compare.s

.global _main
.align 2

.data
guess_msg:    .ascii "INPUT A NUMBER (0-9):"
guess_len =   . - guess_msg
equal_msg:    .ascii "BOTH NUMBERS ARE EQUAL!\n"
equal_len =   . - equal_msg
lower_msg:    .ascii "FIRST NUMBER IS HIGHER!\n"
lower_len =   . - lower_msg
higher_msg:   .ascii "SECOND_NUMBER IS HIGHER!\n"
higher_len =  . - higher_msg
error_msg:    .ascii "INVALID INPUT! MUST INPUT 0-9!\n"
error_len =   . - error_msg
buffer:       .space 2

.text
_main:
  mov x20, #0
  mov x21, #0
  mov x22, #0

ReadNumber:
  ; Prompt for a number
  mov  x0,  #1                ; stdout
  adrp x1,  guess_msg@PAGE
  add  x1,  x1,  guess_msg@PAGEOFF
  mov  x2,  guess_len
  mov  x16, #4                ; write
  svc  #0x80

  ; Read the number
  mov  x0,  #0                 ; stdin
  adrp x1,  buffer@PAGE
  add  x1,  x1,  buffer@PAGEOFF
  mov  x2,  #2                 ; read digit & newline
  mov  x16, #3                 ; read
  svc  #0x80

  ; Reload buffer address, clobbered by syscall
  adrp x1,  buffer@PAGE
  add  x1,  x1,  buffer@PAGEOFF

  ; Convert input to digit
  ldrb w20, [x1]               ; load the first byte
  sub  w20, w20, #48           ; subtract 48 (ASCII 0)

  ; Ensure input is within range 0-9
  cmp  w20, #0
  b.lt OutOfRange
  cmp  w20, #9
  b.gt OutOfRange

  add  x22, x22, #1
  cmp  x22, #2                ; do we have 2 numbers?
  b.eq Compare

  mov  w21, w20               ; put our first number in x21 so 2nd run
                              ; doesn't clobber it
  b    ReadNumber

Compare:
  cmp  w20, w21               ; compare user input to our random number
  b.lt Lower                  ; prompt the user to guess higher
  b.gt Higher                 ; prompt the user to guess lower
  b    Equal

Higher:
  ; Second number is higher
  adrp x1,  higher_msg@PAGE
  add  x1,  x1,  higher_msg@PAGEOFF
  mov  x2,  higher_len
  b    PrintAndExit

Lower:
  ; First number is higher
  adrp x1,  lower_msg@PAGE
  add  x1,  x1,  lower_msg@PAGEOFF
  mov  x2,  lower_len
  b    PrintAndExit

Equal:
  ; Numbers Are Equal
  adrp x1,  equal_msg@PAGE
  add  x1,  x1,  equal_msg@PAGEOFF
  mov  x2,  equal_len

PrintAndExit:
  mov  x0,  #1                ; stdout
  mov  x16, #4                ; write
  svc  #0x80

  ; Exit with status 0
  mov x0,  #0
  mov x16, #1
  svc #0x80

OutOfRange:
  ; Prompt the user for a valid input
  mov  x0,  #1                ; stdout
  adrp x1,  error_msg@PAGE
  add  x1,  x1,  error_msg@PAGEOFF
  mov  x2,  error_len
  mov  x16, #4                ; write
  svc  #0x80
  b    ReadNumber