sol.asm

; constants
section .data
  lblZero:      db    'Zero';
  lblOne:       db    'One ';
  lblNumLength: db    0x4;
  lblErr:       db    'There was an error.', 10;
  lblErrLength:       equ $ - lblErr;
  lblInput:     db    'Type a single digit number: ', 10;
  lblInputLength:     equ $ - lblInput;
  tmp:          db    0;
  lblByeBye:    db    'Good bye!', 10 ;
  lblByeByeLength:    equ $ - lblByeBye;

; code
section .text
  global _start

; linker needs this, 'main'
_start:

loop:
  ; prompt user for a digit ; sys_write
  mov rax, 1 ;
  mov rdi, 1 ;
  mov rsi, lblInput ;
  mov rdx, lblInputLength ;
  syscall
  ; store user's input ; read
  mov rax, 0 ;
  mov rbx, 19 ;
  mov rcx, tmp ;
  mov rdx, 10 ;
  syscall
  ; series of IFs
  cmp   rcx, 0x0    ; is input 0? 00 exits the program
  je    isZero
  cmp   rcx, '1'    ; is input 1?
  je    isOne  
  jmp   exit               ; case default

; user typed 0
isZero:
  inc   rcx               ; flag for 0
  cmp   rcx, 2            ; checking if this is the 2nd zero
  je    exit              ; if so, we are outta here
  mov   rsi, lblZero ;
  mov   rcx, -1 ;
  jmp  print ;

; user typed 1
isOne:
  mov   rsi, lblOne ;
  mov   rcx, -1 ;
  jmp  print ;

; prints the string into the screen ; sys_write
print:
  mov   rax, 1 ;           
  mov   rdi, 1 ;         
  mov   rdx, lblNumLength ;       
  syscall
  jmp   loop

; displays an error message
err:
  mov   rax, 1 ;           
  mov   rdi, 1 ;         
  mov   rsi, lblErr ;
  mov   rdx, lblErrLength ;       
  syscall
  jmp loop

; shutsdown program ; sys_write ; sys_exit
exit:
  mov   rax, 1 ;           
  mov   rdi, 1 ;         
  mov   rsi, lblByeBye ;
  mov   rdx, lblByeByeLength ;       
  syscall
  mov   rax, 60
  mov   rdi, 0
  syscall