23. Binary Masks

• Logical operations can be used to apply masks to bit patterns.

• The masks are used when there is a need to set some bit positions to 1 or to 0.

• Only specified bit positions are updated, while other bits are ignored...

  • ...hence the technical term, bit mask.

• A typical use of masks is:

  • Use (X OR 1) to set X bit to 1

  • Use (X OR 0) to leave X bit unchanged

  • Use (X AND 0) to set X bit to 0

  • Use (X AND 1) to leave X bit unchanged