More efficient way to output an integer in pure assembly

Question

I\'m looking to output an integer using pure assembly. I\'m using nasm on a 64-bit linux machine. At the moment I\'m looking for a way to output integers to debug a compiler

Answer 1

Here are some possible changes to the routine:

_printi:
    pushf
    push    rax
    push    rbx
    push    rcx
    push    rdx

    mov rax, [rsp+48]
    mov rcx, 4
    mov rbx, 10 ; --moved outside the loop
.start:
    dec rcx
    xor rdx, rdx
    div rbx
    add rdx, 48
    mov [var+rcx], dl
    cmp rax, 0
    jne .start

    ; mov rax, [var] -- not used
    ; push    rax -- not used
    call    _printc
    ; pop rax -- not used

    pop rdx
    pop rcx
    pop rbx
    pop rax
    popf
    ret

I also noted some limitations in the algorithm. If the number is larger than 9999, the code will continue to put digits outside of the allocated space, overwriting some other data. The routine is not fully reusable, i.e. if you print 123, then 9 it will come out as 129.