Question

I have many objects in a matrix which are storing the connections to their neighbours in a single integer variable.

public static final int NONE = 0x00;
public static final int LEFT = 0x01;
public static final int TOP = 0x02;
public static final int RIGHT = 0x04;
public static final int BOTTOM = 0x08;

connections = LEFT | RIGHT | BOTTOM; // example usage

Now I want to be able to rotate certain objects by 90° CW or CCW. In the example above a clockwise rotation should be equivalent to

connections = TOP | BOTTOM | LEFT;

A left / right bitshift of 1 seems the obvious solution but I don’t know how to limit the bitshift to the bits of LEFT (0x01) to BOTTOM (0x08).

I hope someone can help me. I’m lost when it comes to bit operations.

Answer 1

This should do it:

connections = ((connections << 1) | (connections >> 3)) & 0x0f;