Class HashCode

CSharp/Clipper2Lib/HashCode.cs:53–129

  */

  public struct HashCode
  {
    private static readonly uint s_seed = GenerateGlobalSeed();

    // private const uint Prime1 = 2654435761U;
    private const uint Prime2 = 2246822519U;
    private const uint Prime3 = 3266489917U;
    private const uint Prime4 = 668265263U;
    private const uint Prime5 = 374761393U;

    private static uint GenerateGlobalSeed()
    {
      using RandomNumberGenerator randomNumberGenerator = RandomNumberGenerator.Create();
      byte[] data = new byte[sizeof(uint)];
      randomNumberGenerator.GetBytes(data);
      return BitConverter.ToUInt32(data, 0);
    }

    public static int Combine<T1, T2>(T1 value1, T2 value2)
    {
      uint hc1 = (uint) (value1?.GetHashCode() ?? 0);
      uint hc2 = (uint) (value2?.GetHashCode() ?? 0);

      uint hash = MixEmptyState();
      hash += 8;

      hash = QueueRound(hash, hc1);
      hash = QueueRound(hash, hc2);

      hash = MixFinal(hash);
      return (int) hash;
    }

    [MethodImpl(MethodImplOptions.AggressiveInlining)]
    private static uint QueueRound(uint hash, uint queuedValue)
    {
      return RotateLeft(hash + (queuedValue * Prime3), 17) * Prime4;
    }

    private static uint MixEmptyState()
    {
      return s_seed + Prime5;
    }

    [MethodImpl(MethodImplOptions.AggressiveInlining)]
    private static uint MixFinal(uint hash)
    {
      hash ^= hash >> 15;
      hash *= Prime2;
      hash ^= hash >> 13;
      hash *= Prime3;
      hash ^= hash >> 16;
      return hash;
    }

    [MethodImpl(MethodImplOptions.AggressiveInlining)]
    public static uint RotateLeft(uint value, int offset)
    {