; x86_64 linux nasm

section .bss
number resb 4

section .data
fizz: db "Fizz"
buzz: db "Buzz"
newLine: db 10

section .text
global _start

_start:

  mov rax, 1      ; initialize counter

  loop:
    push rax
    call fizzBuzz
    pop rax
    inc rax
    cmp rax, 100
    jle loop

  mov rax, 60
  mov rdi, 0
  syscall

fizzBuzz:
  mov r10, rax
  mov r15, 0       ; boolean fizz or buzz
  checkFizz:
    xor rdx, rdx   ; clear rdx for division
    mov rbx, 3
    div rbx
    cmp rdx, 0     ; modulo result here
    jne checkBuzz
    mov r15, 1
    mov rsi, fizz
    mov rdx, 4
    mov rax, 1
    mov rdi, 1
    syscall
  checkBuzz:
    mov rax, r10
    xor rdx, rdx
    mov rbx, 5
    div rbx
    cmp rdx, 0
    jne finishLine
    mov r15, 1
    mov rsi, buzz
    mov rdx, 4
    mov rax, 1
    mov rdi, 1
    syscall
  finishLine:      ; print number if no fizz or buzz
    cmp r15, 1
    je nextLine
    mov rax, r10
    call printNum
    ret
    nextLine:
      mov rsi, newLine
      mov rdx, 1
      mov rax, 1
      mov rdi, 1
      syscall
      ret

printNum:          ; write proper digits into number buffer
  cmp rax, 100
  jl lessThanHundred
  mov byte [number], 49
  mov byte [number + 1], 48
  mov byte [number + 2], 48
  mov rdx, 3
  jmp print

  lessThanHundred: ; get digits to write through division
    xor rdx, rdx
    mov rbx, 10
    div rbx
    add rdx, 48
    cmp rax, 0
    je lessThanTen
    add rax, 48
    mov byte [number], al
    mov byte [number + 1], dl
    mov rdx, 2
    jmp print

  lessThanTen:
    mov byte [number], dl
    mov rdx, 1
  print:
    mov byte [number + rdx], 10   ; add newline
    inc rdx
    mov rax, 1
    mov rdi, 1
    mov rsi, number
    syscall
  ret