Difference between revisions of "Or"
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{{Or}} | {{Or}} | ||
− | = Boolean | + | The [[Reserved word|reserved word]] <syntaxhighlight lang="pascal" enclose="none">or</syntaxhighlight> is a binary [[Operator|operator]]. |
+ | Originally it stood for the logical disjunction of two [[Boolean|boolean values]] only, but with the advent of [[Operator overloading|operator overloading]] [[FPC]] allows everything else, too. | ||
+ | FPC also defines the <syntaxhighlight lang="pascal" enclose="none">or</syntaxhighlight> operator taking two integer types acts on their internal binary representation. | ||
− | + | == boolean operation == | |
+ | The expression <syntaxhighlight lang="pascal" enclose="none">A or B</syntaxhighlight> represents the term <math>A \land B</math> as it is familiar from classical logic. | ||
+ | In electrical engineering writing <math>A + B</math> is common, too, but in programming of the [[Plus|plus-sign]] is different. | ||
+ | <syntaxhighlight lang="pascal" enclose="none">A</syntaxhighlight> and <syntaxhighlight lang="pascal" enclose="none">B</syntaxhighlight> are both boolean values. | ||
+ | The expression evaluates to either [[false and true|<syntaxhighlight lang="pascal" enclose="none">true</syntaxhighlight> or <syntaxhighlight lang="pascal" enclose="none">false</syntaxhighlight>]]. | ||
+ | It is only <syntaxhighlight lang="pascal" enclose="none">false</syntaxhighlight> if both operands are <syntaxhighlight lang="pascal" enclose="none">false</syntaxhighlight>: | ||
− | + | {| class="wikitable" style="text-align:center; margin:auto;" | |
− | + | ! <syntaxhighlight lang="pascal" enclose="none">A</syntaxhighlight> | |
− | {| class="wikitable" | + | ! <syntaxhighlight lang="pascal" enclose="none">B</syntaxhighlight> |
− | + | ! <syntaxhighlight lang="pascal" enclose="none">A or B</syntaxhighlight> | |
− | ! A ! | ||
|- | |- | ||
− | | | + | | <syntaxhighlight lang="pascal" enclose="none">false</syntaxhighlight> |
− | |style="background: #eeeeee" | | + | | <syntaxhighlight lang="pascal" enclose="none">false</syntaxhighlight> |
+ | | style="background: #eeeeee" | <syntaxhighlight lang="pascal" enclose="none">false</syntaxhighlight> | ||
|- | |- | ||
− | | | + | | <syntaxhighlight lang="pascal" enclose="none">false</syntaxhighlight> |
− | |style="background: #eeeeee" | | + | | <syntaxhighlight lang="pascal" enclose="none">true</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> |
+ | | 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">true</syntaxhighlight> |
+ | | style="background: #eeeeee" | <syntaxhighlight lang="pascal" enclose="none">true</syntaxhighlight> | ||
+ | |+ truth table for logical disjunction | ||
|} | |} | ||
− | = | + | == bitwise operation == |
+ | Since virtually all instruction sets have an <syntaxhighlight lang="asm" enclose="none">or</syntaxhighlight> instruction, it is no surprise some high-level languages, especially those which aim to be suitable for hardware programming, provide some comparable functionality by itself. | ||
+ | In FPC the <syntaxhighlight lang="pascal" enclose="none">or</syntaxhighlight> operator defined appropriately. | ||
+ | Such an expression, also known as bitwise or, requires two ordinal operands. | ||
+ | The operation virtually performs a logical or taking each corresponding bit from both operands. | ||
+ | 0101'1010 | ||
+ | or 0000'1011 | ||
+ | ―――――――――――― | ||
+ | 0101'1011 | ||
− | + | === setting a bit === | |
+ | A common task is to set a specific bit. | ||
+ | To achieve this utilizing the <syntaxhighlight lang="pascal" enclose="none">or</syntaxhighlight> operator elicits a smart implementation: | ||
+ | <syntaxhighlight lang="pascal"> | ||
+ | type | ||
+ | integerBitIndex = 0..bitSizeOf(integer)-1; | ||
− | + | {$push} | |
− | + | {$rangeChecks on} // instead of an exception will generate an RTE | |
− | function | + | function maskOn(const x: integer; const i: integerBitIndex): integer; |
begin | begin | ||
− | + | maskOn := x or (%1 shl i); | |
end; | end; | ||
