Or: what changed

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Title: Or

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1	+	The [[Reserved word\|reserved word]] `or` 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 `or` operator accepting two ordinal types while performing calculations on their internal binary representation.
2	+
3	+	## boolean operation
4	+
5	+	The expression `A or B` represents the term $`A \lor B`$ as it is familiar from classical logic. In electrical engineering writing $`A + B`$ is common, too, but in programming the meaning of the plus sign differs. `A` and `B` are both boolean values. The expression evaluates to either [[false and true\|true or false]]. It is only `false` if both operands are `false`:
6	+
7	+	\| `A` \| `B` \| `A or B` \|
8	+	\|---------\|---------\|----------\|
9	+	\| `false` \| `false` \| `false` \|
10	+	\| `false` \| `true` \| `true` \|
11	+	\| `true` \| `false` \| `true` \|
12	+	\| `true` \| `true` \| `true` \|
13	+
14	+	## bitwise operation
15	+
16	+	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 is 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.
17	+
18	+	` 0101'1010`\
19	+	`or 0000'1011`\
20	+	`――――――――――――`\
21	+	` 0101'1011`
22	+
23	+	For a typical usage example of `or` confer [[&\|program messageNo]]’s passing remark.
24	+
25	+	### setting a bit
26	+
27	+	A common task is to set a specific bit. To achieve this utilizing the `or` operator elicits a smart implementation:
28	+
29	+	``` pascal
30	+	type
31	+	integerBitIndex = 0..bitSizeOf(integer)-1;
32	+
33	+	{$push}
34	+	{$rangeChecks on} // instead of raising an exception, generate an RTE
35	+	function maskOn(const x: integer; const i: integerBitIndex): integer;
36	+	begin
37	+	maskOn := x or (%1 shl i);
38	+	end;
39	+	{$pop}
40	+	```
41	+
42	+	For example calling `maskOn(%1000, 1)` will result in `%1010` (`%1000` equals decimal eight, and `%1010` is ten).
43	+
44	+	### comparative remarks
45	+
46	+	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 powerful 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.
47	+
48	+	When using sets a [[Plus\|plus sign +]] virtually does the same as the bitwise `or` does (depends on the compiler’s implementation of the data type `set`). This notation is, as already mentioned above, familiar from electrical engineering. However, when handling sets the bitwise `or` is called a union (of sets).
49	+
50	+	## see also
51	+
52	+	- [§ “boolean operators” in the “Free Pascal Reference Guide”](https://www.freepascal.org/docs-html/ref/refsu46.html) regarding the logical disjunction
53	+	- [§ “logical operators” in the “Free Pascal Reference Guide”](https://www.freepascal.org/docs-html/ref/refsu45.html) regarding the bitwise `or`
54	+	- [[And\|and]]
55	+	- [[Xor\|xor]]
56	+	- [`system.logicalor`](https://www.freepascal.org/docs-html/rtl/system/.op-logicalor-variant-ariant-ariant.html)
57	+
58	+	---
59	+	From the Free Pascal wiki, page "Or", as it stood on 2022-02-21 after a change by Kai Burghardt, out of the wiki's dump of 2024-05-26. Copyright stays with the author who wrote it, according to the old wiki's [[Licensing]] page. If you have concerns about this material, [message the admin](/wiki-contact).
60	+	Category: Code

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