/*
 * $Id: GN.c,v 1.3 2014/11/17 01:09:02 grog Exp $
 *
 * Compare guide numbers.
 *
 * Read in lines in format:
 *
 * Fraction    Aperture:tenths
 *
 * Aperture:tenths is the standard exposure meter format where a base aperture
 * is augmented by units of 0.1 EV.
 *
 * Output: Real aperture ("guide number"), calculated aperture, deviation.
 */
#include <math.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/file.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <unistd.h>

int main (int argc, char *argv [])
{
  int print_proportions = 0;			/* print deviations, not proportions */
  char fraction [10];
  float frac;					/* fraction as float */
  float base_aperture;				/* as represented in input */
  int aperture_fraction;			/* as represented in input */
  float aperture;				/* calculated from preceding 2 */
  float expected_aperture;			/* calculated from base reading */
  float aperture_difference;			/* difference between calculated and observed aperture */
  float base_gn = 1;				/* calculated from power == 1 */

  if (argc > 1)
    {
    if (strcmp (argv [1], "-p"))
      {
      fprintf (stderr, "Only option must be -p (print proportions, not deviations\n");
      exit (1);
      }
    print_proportions = 1;
    }
  printf ("Power  ratio\tRaw GN\tReal GN \tExpected  Deviation\n\n");
  while (scanf ("%s %f:%d\n", fraction, &base_aperture, &aperture_fraction) == 3)
    {
    aperture = base_aperture * pow (M_SQRT2, aperture_fraction / 10.);
    if (! strcmp (fraction, "1"))		/* 1 is special, should be first */
      {
      printf ("1\t1\t\%2.0f:%d\t%4.2f\n", base_aperture, aperture_fraction, aperture);
      base_gn = aperture;
      }
    else					/* fractional power */
      {
      frac = 1. / atof (&fraction [2]);		/* admire the error checking */
      expected_aperture = base_gn * sqrt (frac); /* this is what it should be */
      if (print_proportions)
	aperture_difference = pow (aperture, 2) / pow (expected_aperture, 2);
      else
	aperture_difference = pow (aperture, 2) / pow (expected_aperture, 2) - 1.;
      printf ("%s\t%6.5f\t %2.1f:%d \t%4.2f \t%4.2f \t%3.0f\n",
	      fraction,				/* as text */
	      frac,				/* numeric fraction */
	      base_aperture,
	      aperture_fraction,
	      aperture,
	      expected_aperture,
	      aperture_difference * 100.);
      }
    }
  return 0;
  }