/*
 * http://codegolf.stackexchange.com/q/54287/134
 * Reference implementation when invoked with two arguments,
 * transformation from / to Zeckendorf representation when invoked with
 * one argument.
 */

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

static const int
fibs[31] = {
	1, 2, 3, 5, 8, 13, 21, 34, 55, 89, 144, 233, 377, 610, 987, 1597, 2584,
	4181, 6765, 10946, 17711, 28657, 46368, 75025, 121393, 196418, 317811,
	514229, 832040, 1346269, 2178309
};


/* convert a number to Zeckendorf representation */
static int
tozeck(int n)
{
	int i, z = 0;

	for (i = 30; i >= 0; i--) {
		z <<= 1;

		if (n >= fibs[i]) {
			n -= fibs[i];
			z++;
		}
	}

	return z;
}

/* convert a number from Zeckendorf representation */
static int
unzeck(int z)
{
	int i, n = 0;

	for (i = 0; i < 31; i++)
		if (z & 1 << i)
			n += fibs[i];

	return n;
}

extern int
main(int argc, char *argv[])
{
	unsigned long a, b;
	char *endptr;

	switch (argc) {
	case 2:
		a = strtoul(argv[1], &endptr, 0);
		if (a > 2147483647 || *endptr != '\0' || *argv[1] == '\0')
			goto usage;

		if (a <= 3524577)
			printf("Z(%ld) = %d\n", a, tozeck(a));
		if ((a & a >> 1) == 0)
			printf("%ld = Z(%d)\n", a, unzeck(a));

		return EXIT_SUCCESS;

	case 3:
		a = strtoul(argv[1], &endptr, 0);
		if (a > 2147483647 || *endptr != '\0' || argv[1] == '\0' || (a & a >> 1)) {
			fprintf(stderr, "%s is not a valid Zeckendorf representation\n", argv[1]);
			return EXIT_FAILURE;
		}

		b = strtoul(argv[2], &endptr, 0);
		if (b > 2147483647 || *endptr != '\0' || argv[2] == '\0' || (b & b >> 1)) {
			fprintf(stderr, "%s is not a valid Zeckendorf representation\n", argv[2]);
			return EXIT_FAILURE;
		}

		a = unzeck(a);
		b = unzeck(b);
		if (a + b > 3524577) {
			fprintf(stderr, "Sum too large!\n");
			return EXIT_FAILURE;
		}

		printf("%d\n", tozeck(a + b));
		return EXIT_SUCCESS;

	default:
	usage:
		fprintf(stderr, "Usage: %s number or %s number number\n"
		    "numbers must be smaller than 2^31 = 1073741824\n"
		    "first case computes Zeckendorf representation and invers,\n"
		    "second case computes sum of numbers in Zeckendorf representaion.\n",
		    argv[0], argv[0]);
		return EXIT_FAILURE;
	}
}