JE, JNE and JMP

Part of the Arithmetic and Control Flow section of Coddy's Assembly journey. Lesson 7 of 28.

A label names a position in the instruction stream. je jumps when the zero flag is set; jne jumps when it is clear. jmp always jumps. Branches are just changes in which instruction runs next; mov does not change flags.

mov rax, 0
mov rbx, 5
cmp rbx, 5
jne .done
mov rax, 1
.done:

The values are equal, so jne is not taken and rax becomes 1.

Compare immediately before the conditional jump so it reads the intended flags.

Use these instruction excerpts inside the supplied solve routine; the challenge provides the input and output code.

Challenge

Easy

Return 1 when r8 equals r9, and 0 otherwise. Inputs are between -100 and 100. Use a comparison and a conditional jump.

Edit solution.asm between solve: and the supplied ret. The locked main.asm reads the test numbers into r8, r9, r10, and r11 in order, and also stores them as four consecutive 8-byte integers at values. Unused inputs are zero. Leave your answer in rax; the harness prints it as one signed decimal integer followed by a newline. Keep the supplied wrapper and do not print anything yourself.

Try it yourself

bits 64
section .bss
    input_buffer resb 256
    output_buffer resb 32
    values resq 4
section .text
    global _start
    global values
    extern solve
_start:
    xor eax, eax
    xor edi, edi
    mov rsi, input_buffer
    mov edx, 255
    syscall
    test rax, rax
    jle .loaded
    mov rsi, input_buffer
    lea rdi, [input_buffer + rax]
    xor ecx, ecx
.scan:
    cmp rsi, rdi
    jae .loaded
    cmp ecx, 4
    jae .loaded
    movzx eax, byte [rsi]
    cmp al, 32
    jbe .space
    mov r10, 1
    cmp al, '-'
    jne .number
    mov r10, -1
    inc rsi
.number:
    xor rax, rax
.digit:
    cmp rsi, rdi
    jae .store
    movzx edx, byte [rsi]
    cmp dl, '0'
    jb .store
    cmp dl, '9'
    ja .store
    imul rax, rax, 10
    sub edx, '0'
    add rax, rdx
    inc rsi
    jmp .digit
.store:
    imul rax, r10
    mov [values + rcx * 8], rax
    inc ecx
.space:
    inc rsi
    jmp .scan
.loaded:
    mov r8, [values]
    mov r9, [values + 8]
    mov r10, [values + 16]
    mov r11, [values + 24]
    xor eax, eax
    call solve
    lea rsi, [output_buffer + 31]
    mov byte [rsi], 10
    mov ecx, 1
    xor r8d, r8d
    test rax, rax
    jns .positive
    mov r8d, 1
    neg rax
.positive:
    mov ebx, 10
.convert:
    xor edx, edx
    div rbx
    add dl, '0'
    dec rsi
    mov [rsi], dl
    inc ecx
    test rax, rax
    jnz .convert
    test r8d, r8d
    jz .write
    dec rsi
    mov byte [rsi], '-'
    inc ecx
.write:
    mov edx, ecx
    mov eax, 1
    mov edi, 1
    syscall
    mov eax, 60
    xor edi, edi
    syscall