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package au.csiro.variantspark.utils;

import com.google.common.primitives.Ints;
import com.google.common.primitives.Longs;

/**
 * A helper class for fast MumMur3 calculation with changing seed based directly on 
 * [[com.google.common.hash.Murmur3_32HashFunction]] (from guava)
 */
public final class MurMur3Hash {
	private static final int C1 = 0xcc9e2d51;
	private static final int C2 = 0x1b873593;

	public static int hashInt(int input, int seed) {
		int k1 = mixK1(input);
		int h1 = mixH1(seed, k1);

		return fmix(h1, Ints.BYTES);
	}

	public static int hashLong(long input, int seed) {
		int low = (int) input;
		int high = (int) (input >>> 32);

		int k1 = mixK1(low);
		int h1 = mixH1(seed, k1);

		k1 = mixK1(high);
		h1 = mixH1(h1, k1);

		return fmix(h1, Longs.BYTES);
	}

	private static int mixK1(int k1) {
		k1 *= C1;
		k1 = Integer.rotateLeft(k1, 15);
		k1 *= C2;
		return k1;
	}

	private static int mixH1(int h1, int k1) {
		h1 ^= k1;
		h1 = Integer.rotateLeft(h1, 13);
		h1 = h1 * 5 + 0xe6546b64;
		return h1;
	}

	// Finalization mix - force all bits of a hash block to avalanche
	private static int fmix(int h1, int length) {
		h1 ^= length;
		h1 ^= h1 >>> 16;
		h1 *= 0x85ebca6b;
		h1 ^= h1 >>> 13;
		h1 *= 0xc2b2ae35;
		h1 ^= h1 >>> 16;
		return h1;
	}
}