expbrk.c

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

/**
 * expbrk.c 
 * generate exponential attack or decay breakpoint data
 */
int main(int argc, char** argv)
{
	int i, npoints;
	double startval, endval;
  double dur, step, start, end, currentstep;
	double fac, valrange, offset;
  const double verysmall = 1.0e-4; // ~-80dB. NB: this affects slope

	if (argc != 5) {
		fprintf(stderr, "Usage: expbrk duration npoints startval endval\n");
		return 1;
	}

  dur = atof(argv[1]);

	if (dur <= 0.0) {
		fprintf(stderr, "Error: duration must be positive.\n");
		return 1;
	}

	npoints = atoi(argv[2]);
	if (npoints <= 0) {
		fprintf(stderr, "Error: npoints must be positive!\n");
		return 1;
	}

	step = dur/npoints;

	startval = atof(argv[3]);
	endval = atof(argv[4]);    
	valrange = endval - startval;

	if (valrange == 0.0) {
		fprintf(stderr, "Warning: start and end values are the same!\n");
	}

	// initialize normalized exponential as attack or decay
  if (startval > endval) {
		start = 1.0;
		end = verysmall;
		valrange = -valrange;
		offset = endval;
	} else {
		start = verysmall;
		end = 1.0;
		offset = startval;
	}
	
  currentstep = 0.0;

  // make normalized curve, scale output to input values and range
  fac = pow(end/start, 1.0/npoints);

  for (i = 0; i < npoints; i++) {
		fprintf(stdout, "%.4lf\t%.8lf\n", currentstep, offset + (start * valrange));        
		start *= fac;
		currentstep += step;
  }

  // print final value
	fprintf(stdout, "%.4lf\t%.8lf\n", currentstep,offset + (start * valrange));
    
  fprintf(stderr, "done\n");
  return 0;
}