Question

Write the LEGv8 assembly program for following c program. Assume array1, array2 and array3 are
stored in memory with base addresses at 1000, 2000 and 3000 respectively.

int absoluteDifference(int x, int y) {
int r;
if (x > y)
r = x - y;
else
r = y - x;
return r;
}
int main() {
for (int i=0; i < 10; i++) {
int a = array1[i];
int b = array2[i];
int c = absoluteDifference(a, b);
array3[i] = c;
}
}

Answer 1

The has modified to get the result

#include <iostream>
using namespace std;
 int absoluteDifference(int x, int y) {
int r;
if (x > y)
r = x - y;
else
r = y - x;
return r;
}
int main() {
    int array1=1000,array2=2000,array3=3000;{

 array3 = absoluteDifference(array1, array2);
cout<<"The absolute difference is: "<< array3;
}
}

The conversion to the assembly language

absoluteDifference(int, int):
        push    rbp
        mov     rbp, rsp
        mov     DWORD PTR [rbp-20], edi
        mov     DWORD PTR [rbp-24], esi
        mov     eax, DWORD PTR [rbp-20]
        cmp     eax, DWORD PTR [rbp-24]
        jle     .L2
        mov     eax, DWORD PTR [rbp-20]
        sub     eax, DWORD PTR [rbp-24]
        mov     DWORD PTR [rbp-4], eax
        jmp     .L3
.L2:
        mov     eax, DWORD PTR [rbp-24]
        sub     eax, DWORD PTR [rbp-20]
        mov     DWORD PTR [rbp-4], eax
.L3:
        mov     eax, DWORD PTR [rbp-4]
        pop     rbp
        ret
.LC0:
        .string "The absolute difference is: "
main:
        push    rbp
        mov     rbp, rsp
        sub     rsp, 16
        mov     DWORD PTR [rbp-4], 1000
        mov     DWORD PTR [rbp-8], 2000
        mov     DWORD PTR [rbp-12], 3000
        mov     edx, DWORD PTR [rbp-8]
        mov     eax, DWORD PTR [rbp-4]
        mov     esi, edx
        mov     edi, eax
        call    absoluteDifference(int, int)
        mov     DWORD PTR [rbp-12], eax
        mov     esi, OFFSET FLAT:.LC0
        mov     edi, OFFSET FLAT:_ZSt4cout
        call    std::basic_ostream<char, std::char_traits<char> >& std::operator<< <std::char_traits<char> >(std::basic_ostream<char, std::char_traits<char> >&, char const*)
        mov     rdx, rax
        mov     eax, DWORD PTR [rbp-12]
        mov     esi, eax
        mov     rdi, rdx
        call    std::basic_ostream<char, std::char_traits<char> >::operator<<(int)
        mov     eax, 0
        leave
        ret
__static_initialization_and_destruction_0(int, int):
        push    rbp
        mov     rbp, rsp
        sub     rsp, 16
        mov     DWORD PTR [rbp-4], edi
        mov     DWORD PTR [rbp-8], esi
        cmp     DWORD PTR [rbp-4], 1
        jne     .L9
        cmp     DWORD PTR [rbp-8], 65535
        jne     .L9
        mov     edi, OFFSET FLAT:_ZStL8__ioinit
        call    std::ios_base::Init::Init() [complete object constructor]
        mov     edx, OFFSET FLAT:__dso_handle
        mov     esi, OFFSET FLAT:_ZStL8__ioinit
        mov     edi, OFFSET FLAT:_ZNSt8ios_base4InitD1Ev
        call    __cxa_atexit
.L9:
        nop
        leave
        ret
_GLOBAL__sub_I_absoluteDifference(int, int):
        push    rbp
        mov     rbp, rsp
        mov     esi, 65535
        mov     edi, 1
        call    __static_initialization_and_destruction_0(int, int)
        pop     rbp
        ret

The ouput