Difference between revisions of "Bitwise Operations"
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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
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
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