Difference between revisions of "Label"
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{{label}} | {{label}} | ||
| − | The < | + | The <syntaxhighlight lang="pascal" enclose="none">label</syntaxhighlight> keyword is used for declaration of labels (markers for unconditional jumps using [[Goto|<syntaxhighlight lang="pascal" enclose="none">goto</syntaxhighlight>]] keyword) used further in the [[Unit|<syntaxhighlight lang="pascal" enclose="none">unit</syntaxhighlight>]]/[[Program|<syntaxhighlight lang="pascal" enclose="none">program</syntaxhighlight>]]. |
| − | A < | + | A <syntaxhighlight lang="pascal" enclose="none">label</syntaxhighlight> section is also required for jump targets in [[Asm|<syntaxhighlight lang="pascal" enclose="none">asm</syntaxhighlight>-blocks]]. |
| − | <syntaxhighlight>program sumExample(input, output, stderr); | + | <syntaxhighlight lang="pascal" start="0" line highlight="8-12,18">program sumExample(input, output, stderr); |
{ iteratively calculates the sum over first n integers } | { iteratively calculates the sum over first n integers } | ||
| Line 53: | Line 53: | ||
writeLn(iterativeSumFirstNIntegers(n)); | writeLn(iterativeSumFirstNIntegers(n)); | ||
end.</syntaxhighlight> | end.</syntaxhighlight> | ||
| − | Of course in a production program, you would use an algorithm applying the formula < | + | Of course in a production program, you would use an algorithm applying the formula <syntaxhighlight lang="pascal" enclose="none">sum := (n * (n + 1)) div 2</syntaxhighlight> (“Gaussian sum formula”). |
| − | |||
[[category:Pascal]] | [[category:Pascal]] | ||
[[Category:Control Structures]] | [[Category:Control Structures]] | ||
Revision as of 17:35, 11 February 2018
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The label keyword is used for declaration of labels (markers for unconditional jumps using goto keyword) used further in the unit/program.
A label section is also required for jump targets in asm-blocks.
0program sumExample(input, output, stderr);
1
2{ iteratively calculates the sum over first n integers }
3function iterativeSumFirstNIntegers(const n: longword): qword;
4{$ifdef CPUX86_64} // ============= optimized implementation
5// assembler modifier appended to routine declaration
6assembler;
7// you have to familiarize the compiler with symbols
8// which are meant to be jump targets
9{$goto on}
10label
11 isfni_iterate;
12{$asmMode intel}
13asm
14 xor rax, rax // rax := 0
15 // ecx is used as counter by loop instruction
16 mov ecx, n // ecx := n
17isfni_iterate:
18 add rax, qword(ecx) // rax := rax + ecx
19 loop isfni_iterate // dec(ecx)
20 // if ecx <> 0 then goto isfni_iterate
21
22 // the @result macro represents the functions return value
23 mov @result, rax // result := rax
24// note, a list of modified registers (here ['rax', 'ecx'])
25// is ignored for pure assembler routines
26end;
27{$else} // ========================== default implementation
28var
29 i: longword;
30 x: qword;
31begin
32 x := 0; // mov rax, 0
33 for i := n downto 1 do // mov ecx, n
34 begin
35 x := x + i; // add rax, ecx
36 end; // loop isfni_iterate
37 iterativeSumFirstNIntegers := x; // mov @result, rax
38end;
39{$endif}
40
41// M A I N =================================================
42var
43 n: longword;
44begin
45 readLn(n);
46 writeLn(iterativeSumFirstNIntegers(n));
47end.
Of course in a production program, you would use an algorithm applying the formula sum := (n * (n + 1)) div 2 (“Gaussian sum formula”).
