Digits to text in Assembly

A number becomes printable by adding '0'.

; A number becomes text by adding '0' -- one digit at a time.
        global _start

        section .bss
buf:    resb 2

        section .text
_start:
        mov rax, 7              ; the digit to print
        add rax, '0'            ; 7 -> '7' (ASCII 55)
        mov [buf], al           ; store the low byte
        mov byte [buf + 1], 10  ; newline

        mov rax, 1
        mov rdi, 1
        mov rsi, buf
        mov rdx, 2
        syscall

        mov rax, 60
        xor rdi, rdi
        syscall

How it works

1. add rax, '0' turns 7 into ASCII 55.
2. mov [buf], al stores just the low byte.
3. One digit and a newline make a two-byte write.

Keywords and builtins used here

• add
• al
• byte
• global
• mov
• rax
• rdi
• rdx
• resb
• rsi
• section
• syscall
• xor

The run, in numbers

Lines

22

Characters to type

386

Tokens

62

Three-star pace

55 tpm

At the three-star pace of 55 tokens a minute, this run takes about 68 seconds.

Type this snippet

Step 1 of 3 in Talking to Linux, step 26 of 31 in Language basics.

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