C Program: Document every line: There are two seperate codes, in problem number
ID: 3600568 • Letter: C
Question
C Program: Document every line: There are two seperate codes, in problem number 2 explain what is going on with C code
1. Think of a c function int ReturnGreatest int *n1, int *n2, int *n3) which takes 3 address pointer and return the greatest number of all the three. Write a C code and then use the compiler to generate its corresponding assembly code for this function (assuming for a 32-bit machine). (15) Make sure your code has appropriate comments, so that it would be understandable 2. Have a look at the assembly code and explain what is being done here. Instead of explaining verbosely, you can write a c code to explain that (hints: this function is returning some value). Assignment method. pushl %ebp movl %esp,%ebp pushl %ebx movl 12(%ebp),%ecx movl 8(%ebp), %edx movl 4(%ebp),%esi movl (%ecx),%eax xorl %eax, %eax and/ %esi, %eax movl-41%ebp),%ebx movl %ebp,%esp popl %ebp reExplanation / Answer
C Code to accomplish the Greatest of 3 numbers:
#include <stdio.h>
int greatest3Numbers(int *, int *, int *);
int main()
{
int n1,n2,n3;//3 variables to hold 3 numbers.
int greatest; // to store the greatest of 3 numbers.
printf(" Enter Number 1: ");
scanf(" %d", &n1);
printf(" Enter Number 2: ");
scanf(" %d", &n2);
printf(" Enter Number 3: ");
scanf(" %d", &n3);
//Above code - logic to read each number
greatest = greatest3Numbers(&n1, &n2, &n3); //pass the address of each number
if(n1 == n2 && n1 == n3)
printf(" All the numbers are Equal"); // check if all numbers are equal
else
printf(" Greatest(%d, %d, %d) = %d", n1, n2, n3, greatest); // print the greatest.
printf(" ");
return 0;
}
int greatest3Numbers(int *a, int *b, int *c) {
int result;
if((*a >= *b) && (*a >= *c))
result = *a;
else if (*b >= *c)
result = *b;
else
result = *c;
return result;
}
Assembly Code:
.LC0:
.string " Enter Number 1: "
.LC1:
.string " %d"
.LC2:
.string " Enter Number 2: "
.LC3:
.string " Enter Number 3: "
.LC4:
.string " All the numbers are Equal"
.LC5:
.string " Greatest(%d, %d, %d) = %d"
.LC6:
.string " "
main:
push rbp
mov rbp, rsp
sub rsp, 16
mov edi, OFFSET FLAT:.LC0
mov eax, 0
call printf
lea rax, [rbp-8]
mov rsi, rax
mov edi, OFFSET FLAT:.LC1
mov eax, 0
call scanf
mov edi, OFFSET FLAT:.LC2
mov eax, 0
call printf
lea rax, [rbp-12]
mov rsi, rax
mov edi, OFFSET FLAT:.LC1
mov eax, 0
call scanf
mov edi, OFFSET FLAT:.LC3
mov eax, 0
call printf
lea rax, [rbp-16]
mov rsi, rax
mov edi, OFFSET FLAT:.LC1
mov eax, 0
call scanf
lea rdx, [rbp-16]
lea rcx, [rbp-12]
lea rax, [rbp-8]
mov rsi, rcx
mov rdi, rax
call greatest3Numbers(int*, int*, int*)
mov DWORD PTR [rbp-4], eax
mov edx, DWORD PTR [rbp-8]
mov eax, DWORD PTR [rbp-12]
cmp edx, eax
jne .L2
mov edx, DWORD PTR [rbp-8]
mov eax, DWORD PTR [rbp-16]
cmp edx, eax
jne .L2
mov edi, OFFSET FLAT:.LC4
mov eax, 0
call printf
jmp .L3
.L2:
mov ecx, DWORD PTR [rbp-16]
mov edx, DWORD PTR [rbp-12]
mov eax, DWORD PTR [rbp-8]
mov esi, DWORD PTR [rbp-4]
mov r8d, esi
mov esi, eax
mov edi, OFFSET FLAT:.LC5
mov eax, 0
call printf
.L3:
mov edi, OFFSET FLAT:.LC6
call puts
mov eax, 0
leave
ret
greatest3Numbers(int*, int*, int*):
push rbp
mov rbp, rsp
mov QWORD PTR [rbp-24], rdi
mov QWORD PTR [rbp-32], rsi
mov QWORD PTR [rbp-40], rdx
mov rax, QWORD PTR [rbp-24]
mov edx, DWORD PTR [rax]
mov rax, QWORD PTR [rbp-32]
mov eax, DWORD PTR [rax]
cmp edx, eax
jl .L6
mov rax, QWORD PTR [rbp-24]
mov edx, DWORD PTR [rax]
mov rax, QWORD PTR [rbp-40]
mov eax, DWORD PTR [rax]
cmp edx, eax
jl .L6
mov rax, QWORD PTR [rbp-24]
mov eax, DWORD PTR [rax]
mov DWORD PTR [rbp-4], eax
jmp .L7
.L6:
mov rax, QWORD PTR [rbp-32]
mov edx, DWORD PTR [rax]
mov rax, QWORD PTR [rbp-40]
mov eax, DWORD PTR [rax]
cmp edx, eax
jl .L8
mov rax, QWORD PTR [rbp-32]
mov eax, DWORD PTR [rax]
mov DWORD PTR [rbp-4], eax
jmp .L7
.L8:
mov rax, QWORD PTR [rbp-40]
mov eax, DWORD PTR [rax]
mov DWORD PTR [rbp-4], eax
.L7:
mov eax, DWORD PTR [rbp-4]
pop rbp
ret
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