Proposal for Intermediate Challenge #117 with Bonus 2. Unreliable for date before 1st January 1970.

MayaLongCount.java

package fr.daniel.maya;

import java.util.Calendar;

public class MayaLongCount {

	public static String convertTo(int year, int month, int date) {
		Calendar calendar = Calendar.getInstance();
		calendar.set(year, month - 1, date);
		long day = calendar.getTimeInMillis() / 86_400_000;

		long baktun = day / 144_000 + 12;
		day %= 144_000;
		
		long katun = day / 7_200 + 17;
		day %= 7_200;

		long tun = day / 360 + 16 ;
		day %= 360;

		long uinal = day / 20 + 7;

		long kin = day % 20 + 5;

		if (kin >= 20) {
			kin -= 20;
			uinal++;
		}
		if (uinal >= 18) {
			uinal -=  18;
			tun++;
		}
		if (tun >= 20) {
			tun -= 20;
			katun++;
		}
		if (katun >= 20) {
			katun -= 20;
			baktun++;
		}

		return String.format("%d.%d.%d.%d.%d", baktun, katun, tun, uinal, kin);
	}

	public static String convertFrom(int baktun, int katun, int tun, int uinal, int kin) {
		baktun -= 12;
		katun -= 17;
		tun -= 16;
		uinal -= 7;
		kin -= 5;

		long day = baktun * 144_000 + katun * 7_200 + tun * 360 + uinal * 20 + kin;

		Calendar calendar = Calendar.getInstance();

		calendar.setTimeInMillis(day * 86_400_000);

		return String.format("%d/%d/%d", calendar.get(Calendar.DAY_OF_MONTH), calendar.get(Calendar.MONTH) + 1, calendar.get(Calendar.YEAR));
	}

	/**
	 * @param args
	 */
	public static void main(String[] args) {
		System.out.println(convertTo(1970, 1, 1));
		System.out.println(convertTo(1988, 7, 20));
		System.out.println(convertTo(2012, 12, 12));
		System.out.println(convertTo(2012, 12, 21));

		System.out.println(convertFrom(12, 17, 16, 7, 5));
		System.out.println(convertFrom(13, 0, 0, 0, 0));
		System.out.println(convertFrom(14, 0, 0, 0, 0));
	}

}