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With inspiration from other libraries

There is a newer version: 2.12.15

package io.virtdata.libbasics.shared.from_long.to_long;

import org.greenrobot.essentials.hash.Murmur3F;
import io.virtdata.annotations.ThreadSafeMapper;

import java.nio.ByteBuffer;
import java.util.function.LongUnaryOperator;

/**
 * This uses the Murmur3F (64-bit optimized) version of Murmur3,
 * not as a checksum, but as a simple hash. It doesn't bother
 * pushing the high-64 bits of input, since it only uses the lower
 * 64 bits of output.
 *
 * Unlike the other hash functions, this one may return positive
 * as well as negative values.
 */
@ThreadSafeMapper
public class SignedHash implements LongUnaryOperator {

    // TODO: Bench this against the non-state based TL implementations
    private ThreadLocal state_TL = ThreadLocal.withInitial(State::new);

    @Override
    public long applyAsLong(long value) {
        State state = state_TL.get();
        state.murmur3F.reset();
        state.bb.putLong(0,value);
        state.murmur3F.update(state.bb.array(),0,Long.BYTES);
        long result= state.murmur3F.getValue();
        return result;
    }

    private static class State {
        public ByteBuffer bb = ByteBuffer.allocate(Long.BYTES);
        public Murmur3F murmur3F = new Murmur3F();
    }
}