loop-aarch64.s

.text
.globl _start

start = 0
max = 31

_start:
        mov     x28,start       /* loop index */

loop:

        /* Print msg */
        mov     x2, len         /* message length (bytes) */
        adr     x1, msg         /* message location (memory address) */
        mov     x0, 1           /* file descriptor: 1 is stdout */
        mov     x8, 64          /* write is syscall #64 */
        svc     0               /* invoke syscall */

        /* division */
        mov     x19, #10        /* r19 holds value of 10 */
        udiv    x20, x28, x19   /* x20 (quo) = x28 (li) / x19 (div) */
        msub    x21, x19, x20, x28 /* x21(rmdr) = x28(li) - ( x20(quo) * x19(div) ) */

        /* print leading digit */
        cmp     x20, #0         /* 0 - quotient */
        b.eq    lsd             /* if values are equal, jump to lsd (least significant digit) */

        mov     x2, len2
        adr     x1, digit
        add     x20, x20, #48
        str     x20, [x1]

        mov     x0, 1
        mov     x8, 64
        svc     0


lsd:
        /* Print following digit */
        mov     x2, len2        /* Length */
        adr     x1, digit       /* x1 holds address of digit */
        add     x21, x21, #48   /* ascii conversion */
        str     x21, [x1]       /* store ascii value on digit adr */

        mov     x0, 1
        mov     x8, 64
        svc     0


        /* Print newline */
        mov     x2, len1        /* message length (bytes) */
        adr     x1, nl          /* message location (memory address) */
        mov     x0, 1           /* file descriptor: 1 is stdout */
        mov     x8, 64          /* write is syscall #64 */
        svc     0               /* invoke syscall */

        /* loop condition */
        add     x19,x28,1
        mov     x28,x19         /* inc by adding 1 to counter */
        cmp     x28,max         /* max - counter */
        b.ne    loop            /* jump to loop if negative */
        
        /* exit */
        mov     x0, 0           /* status -> 0 */
        mov     x8, 93          /* exit is syscall #93 */
        svc     0               /* invoke syscall */

.data
msg:    .ascii      "Loop: "
len=    . - msg

nl:     .ascii      "\n"
len1=   . - nl

digit:  .ascii      " "
len2=   . - digit