Difference between revisions of "Not"
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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>. | 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>. | 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>. | ||
| + | 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 == | == see also == | ||
* {{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 16:10, 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
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not A
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false
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true
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true
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false
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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 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.
