Difference between revisions of "Not"
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− | < | + | The unary operator <syntaxhighlight lang="pascal" enclose="none">not</syntaxhighlight> negates a Boolean value. |
− | < | + | [[FPC]] also knows the bitwise <syntaxhighlight lang="pascal" enclose="none">not</syntaxhighlight> when supplied with an ordinal type. |
− | + | <syntaxhighlight lang="pascal" enclose="none">not</syntaxhighlight> is a reserved word. | |
+ | |||
== Boolean operation == | == Boolean operation == | ||
+ | The operator <syntaxhighlight lang="pascal" enclose="none">not</syntaxhighlight> represent the logical negation <math>\neg A</math>. | ||
+ | In electrical engineering one might write <math>-A</math> or <math>\overline{A}</math> instead, however the unary [[Minus|minus sign]] has a different meaning in programming. | ||
− | + | {| class="wikitable" style="text-align:center; margin:auto;" | |
− | + | ! <syntaxhighlight lang="pascal" enclose="none">A</syntaxhighlight> | |
− | === | + | ! <syntaxhighlight lang="pascal" enclose="none">not A</syntaxhighlight> |
− | |||
− | |||
|- | |- | ||
− | + | | <syntaxhighlight lang="pascal" enclose="none">false</syntaxhighlight> | |
+ | | style="background: #eeeeee" | <syntaxhighlight lang="pascal" enclose="none">true</syntaxhighlight> | ||
|- | |- | ||
− | | | + | | <syntaxhighlight lang="pascal" enclose="none">true</syntaxhighlight> |
− | + | | style="background: #eeeeee" | <syntaxhighlight lang="pascal" enclose="none">false</syntaxhighlight> | |
− | + | |+ truth table for logical negation | |
− | |||
− | |style="background: #eeeeee" | | ||
|} | |} | ||
+ | <syntaxhighlight lang="pascal" enclose="none">not</syntaxhighlight> has the highest precedence among logical operators. | ||
− | == | + | == bitwise operation == |
− | + | The bitwise <syntaxhighlight lang="pascal" enclose="none">not</syntaxhighlight> flips every bit in an ordinal type. | |
− | + | not 1100'1010 | |
− | + | ――――――――――――― | |
− | == | + | 0011'0101 |
− | + | It effectively calculates the one's complement. | |
− | <syntaxhighlight> | + | On virtually all platforms it is implemented by the <syntaxhighlight lang="asm" enclose="none">not</syntaxhighlight> instruction. |
− | + | On NAND-gate-based architectures the <syntaxhighlight lang="asm" enclose="none">not</syntaxhighlight> instruction can be calculated by the expression <math>A \barwedge (111…111)_2</math>. | |
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− | </syntaxhighlight> | ||
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− | <syntaxhighlight> | ||
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− | </ | ||
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− | == | + | Note, that only <syntaxhighlight lang="pascal" enclose="none">not %0</syntaxhighlight> will definitely result in a value interpretable as <syntaxhighlight lang="pascal" enclose="none">true</syntaxhighlight>. |
− | + | However, not every <syntaxhighlight lang="pascal" enclose="none">not x</syntaxhighlight> will result in a value interpretable as <syntaxhighlight lang="pascal" enclose="none">false</syntaxhighlight>, since only <syntaxhighlight lang="pascal" enclose="none">0</syntaxhighlight> is considered as <syntaxhighlight lang="pascal" enclose="none">false</syntaxhighlight> and every other value as <syntaxhighlight lang="pascal" enclose="none">true</syntaxhighlight>. | |
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− | + | == see also == | |
+ | * {{Doc|package=RTL|unit=system|identifier=.op-logicalnot-variant-ariant|text=<syntaxhighlight lang="pascal" enclose="none">system.logicalNot</syntaxhighlight>}} |
Revision as of 02:01, 7 November 2018
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The unary operator not
negates a Boolean value.
FPC also knows the bitwise not
when supplied with an ordinal type.
not
is a reserved word.
Boolean operation
The operator not
represent the logical negation [math]\displaystyle{ \neg A }[/math].
In electrical engineering one might write [math]\displaystyle{ -A }[/math] or [math]\displaystyle{ \overline{A} }[/math] instead, however the unary minus sign has a different meaning in programming.
A
|
not A
|
---|---|
false
|
true
|
true
|
false
|
not
has the highest precedence among logical operators.
bitwise operation
The bitwise not
flips every bit in an ordinal type.
not 1100'1010 ――――――――――――― 0011'0101
It effectively calculates the one's complement.
On virtually all platforms it is implemented by the not
instruction.
On NAND-gate-based architectures the not
instruction can be calculated by the expression [math]\displaystyle{ A \barwedge (111…111)_2 }[/math].
Note, that only not %0
will definitely result in a value interpretable as true
.
However, not every not x
will result in a value interpretable as false
, since only 0
is considered as false
and every other value as true
.