.text
  .align  2
  .global replace
  .type replace, %function

@ r0  first word
@ r1  second word
@ r2  third word

@ r3  first word letter
@ r4  second word letter
@ r5  third word letter

@ r6  i iterator
@ r7  j iterator


replace:
  MOV r6, #0 @ i = 0


first_iteration:
  MOV r7, #0 @ j = 0

  @ get the letter from first word
  LDRB r3, [r0, r6]

  CMP r3, #0 @ Last letter \0
  BEQ exit @ the the word was fully processed


second_iteration:
  @ get the letter from second word
  LDRB r4, [r1, r7]

  @ If second word ended exit second iteration
  CMP r4, #0
  BEQ first_iteration_increase

  @ If letters from both words are equal
  @ Grab and replace in first word
  CMP r3, r4
  BEQ swap_letters


second_iteration_increase:
  ADD r7, r7, #1 @move by byte
  B second_iteration


first_iteration_increase:
  ADD r6, r6, #1 @move by byte
  B first_iteration


swap_letters:
  LDRB r5, [r2, r7] @takes the letter to replace
  STRB r5, [r0, r6] @ replaces letter in w1

  B first_iteration_increase


exit:
  BX lr