Difference between revisions of "Not"
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The unary operator <syntaxhighlight lang="pascal" enclose="none">not</syntaxhighlight> negates a Boolean value. | 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. | [[FPC]] also knows the bitwise <syntaxhighlight lang="pascal" enclose="none">not</syntaxhighlight> when supplied with an ordinal type. | ||
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<syntaxhighlight lang="pascal" enclose="none">not</syntaxhighlight> is a reserved word. | <syntaxhighlight lang="pascal" enclose="none">not</syntaxhighlight> is a reserved word. | ||
== Boolean operation == | == Boolean operation == | ||
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The operator <syntaxhighlight lang="pascal" enclose="none">not</syntaxhighlight> represent the logical negation <math>\neg A</math>. | 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. | 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. | ||
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| <syntaxhighlight lang="pascal" enclose="none">true</syntaxhighlight> | | <syntaxhighlight lang="pascal" enclose="none">true</syntaxhighlight> | ||
| style="background: #eeeeee" | <syntaxhighlight lang="pascal" enclose="none">false</syntaxhighlight> | | style="background: #eeeeee" | <syntaxhighlight lang="pascal" enclose="none">false</syntaxhighlight> | ||
| − | |+ | + | |+ Truth table for logical negation |
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<syntaxhighlight lang="pascal" enclose="none">not</syntaxhighlight> has the highest precedence among logical operators. | <syntaxhighlight lang="pascal" enclose="none">not</syntaxhighlight> has the highest precedence among logical operators. | ||
| − | == | + | == Bitwise operation == |
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The bitwise <syntaxhighlight lang="pascal" enclose="none">not</syntaxhighlight> flips every bit in an ordinal type. | The bitwise <syntaxhighlight lang="pascal" enclose="none">not</syntaxhighlight> flips every bit in an ordinal type. | ||
not 1100'1010 | not 1100'1010 | ||
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It effectively calculates the one's complement. | It effectively calculates the one's complement. | ||
On virtually all platforms it is implemented by the <syntaxhighlight lang="asm" enclose="none">not</syntaxhighlight> instruction. | 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 | + | On NAND-gate-based architectures the <syntaxhighlight lang="asm" enclose="none">not</syntaxhighlight> instruction can be calculated by the expression <math>A ⌅ A</math>. |
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>. | 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>. | ||
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For example, <syntaxhighlight lang="delphi" enclose="none">boolean(not %1)</syntaxhighlight> will evaluate as <syntaxhighlight lang="pascal" enclose="none">true</syntaxhighlight>, but only <syntaxhighlight lang="delphi" enclose="none">boolean(not high(nativeUInt))</syntaxhighlight> will evaluate to <syntaxhighlight lang="pascal" enclose="none">false</syntaxhighlight>. | For example, <syntaxhighlight lang="delphi" enclose="none">boolean(not %1)</syntaxhighlight> will evaluate as <syntaxhighlight lang="pascal" enclose="none">true</syntaxhighlight>, but only <syntaxhighlight lang="delphi" enclose="none">boolean(not high(nativeUInt))</syntaxhighlight> will evaluate to <syntaxhighlight lang="pascal" enclose="none">false</syntaxhighlight>. | ||
| − | == | + | == See also == |
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* {{Doc|package=RTL|unit=system|identifier=.op-logicalnot-variant-ariant|text=<syntaxhighlight lang="pascal" enclose="none">system.logicalNot</syntaxhighlight>}} | * {{Doc|package=RTL|unit=system|identifier=.op-logicalnot-variant-ariant|text=<syntaxhighlight lang="pascal" enclose="none">system.logicalNot</syntaxhighlight>}} | ||
Revision as of 10:30, 21 February 2020
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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 ⌅ A }[/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.
For example, boolean(not %1) will evaluate as true, but only boolean(not high(nativeUInt)) will evaluate to false.
