Small Fizzbuzz

fizzbuzz_optimised.asm

.model tiny
.code

    org 0100h

start:

    ; initialise counters
    mov cl, 0

restart:
    mov si, offset circ

next_number:
    
    ; load next relative pointer from [circ] into AL 
    xor ax, ax
    lodsb

    ; before doing any printing, let's update the values in [number]
    adjust_number:
        mov di, offset number

        ; add "offset number" to ax to point di to start of string
        add ax, di

        ; DX = AX (used for printing later)
        mov dx, ax

        ; increase because we're 1-based not 0-based
        inc cx
    
    two_digits:
        ; first digit
        mov ax, cx
        mov bl, 10
        div bl

        add ax, 3030h

        ; first byte is '0'? replace with 'return'
        cmp al, 30h
        jne store_now

        mov al, 13

    store_now:

        stosw

    ; k, let's print whatever we're pointing at. 
    start_printing:

        mov ax, 0924h
        int 21h

        mov dx, offset newline
        int 21h

        cmp cl, 20
        je done

        cmp si, offset circ + 15
        je restart

    jmp next_number

done:

    ret


;     ____        _        
;    |  _ \  __ _| |_ __ _ 
;    | | | |/ _` | __/ _` |
;    | |_| | (_| | || (_| |
;    |____/ \__,_|\__\__,_|
;                          

    ; relative offsets of strings we can print
    number_start EQU 0
    fizz_start EQU 3
    buzz_start EQU 8
    fizzbuzz_start EQU 13

    number         db '  $'
    fizz         db 'Fizz$'
    buzz         db 'Buzz$'
    fizzbuzz     db 'FizzBuzz$'

    newline     db 13, 10, '$'

    ; pattern of finding fizzbuzz combinations
    circ:
        db number_start, number_start, fizz_start, number_start, buzz_start
         db fizz_start, number_start, number_start, fizz_start, buzz_start, number_start
         db fizz_start, number_start, number_start, fizzbuzz_start

END start