I could use some help with this code:

4. Analyze the x86-64 assembly given below.

char_out: subq $8, %rsp movsbl %dil, %edi # Parameter 1 in %dil / %edi. call putchar # putchar is a C function that writes (prints) addq $8, %rsp # a single char to stdout (the screen). ret sub_mystery: subq $8, %rsp cmpq $9, %rdi # Parameter 1 in %rdi ja .L4 addl $48, %edi movsbl %dil, %edi call char_out jmp .L3 .L4: addl $55, %edi movsbl %dil, %edi call char_out .L3: addq $8, %rsp ret

mystery: pushq %r12 pushq %rbp # Saving registers, not relevant. pushq %rbx movq %rdi, %rax # Parameter 1 in %rdi, copy into Local 1,%rax. movl $1, %ebx # Local 2 in %ebx (or %rbx). jmp .L8 .L9: salq $4, %rbx shrq $4, %rax .L8: cmpq $15, %rax ja .L9 movl $0, %ebp # Local 3 in %ebp/rbp, it's not the base pointer! jmp .L10 .L11: movq %rdi, %rax movl $0, %edx divq %rbx # Division instruction, divides %rax / %rbx movq %rdx, %r12 # Remainder is stored in %rdx. movq %rax, %rdi # Quotient is stored in %rax. call sub_mystery addl $1, %ebp movq %r12, %rdi shrq $4, %rbx .L10: testq %rbx, %rbx jne .L11 movl %ebp, %eax popq %rbx # Restoring saved registers, also not relevant. popq %rbp popq %r12 ret

For the questions below, when you are asked to write C code suppose that any parameters are named P1, P2, etc., in the order the parameters would be listed in the C code. Suppose the local variables are called L1, L2, etc., in the order they occur in the x86-64 assembly, i.e. %eax (or %rax) is the first local variable.

Be advised: you may derive a perfectly acceptable answer and find that when you compile it you get slightly different assembly code. Minor differences should be expected, so don't tweak your C code trying to replicate the assembly code exactly.

Note: this code has been optimized and doesn't manipulate the stack (much). Some registers represent local variables, while others are parameters, recall which registers hold parameters.

a.[10 points] Write C code for the function that could have yielded the x86-64 assembly code given above for char_out(). This should be a one liner. Your final answer must not include any goto statements!

b.[10 points] Write C code for the function that could have yielded the x86-64 assembly code given above for sub_mystery(). Your final answer must not include any goto statements!

c.[20 points] Write C code for the function that could have yielded the x86-64 assembly code given above formystery(). Your final answer must not include any goto statements!

#include #include

// Q4A // // // void char_out(char P1) {

}

// Q4B // // // void sub_mystery(uint64_t P1) {

}

// Q4C // // // int mystery(uint64_t P1) { return 0; }