Magic Cube

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// remember about the double cover or unit quaternions!

  private int mulQuat(int q1, int q2)

    {

    Static4D result = RubikSurfaceView.quatMultiply(QUATS[q1],QUATS[q2]);

    float rX = result.get0();

    float rY = result.get1();

    float rZ = result.get2();

    float rW = result.get3();

    final float MAX_ERROR = 0.1f;

    float dX,dY,dZ,dW;

    for(int i=0; i<QUATS.length; i++)

      {

      dX = QUATS[i].get0() - rX;

      dY = QUATS[i].get1() - rY;

      dZ = QUATS[i].get2() - rZ;

      dW = QUATS[i].get3() - rW;

      if( dX<MAX_ERROR && dX>-MAX_ERROR &&

          dY<MAX_ERROR && dY>-MAX_ERROR &&

          dZ<MAX_ERROR && dZ>-MAX_ERROR &&

          dW<MAX_ERROR && dW>-MAX_ERROR  ) return i;

      dX = QUATS[i].get0() + rX;

      dY = QUATS[i].get1() + rY;

      dZ = QUATS[i].get2() + rZ;

      dW = QUATS[i].get3() + rW;

      if( dX<MAX_ERROR && dX>-MAX_ERROR &&

          dY<MAX_ERROR && dY>-MAX_ERROR &&

          dZ<MAX_ERROR && dZ>-MAX_ERROR &&

          dW<MAX_ERROR && dW>-MAX_ERROR  ) return i;

      }

    return -1;

    }