+ | {$pop} | ||
</syntaxhighlight> | </syntaxhighlight> | ||
− | + | For example calling <syntaxhighlight lang="delphi" enclose="none">maskOn(%1000, 1)</syntaxhighlight> will result in <syntaxhighlight lang="delphi" enclose="none">%1010</syntaxhighlight> (<syntaxhighlight lang="delphi" enclose="none">%1000</syntaxhighlight> equals decimal eight, and <syntaxhighlight lang="delphi" enclose="none">%1010</syntaxhighlight> is ten). | |
+ | |||
+ | === comparative remarks === | ||
+ | Note: | ||
+ | The concept of [[Set|sets]] is an integral part of Pascal. | ||
+ | Whilst in other programming languages considering operations on the bit level is not unusual, Pascal provides you with a notion that relieves you from the burden of thinking about bits. | ||
+ | Take it under advisement whether your programming task can be modeled with sets even better. | ||
+ | |||
+ | == see also == | ||
+ | * [https://www.freepascal.org/docs-html/ref/refsu47.html § “boolean operators” in the “Free Pascal Reference Guide”] regarding the logical disjunction | ||
+ | * [https://www.freepascal.org/docs-html/ref/refsu46.html § “logical operators” in the “Free Pascal Reference Guide”] regarding the bitwise <syntaxhighlight lang="pascal" enclose="none">or</syntaxhighlight> | ||
+ | * [[And|<syntaxhighlight lang="pascal" enclose="none">and</syntaxhighlight>]] | ||
+ | * {{Doc|package=RTL|unit=system|identifier=.op-logicalor-variant-ariant-ariant|text=<syntaxhighlight lang="pascal" enclose="none">system.logicalor</syntaxhighlight>}} | ||
− | + | [[Category:Pascal]] | |
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Revision as of 14:39, 26 October 2018
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The reserved word or
is a binary operator.
Originally it stood for the logical disjunction of two boolean values only, but with the advent of operator overloading FPC allows everything else, too.
FPC also defines the or
operator taking two integer types acts on their internal binary representation.
boolean operation
The expression A or B
represents the term [math]\displaystyle{ A \land B }[/math] as it is familiar from classical logic.
In electrical engineering writing [math]\displaystyle{ A + B }[/math] is common, too, but in programming of the plus-sign is different.
A
and B
are both boolean values.
The expression evaluates to either true
or false
.
It is only false
if both operands are false
:
A
|
B
|
A or B
|
---|---|---|
false
|
false
|
false
|
false
|
true
|
true
|
true
|
false
|
true
|
true
|
true
|
true
|
bitwise operation
Since virtually all instruction sets have an or
instruction, it is no surprise some high-level languages, especially those which aim to be suitable for hardware programming, provide some comparable functionality by itself.
In FPC the or
operator defined appropriately.
Such an expression, also known as bitwise or, requires two ordinal operands.
The operation virtually performs a logical or taking each corresponding bit from both operands.
0101'1010 or 0000'1011 ―――――――――――― 0101'1011
setting a bit
A common task is to set a specific bit.
To achieve this utilizing the or
operator elicits a smart implementation:
type
integerBitIndex = 0..bitSizeOf(integer)-1;
{$push}
{$rangeChecks on} // instead of an exception will generate an RTE
function maskOn(const x: integer; const i: integerBitIndex): integer;
begin
maskOn := x or (%1 shl i);
end;
{$pop}
For example calling maskOn(%1000, 1)
will result in %1010
(%1000
equals decimal eight, and %1010
is ten).
comparative remarks
Note: The concept of sets is an integral part of Pascal. Whilst in other programming languages considering operations on the bit level is not unusual, Pascal provides you with a notion that relieves you from the burden of thinking about bits. Take it under advisement whether your programming task can be modeled with sets even better.
see also
- § “boolean operators” in the “Free Pascal Reference Guide” regarding the logical disjunction
- § “logical operators” in the “Free Pascal Reference Guide” regarding the bitwise
or
and
system.logicalor