Asm/fi: what changed

Revision 0 to 1. Removed lines have a minus sign; added lines have a plus sign.

Title: Asm/fi

New		Line
1	+	[[Reserved word\|Varattu sana]] `asm` aloittaa [[Block\|lohkon]] sisäiselle [[Assembly language/fi\|assembly]] koodille.
2	+
3	+	``` pascal
4	+	program asmDemo(input, output, stderr);
5	+
6	+	// The $asmMode directive informs the compiler
7	+	// which syntax is used in asm-blocks.
8	+	// Alternatives are 'att' (AT&T syntax) and 'direct'.
9	+	{$asmMode intel}
10	+
11	+	var
12	+	n, m: longint;
13	+	begin
14	+	n := 42;
15	+	m := -7;
16	+	writeLn('n = ', n, '; m = ', m);
17	+
18	+	// instead of declaring another temporary variable
19	+	// and writing "tmp := n; n := m; m := tmp;":
20	+	asm
21	+	mov eax, n // eax := n
22	+	// xchg can only operate at most on one memory address
23	+	xchg eax, m // swaps values in eax and at m
24	+	mov n, eax // n := eax (holding the former m value)
25	+	// an array of strings after the asm-block closing 'end'
26	+	// tells the compiler which registers have changed
27	+	// (you don't wanna mess with the compiler's notion
28	+	// which registers mean what)
29	+	end ['eax'];
30	+
31	+	writeLn('n = ', n, '; m = ', m);
32	+	end.
33	+	```
34	+
35	+	Jotta saataisiin siirrettävyys eri alustojen välillä (eli koodi voitaisiin edelleen koota moniin ympäristöihin), samalla kun halutaan optimoida tiettyjä laitteita, niin asetetaan [[Conditional compilation\|ehdollinen kääntäminen]]:
36	+
37	+	``` pascal
38	+	program sign(input, output, stderr);
39	+
40	+	type
41	+	signumCodomain = -1..1;
42	+
43	+	{ returns the sign of an integer }
44	+	function signum(const x: longint): signumCodomain;
45	+	{$ifdef CPUx86_64} // ============= optimized implementation
46	+	assembler;
47	+	{$asmMode intel}
48	+	asm
49	+	// load constants: cmov cannot handle immediates
50	+	// xor-instruction modifies flags => put it prior test
51	+	xor r8, r8 // r8 := 0
52	+
53	+	// comparison pulled up front for pipelining
54	+	test x, x // x = 0 ?
55	+
56	+	// load constants, since cmov cannot handle immediates
57	+	mov r9, -1 // r9 := -1
58	+
59	+	// determine result
60	+	mov eax, 1 // result := 1
61	+	cmovl eax, r9 // if x < 0 then result := -1
62	+	cmove eax, r8 // if x = 0 then result := 0
63	+	end;
64	+	{$else} // ========================== default implementation
65	+	begin
66	+	// This is what virtually math.sign does.
67	+	// The compiled code requires _two_ cmp instructions, though.
68	+	if x > 0 then
69	+	begin
70	+	signum := 1;
71	+	end
72	+	else if x < 0 then
73	+	begin
74	+	signum := -1;
75	+	end
76	+	else
77	+	begin
78	+	signum := 0;
79	+	end;
80	+	end;
81	+	{$endif}
82	+
83	+	// M A I N =================================================
84	+	var
85	+	x: longint;
86	+	begin
87	+	readLn(x);
88	+	writeLn(signum(x));
89	+	end.
90	+	```
91	+
92	+	Kuten nähdään niin voidaan toteuttaa kokonaisia rutiineja assembly kielellä lisäämällä `assembler` modifioija ja kirjoittamalla `asm` sen sijaan, että se aloitettaisiin [[Begin/fi\|begin]] toteutuslohkolla.
93	+
94	+	## Katso myös
95	+
96	+	Yleistä
97	+
98	+	- [[The inline assembler parser]]
99	+	- [[Lazarus inline assembler]]
100	+	- [[Label\|label § “assembler”]]
101	+
102	+	Merkitykselliset kääntäjänohjeet
103	+
104	+	- [[sAsmmode\|{$asmMode}]]
105	+	- [[sGoto\|{$goto}]]
106	+	- [[sStackFrames\|{$stackframes}]]
107	+
108	+	Erityistehtävät
109	+
110	+	- [[Hardware Access\|hardware access]]
111	+	- [[AVR Programming\|AVR programming]]
112	+
113	+	---
114	+	From the Free Pascal wiki, page "Asm/fi", as it stood on 2022-08-06 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).

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