Custom base conversion (to and from) (See related posts)

	private static final short BASE_40_RADIX = 40;
	private static final short BASE_40_BASE = 48;
	private static final String BASE_40_ZERO = "0";

	public static long fromBase40(char[] cs) {
		return fromBase(cs, BASE_40_BASE, BASE_40_RADIX);
	}

	public static char[] toBase40(final long i) {
		return toBase(i, BASE_40_BASE, BASE_40_RADIX, BASE_40_ZERO);
	}

	private static final short BASE_75_RADIX = 75;
	private static final short BASE_75_BASE = 48;
	private static final String BASE_75_ZERO = "0";

	public static long fromBase75(char[] cs) {
		return fromBase(cs, BASE_75_BASE, BASE_75_RADIX);
	}

	public static char[] toBase75(final long i) {
		return toBase(i, BASE_75_BASE, BASE_75_RADIX, BASE_75_ZERO);
	}

	private static final short BASE_90_RADIX = 90;
	private static final short BASE_90_BASE = 33;
	private static final String BASE_90_ZERO = "!";

	public static long fromBase90(char[] cs) {
		return fromBase(cs, BASE_90_BASE, BASE_90_RADIX);
	}

	public static char[] toBase90(final long i) {
		return toBase(i, BASE_90_BASE, BASE_90_RADIX, BASE_90_ZERO);
	}

	private static char[] toBase(final long i, final short base, final short radix, String nullCharacter) {
		long value = i;

		if (value == 0) {
			return nullCharacter.toCharArray();
		}

		String result = "";
		while (value > 0) {
			long mod = value % radix;
			value -= mod;
			if (value > 0) value /= radix;
			result = (char)(mod + base) + result;
		}

		return result.toCharArray();
	}

	private static long fromBase(char[] cs, final short base, final short radix) {
		long value = 0;
		for (int i = cs.length - 1; i >= 0; i--) {
			int digit = ((int)cs[i]) - base;
			if (digit < 0 || digit >= radix) {
				throw new IllegalArgumentException("Invalid Base" + radix + " character: " + cs[i]);
			}
			long digitBase = (long)Math.pow(radix, (cs.length - 1) - i);
			value = (digit * digitBase) + value;
		}

		return value;
	}

	public void testFromBase40() {
		assertEquals(2559999, NumberUtils.fromBase40("WWWW".toCharArray()));
		assertEquals(1117580, NumberUtils.fromBase40("ABCD".toCharArray()));

		assertEquals(0, NumberUtils.fromBase40("0".toCharArray()));
		assertEquals(1, NumberUtils.fromBase40("1".toCharArray()));

		assertEquals(40, NumberUtils.fromBase40("10".toCharArray()));
		assertEquals(80, NumberUtils.fromBase40("20".toCharArray()));

		assertEquals(41, NumberUtils.fromBase40("11".toCharArray()));
		assertEquals(81, NumberUtils.fromBase40("21".toCharArray()));

		assertEquals(81, NumberUtils.fromBase40("0021".toCharArray()));

		assertEquals(3061560805L, NumberUtils.fromBase40("MSTSD5".toCharArray()));
	}

	public void testToBase40() {
		assertEquals("0", new String(NumberUtils.toBase40(0)));
		assertEquals("1", new String(NumberUtils.toBase40(1)));

		assertEquals("10", new String(NumberUtils.toBase40(40)));
		assertEquals("20", new String(NumberUtils.toBase40(80)));

		assertEquals("11", new String(NumberUtils.toBase40(41)));
		assertEquals("21", new String(NumberUtils.toBase40(81)));

		assertEquals("ABCD", new String(NumberUtils.toBase40(1117580)));
		assertEquals("WWWW", new String(NumberUtils.toBase40(2559999)));

		assertEquals("MSTSD5", new String(NumberUtils.toBase40(3061560805L)));

	}

	public void testToBase90() throws Exception {
		assertEquals("#Q&Y.`QY#", new String(NumberUtils.toBase90(10908158098650842L)));
	}

	public void testFromBase90() throws Exception {
		assertEquals(10908158098650842L, NumberUtils.fromBase90("#Q&Y.`QY#".toCharArray()));
	}