private static int[] mix(int a, int b, int c) {
        a -= b; a -= c; a ^= (c >>> 13);
        b -= c; b -= a; b ^= (a << 8);
        c -= a; c -= b; c ^= (b >>> 13);
        a -= b; a -= c; a ^= (c >>> 12);
        b -= c; b -= a; b ^= (a << 16);
        c -= a; c -= b; c ^= (b >>> 5);
        a -= b; a -= c; a ^= (c >>> 3);
        b -= c; b -= a; b ^= (a << 10);
        c -= a; c -= b; c ^= (b >>> 15);

        return new int[]{ a, b, c };
    }
mix -- mix 3 32-bit values reversibly.
For every delta with one or two bits set, and the deltas of all three
high bits or all three low bits, whether the original value of a,b,c
is almost all zero or is uniformly distributed,
If mix() is run forward or backward, at least 32 bits in a,b,c
have at least 1/4 probability of changing.
If mix() is run forward, every bit of c will change between 1/3 and
2/3 of the time.  (Well, 22/100 and 78/100 for some 2-bit deltas.)
mix() was built out of 36 single-cycle latency instructions in a
structure that could supported 2x parallelism, like so:

<pre>
      a -= b;
      a -= c; x = (c&gt;&gt;13);
      b -= c; a ^= x;
      b -= a; x = (a&lt;&lt;8);
      c -= a; b ^= x;
      c -= b; x = (b&gt;&gt;13);
      ...
</pre>

<p>
Unfortunately, superscalar Pentiums and Sparcs can't take advantage
of that parallelism.  They've also turned some of those single-cycle
latency instructions into multi-cycle latency instructions.  Still,
this is the fastest good hash I could find.  There were about 2^^68
to choose from.  I only looked at a billion or so.
vespajlib/src/main/java/com/yahoo/collections/BobHash.java