv[1]);
  vorkomma  = 0L;
  nachkomma = 0.0;
  
  for (iter=1; iter<=zahl; iter++) {
        vorkomma += (long) floor (log10 ((double) iter));
        nachkomma+=        fmod  (log10 ((double) iter), 1.0);

        if (nachkomma >= 1) {
                vorkomma += 1L;
                nachkomma-= 1.0;
                }
        }

  printf ("Result: %ld! = %lf * 10^%ld\n", zahl, pow (10, nachkomma), vorkomma);
  return 0;
}