/*
 * Copyright © 2011 Nick Bowler
 *
 * License WTFPL2: Do What The Fuck You Want To Public License, version 2.
 * This is free software: you are free to do what the fuck you want to.
 * There is NO WARRANTY, to the extent permitted by law.
 */

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

const char *progname = "dpicalc";

static unsigned long
simple_strtoul(const char *str, const char *name, int base)
{
	unsigned long ret;
	char *end;

	errno = 0;
	ret = strtoul(str, &end, base);
	if (errno != 0) {
		fprintf(stderr, "%s: %s: invalid %s: %s\n",
		                progname, str, name, strerror(errno));
		exit(EXIT_FAILURE);
	} else if (*end != '\0') {
		fprintf(stderr, "%s: %s: invalid %s: trailing garbage\n",
		                progname, str, name);
		exit(EXIT_FAILURE);
	}

	return ret;
}

int main(int argc, char **argv)
{
	double diagonal, ratio, phys_width;
	unsigned long w, h;

	if (argc > 0)
		progname = argv[0];

	if (argc < 4) {
		fprintf(stderr, "usage: %s diagonal pixel_w pixel_h\n",
		                progname);
		return EXIT_FAILURE;
	}

	diagonal = strtod(argv[1], NULL);
	w = simple_strtoul(argv[2], "pixel width", 10);
	h = simple_strtoul(argv[3], "pixel height", 10);

	ratio = (double) h / w;
	if (!isnormal(ratio)) {
		fprintf(stderr, "%s: nonsensical aspect ratio (%.2f)\n",
		                progname, ratio);
	}

	phys_width = sqrt(diagonal*diagonal / (1 + ratio*ratio));
	printf("%.1f\n", w / phys_width);

	return 0;
}