Bitwise Operations

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Curriculum

Coder Merlin™  Computer Science Curriculum Data

Unit: Boolean algebra Experience Name: Bitwise Operations (W1015) Next Experience: () Knowledge and skills: §10.326 Demonstrate understanding and proficiency in the use of bitwise operations Topic areas: Boolean algebra Classroom time (average): 10 minutes Study time (average): 60 minutes Successful completion requires knowledge: understand the use of bitwise operations with common Boolean operators Successful completion requires skills: demonstrate proficiency in using bitwise operations with common Boolean operators

Bitwise Operations

A bitwise operation operates on one or more bit patterns at the level of their individual bits. It is a fast, simple action supported by the ALU (Arithmetic Logic Unit) and is used to manipulate values for comparisons and calculations. The normal operation is simply applied bit by bit.

NOT

NOT 0111
————————
  = 1000

Caution

Note that because zero bits are "flipped" to one bits the actual size of the word matters. For example,

NOT 0111
  = 1000

when considering only a four-bit word, but in the case of an eight-bit word the correct answer would be:

  = 1111 1000

As such, it's usually best to left-pad the operand with zeroes before proceeding. For example,

NOT 0000 0111
  = 1111 1000

AND

The AND operation is useful for masking bits that are not interesting and then checking to see if a particular bit is set.

    0101
AND 0011
————————
  = 0001

OR

   0101
OR 0011
————————
 = 0111

XOR

The XOR operation is useful for inverting selected bits:

    0101
XOR 0011
————————
  = 0110

Because of this property, XOR is sometimes used to clear a register (to zero) by XOR’ing it with itself. In some cases this can be much faster than explicitly loading the value of 0.

    1010
XOR 1010
————————
  = 0000