Number Printing

Printing Multi-Digit Numbers

Until now, we've only printed single-digit numbers by adding 48 ('0'). But what about larger numbers like 2048? We need to convert each digit to its ASCII character.

The Divide-by-10 Algorithm

To extract digits from a number, repeatedly divide by 10. The remainder gives the last digit, and the quotient gives the remaining number:

2048 / 10 = 204 remainder 8
 204 / 10 = 20  remainder 4
  20 / 10 = 2   remainder 0
   2 / 10 = 0   remainder 2

The digits come out in reverse order (8, 4, 0, 2), so we fill a buffer from right to left.

Computing a Remainder

ARM64 has no modulo operator, but remainder = n - (n/10) * 10:

MOV X1, #10
UDIV X2, X0, X1        // quotient = n / 10
MUL X3, X2, X1         // quotient * 10
SUB X3, X0, X3         // remainder = n - quotient * 10
ADD X3, X3, #48        // convert to ASCII digit

Filling from Right to Left

Start at the end of the buffer. Store each digit and move the pointer backward:

LDR X5, =buf
ADD X5, X5, #10       // Start near end

digit_loop:
    // ... compute remainder digit ...
    STRB W3, [X5]     // Store digit
    SUB X5, X5, #1    // Move left
    MOV X0, X2        // n = quotient
    CBNZ X0, digit_loop

After the loop, X5 + 1 points to the first digit.

Your Task

Print the number 2048 followed by a newline. Use the divide-by-10 approach to convert the number to its ASCII digits, store them in a buffer, then print.