The transform from x -y -z to x y z

[ronaldpan]

I cannot get the idea of these code. Could you please explain in detail:
// x -y -z -> x y z trans.bottomRightCorner<2, 1>() *= -1; trans.block<1, 2>(0, 1) *= -1; trans.bottomLeftCorner<2, 1>() *= -1;

In general, the reflection matrix or rotation 180 degree along x is : 1 0 0 0 -1 0 0 0 -1