Difference between revisions of "Bitwise Operations"

From Coder Merlin
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== Bitwise Operations ==
== 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.
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 ===
<pre>
<pre>
NOT 0111
NOT 0111
Line 10: Line 10:
   = 1000
   = 1000
</pre>
</pre>
 
{{Caution|Note that because zero bits are "flipped" to one bits the actual size of the word matters.  For example,
<pre>
NOT 0111
  = 1000
</pre>
when considering only a four-bit word, but in the case of an eight-bit word the correct answer would be:
<pre>
  = 1111 1000
</pre>
As such, it's usually best to left-pad the operand with zeroes before proceeding.  For example,
<pre>
NOT 0000 0111
  = 1111 1000
</pre>
}}
=== AND ===
The AND operation is useful for masking bits that are not interesting and then checking to see if a particular bit is set.
The AND operation is useful for masking bits that are not interesting and then checking to see if a particular bit is set.
<pre>
<pre>
     0101
     0101
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   = 0001
   = 0001
</pre>
</pre>
 
=== OR ===
<pre>
<pre>
   0101
   0101
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  = 0111
  = 0111
</pre>
</pre>
 
=== XOR ===
The XOR operation is useful for inverting selected bits:
The XOR operation is useful for inverting selected bits:
<pre>
<pre>
     0101
     0101

Revision as of 13:12, 29 September 2019

Within these castle walls be forged Mavens of Computer Science ...
— Merlin, The Coder

Prerequisites[edit]

Bitwise Operations[edit]

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[edit]

NOT 0111
————————
  = 1000
CautionWarnIcon.png
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[edit]

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[edit]

   0101
OR 0011
————————
 = 0111

XOR[edit]

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