Question

Take the following program and translate it into PEP/9 assembly language:

#include using namespace std; int fib(int n) { int temp; if (n <= 0) return 0; else if (n <= 2) return 1; else { temp = fib(n – 1); return temp + fib(n-2); } } int main() { int num; cout << "Which fibonacci number? "; cin >> num; cout << fib(num) << endl; return 0; }

You must use equates to access the stack and follow the call to the function as discussed in the book (pass the parameter, return address, return a value and so on). There are NO global variables in the resulting code (except a global message of "Range num? "). It must be able to do sum a range greater than 2.

Answer 1

Here is the code conversion of C++ into Assembly Language.

fib(int):
        push    rbp
        mov     rbp, rsp
        sub     rsp, 32
        mov     DWORD PTR [rbp-20], edi
        cmp     DWORD PTR [rbp-20], 0
        jg      .L2
        mov     eax, 0
        jmp     .L3
.L2:
        cmp     DWORD PTR [rbp-20], 2
        jg      .L4
        mov     eax, 1
        jmp     .L3
.L4:
        mov     eax, DWORD PTR [rbp-20]
        sub     eax, 1
        mov     edi, eax
        call    fib(int)
        mov     DWORD PTR [rbp-4], eax
        mov     eax, DWORD PTR [rbp-20]
        sub     eax, 2
        mov     edi, eax
        call    fib(int)
        mov     edx, DWORD PTR [rbp-4]
        add     eax, edx
.L3:
        leave
        ret
.LC0:
        .string "Which fibonacci number? "
main:
        push    rbp
        mov     rbp, rsp
        sub     rsp, 16
        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*)
        lea     rax, [rbp-4]
        mov     rsi, rax
        mov     edi, OFFSET FLAT:_ZSt3cin
        call    std::basic_istream<char, std::char_traits<char> >::operator>>(int&)
        mov     eax, DWORD PTR [rbp-4]
        mov     edi, eax
        call    fib(int)
        mov     esi, eax
        mov     edi, OFFSET FLAT:_ZSt4cout
        call    std::basic_ostream<char, std::char_traits<char> >::operator<<(int)
        mov     esi, OFFSET FLAT:_ZSt4endlIcSt11char_traitsIcEERSt13basic_ostreamIT_T0_ES6_
        mov     rdi, rax
        call    std::basic_ostream<char, std::char_traits<char> >::operator<<(std::basic_ostream<char, std::char_traits<char> >& (*)(std::basic_ostream<char, std::char_traits<char> >&))
        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_fib(int):
        push    rbp
        mov     rbp, rsp
        mov     esi, 65535
        mov     edi, 1
        call    __static_initialization_and_destruction_0(int, int)
        pop     rbp
        ret