Label

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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”).