Example: passing parameters and return values using register
public class Prog {
/* ----------------------------------------------
sumSquares(a,b): returns (a*a + b*b)
---------------------------------------------- */
public static int sumSquares( int a, int b )
{
return (a*a + b*b);
}
public static void main( )
{
int x, y, z;
x = 4; y = 7;
z = sumSquares(x, y);
}
}
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How we will pass the parameters and return values
How do we write the main( ) function
main: sumSquares:
// Pass x in r0 // Compute x*x+y*y
// where x = r0 and y = r1
// Pass y in r1
// Return result in r0
bl sumSquares mov pc, lr
// Store return value
// in z
Stop:
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How do we write the main( ) function
main: sumSquares:
movw r0, #:lower16:x // Compute x*x+y*y
movt r0, #:upper16:x // where x = r0 and y = r1
ldr r0, [r0]
// Pass y in r1
// Return result in r0
bl sumSquares mov pc, lr
// Store return value
// in z
Stop:
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How do we write the main( ) function
main: sumSquares:
movw r0, #:lower16:x // Compute x*x+y*y
movt r0, #:upper16:x // where x = r0 and y = r1
ldr r0, [r0]
movw r1, #:lower16:y
movt r1, #:lower16:y
ldr r1, [r1] // Return result in r0
bl sumSquares mov pc, lr
// Store return value
// in z
Stop:
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How do we write the main( ) function
main: sumSquares:
movw r0, #:lower16:x // Compute x*x+y*y
movt r0, #:upper16:x // where x = r0 and y = r1
ldr r0, [r0]
movw r1, #:lower16:y
movt r1, #:lower16:y
ldr r1, [r1] // Return result in r0
bl sumSquares mov pc, lr
movw r1, #:lower16:z
movt r1, #:upper16:z
str r0, [r1]
Stop:
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How do we write the sumSquares( )
function
main: sumSquares:
movw r0, #:lower16:x // Compute x*x+y*y
movt r0, #:upper16:x // where x = r0 and y = r1
ldr r0, [r0]
movw r1, #:lower16:y
movt r1, #:lower16:y
ldr r1, [r1] // Return result in r0
bl sumSquares mov pc, lr
movw r1, #:lower16:z
movt r1, #:upper16:z
str r0, [r1]
Stop:
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How do we write the sumSquares( )
function
main: sumSquares:
movw r0, #:lower16:x // Compute x*x+y*y
movt r0, #:upper16:x // where x = r0 and y = r1
ldr r0, [r0] mul r2, r0, r0 // r2 = x*x
mul r3, r1, r1 // r3 = y*y
movw r1, #:lower16:y add r2, r2, r3 // r2 = x*x+y*y
movt r1, #:lower16:y
ldr r1, [r1] // Return result in r0
bl sumSquares mov pc, lr
movw r1, #:lower16:z
movt r1, #:upper16:z
str r0, [r1]
Stop:
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How do we write the sumSquares( )
function
main: sumSquares:
movw r0, #:lower16:x // Compute x*x+y*y
movt r0, #:upper16:x // where x = r0 and y = r1
ldr r0, [r0] mul r2, r0, r0 // r2 = x*x
mul r3, r1, r1 // r3 = y*y
movw r1, #:lower16:y add r2, r2, r3 // r2 = x*x+y*y
movt r1, #:lower16:y
ldr r1, [r1] mov r0, r2
bl sumSquares mov pc, lr
movw r1, #:lower16:z
movt r1, #:upper16:z
str r0, [r1]
Stop:
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DEMO: /home/cs255001/demo/asm/8-sub/reg-param1.s