Page 130 - ARM 64 Bit Assembly Language

116 Chapter 5

Listing 5.3 Selection in C.
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1 . .
2 static int a,b,x;
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3 . .
4 if(a<b)
5 x=1;
6 else
7 x=0;
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8 . .

Listing 5.4 Selection in AArch64 assembly using branch instructions.
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1 . .
2 adr x0, a // load pointer to a
3 adr x1, b // load pointer to b
4 ldr x0, [x0] // load a
5 ldr x1, [x1] // load b
6 if:
7 cmp x0, x1 // compare them
8 bge else // if a >= b then skip forward
9 mov x0, #1 // THEN section - load 1 into x0
10 b endif // skip the else section
11 else:
12 mov x0, #0 // ELSE section - load 0 into x0
13 endif:
14 adr x1, x // load pointer to x
15 str x0, [x1] // store x0 in x
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16 . .

Listing 5.5 Selection in AArch64 assembly using a conditional instruction.
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1 . .
2 adr x0, a // load pointer to a
3 adr x1, b // load pointer to b
4 ldr x0, [x0] // load a
5 ldr x1, [x1] // load b
6 cmp x0, x1 // compare them
7 cset x0, lt // Conditionally set x0 to 1 if a
8 adr x1, x // load pointer to x
9 str x0, [x1] // store x0 in x
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10 . .