Difference between revisions of "Not"

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{{not}}
 
{{not}}
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<br>
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The unary operator <syntaxhighlight lang="pascal" enclose="none">not</syntaxhighlight> negates a Boolean value.
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<br>
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[[FPC]] also knows the bitwise <syntaxhighlight lang="pascal" enclose="none">not</syntaxhighlight> when supplied with an ordinal type.
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__TOC__
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<syntaxhighlight lang="pascal" enclose="none">not</syntaxhighlight> is a reserved word.
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== 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>.
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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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'''Not''' produces a value of [[True|true]] if original value is [[False|false]].
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{| class="wikitable" style="text-align:center; margin:auto;"
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! <syntaxhighlight lang="pascal" enclose="none">A</syntaxhighlight>
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=== Truth table ===
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! <syntaxhighlight lang="pascal" enclose="none">not A</syntaxhighlight>
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{| class="wikitable"
 
 
|-
 
|-
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! A !! Not A
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| <syntaxhighlight lang="pascal" enclose="none">false</syntaxhighlight>
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| style="background: #eeeeee" | <syntaxhighlight lang="pascal" enclose="none">true</syntaxhighlight>
 
|-
 
|-
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| &nbsp; false &nbsp;
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| <syntaxhighlight lang="pascal" enclose="none">true</syntaxhighlight>
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|style="background: #eeeeee" | &nbsp; true
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| style="background: #eeeeee" | <syntaxhighlight lang="pascal" enclose="none">false</syntaxhighlight>
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|-
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|+ truth table for logical negation
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| &nbsp; true &nbsp;
 
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|style="background: #eeeeee" | &nbsp; false &nbsp;
 
 
|}
 
|}
  
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<syntaxhighlight lang="pascal" enclose="none">not</syntaxhighlight> has the highest precedence among logical operators.
  
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== Bitwise operation ==
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== bitwise operation ==
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The bitwise <syntaxhighlight lang="pascal" enclose="none">not</syntaxhighlight> flips every bit in an ordinal type.
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Bitwise '''not''' sets the bit to 1 if corresponding bit is 0, and to 0 if bit is 1.
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  not 1100'1010
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  ―――――――――――――
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=== Ones' complement ===
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    0011'0101
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It effectively calculates the one's complement.
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<syntaxhighlight>
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On virtually all platforms it is implemented by the <syntaxhighlight lang="asm" enclose="none">not</syntaxhighlight> instruction.
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  function OnesComplement ( const aValue : byte ): byte;
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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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  begin
 
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  result := Not AValue;
 
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end;
 
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</syntaxhighlight>
 
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If you call OnesComplement([[Percent sign|%]]10000000) then you get %01111111 (%10000000 = 128 and %01111111 = 127). If you call OnesComplement(%00000111) then you get 248 (248 = %11111000).
 
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<syntaxhighlight>
 
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function OnesComplement2 ( const aValue : shortint ): shortint;
 
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begin
 
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  result := Not AValue;
 
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end;
 
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</syntaxhighlight>
 
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If you call OnesComplement2(%00000010) then you get %11111101 (%00000010 = 2 and %11111101 = -3 when [[Type|type]] is shortint). If you call OnesComplement2(7) then you get -8 (-8 = %11111000  when type is shortint and 7 = %00000111 ).
 
  
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== See also ==
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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>.
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* [[And]]
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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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* [[Not]]
 
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* [[Shl]]
 
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* [[Const]]
 
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* [[Function]]
 
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* [[Byte]]
 
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* [[Shortint]]
 
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* [[Shl#Clear_a_bit| Clear_a_bit]] (bitwise example)
 
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* [[Bit manipulation]]
 
  
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[[Category:Pascal]]
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== 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>}}

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
truth table for logical negation

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.

see also

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