/* "Smart" printer using imperial/metric units
 *  depending on what can be written in fewer
 *  significant digits
 *
 *  by Andrew Poelstra, April 2011, no copyright
 *  */



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

/* Appears to work with N_DIGITS set to 10; i.e.,
 * it correctly sees that .3240000001 needs all 10
 * digits, while adding an extra zero drops it down
 * to three. */
#define N_DIGITS	10
int min_sig_figs(double d)
{
  int stack[N_DIGITS] = {0};
  int idx = 0;
  int sum = 0, sum2 = 0, count = 0;

  if(d == 0) return 0;

  /* Normalize to x.xxxx... form */
  if(d < 0)      d *= -1;
  while(d >= 10) d /= 10;
  while(d < 1)   d *= 10;

  /* Load digits into stack */
  for(idx = 0; idx < N_DIGITS; ++idx)
    {
      stack[idx] = floor(d + 1e-5);
      d = (d - stack[idx]) * 10;
      sum += stack[idx];
    }
  /* Determine how many digits were actually needed */
  for(idx = 0; sum2 < sum; ++idx)
    {
      sum2 += stack[idx];
      ++count;
    }
  
  return count;
}

/* Converts a measurement to a string, with units,
 * choosing metric/imperial to use least sig.figs. */
char *CoordToString(double nanos)
{
  static char buff[255];
  int b_units_mm = 0;
  const char *units;

  if(min_sig_figs(nanos) < min_sig_figs(nanos / 254.0))
    b_units_mm = 1;

  if(b_units_mm)
    {
      nanos /= 1000000;
      units  = "mm";
      if(nanos < 0.00001)
        {
          nanos *= 1000000;
          units  = "nm";
        }
      if(nanos < 0.01)
        {
          nanos *= 1000;
          units  = "um";
        }
    }
  else
    {
      nanos /= 25400;
      units  = "mil";
      if(nanos < 0.00001)
        {
          nanos *= 1000000;
          units  = "umil";
        }
      if(nanos < 0.01)
        {
          nanos *= 1000;
          units  = "mmil";
        }
      if(nanos < 0.1)
        {
          nanos *= 100;
          units  = "cmil";
        }
    }

  sprintf(buff, "%.2f%s", nanos, units);
  return buff;
}


/* TEST DRIVER */
int main(void)
{
  double d;

  for(d = 127; d < 500; d += 12.7)
    printf("Inputted %s.\n", CoordToString(d));

  return 0;
}