replaceChar:
  pushq %rbp # setup
  movq %rsp,%rbp # setup
    subq $pointerSize, %rsp # get some space in the stack
    pushq %rdi # save to pointer value into the satck
  movb $0, %r8b # set r8 as loop index
  movb (%rdi), %r11b # r11 is the amount of chars in the string
  leaq 4(%rdi), %rdi # increase the pointer (move fowerd to the string)
.loopStart:
  cmpb %r8b, %r11b # check the loop index
  je .replaceAfterLoop
  cmpb (%rdi), %sil # check if need to replace
  je .replaceChar
.loopEnd:
  inc %rdi # increase the pointer value
  inc %r8b # increase the loop index value
  jmp .loopStart
.replaceChar:
  movb %dl,(%rdi) # replace the char
  jmp .loopEnd
.replaceAfterLoop:
    popq %rax # restore the value of pointer into the return value
  movq %rbp, %rsp # leave
  popq %rbp # leave
  ret