Tools.java

package de.blau.android.util.collections;

/**
 * Common methods
 */
class Tools {

	/** Taken from FastUtil implementation */

	/**
	 * Return the least power of two greater than or equal to the specified
	 * value.
	 *
	 * <p>
	 * Note that this function will return 1 when the argument is 0.
	 *
	 * @param x
	 *            a long integer smaller than or equal to 2<sup>62</sup>.
	 * @return the least power of two greater than or equal to the specified
	 *         value.
	 */
	private static long nextPowerOfTwo(long x) {
		if (x == 0)
			return 1;
		x--;
		x |= x >> 1;
		x |= x >> 2;
		x |= x >> 4;
		x |= x >> 8;
		x |= x >> 16;
		return (x | x >> 32) + 1;
	}

	/**
	 * Returns the least power of two smaller than or equal to 2<sup>30</sup>
	 * and larger than or equal to <code>Math.ceil( expected / f )</code>.
	 *
	 * @param expected
	 *            the expected number of elements in a hash table.
	 * @param f
	 *            the load factor.
	 * @return the minimum possible size for a backing array.
	 * @throws IllegalArgumentException
	 *             if the necessary size is larger than 2<sup>30</sup>.
	 */
	public static int arraySize(final int expected, final float f) {
		final long s = Math.max(2,
				nextPowerOfTwo((long) Math.ceil(expected / f)));
		if (s > (1 << 30))
			throw new IllegalArgumentException("Too large (" + expected
					+ " expected elements with load factor " + f + ")");
		return (int) s;
	}

	// taken from FastUtil
	private static final int INT_PHI = 0x9E3779B9;
	private static final long LONG_PHI = 0x9E3779B97F4A7C15L;

	public static int phiMix(final int x) {
		final int h = x * INT_PHI;
		return h ^ (h >> 16);
	}

	public static long phiMix(final long x) {
		long h = x * LONG_PHI;
		h ^= h >>> 32;
		return h ^ (h >>> 16);
	}

}