fizzbuzz.asm

; to compile and run:
; nasm -f elf64 -l fizzbuzz.lst fizzbuzz.asm
; gcc -o fizzbuzz fizzbuzz.o
; ./fizzbuzz

        global main
        extern printf

        section     .text
main:
        mov         ecx, 0
        xor         rax, rax
print:
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;; print the number
        push        rax
        push        rcx

        mov         rdi, num_format
        mov         rsi, rcx
        xor         rax, rax

        call        printf

        pop         rcx
        pop         rax
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;; end print the number

        cmp         rcx, 0 ; We don't print fizzbuzz for zero, special case
        je          handle_newline

        push        rax
        push        rcx
        push        rdx

        xor         rdx, rdx
        mov         rax, rcx
        mov         rcx, 3
        idiv        rcx
        cmp         rdx, 0 ; should we display fizz?
        jne         dont_handle_fizz

        mov         rcx, rdx
        mov         rdi, fizz_format
        xor         rax, rax

        call        printf ; print fizz

dont_handle_fizz:
        pop         rdx
        pop         rcx
        pop         rax

        push        rax
        push        rcx
        push        rdx

        xor         rdx, rdx
        mov         rax, rcx
        mov         rcx, 5
        idiv        rcx
        cmp         rdx, 0 ; should we display buzz?
        jne         dont_handle_buzz
        mov         rcx, rdx
        mov         rdi, buzz_format
        xor         rax, rax

        call        printf ; print buzz
dont_handle_buzz:
        pop         rdx
        pop         rcx
        pop         rax

handle_newline:
        push        rax
        push        rcx

        mov         rdi, nl_format
        xor         rax, rax

        call        printf ; print newline either way

        pop         rcx
        pop         rax

        inc         ecx

        cmp         ecx, 101
        jne         print

        ret
num_format:
        db          "%20d", 9, 0 ; 9 = tab
fizz_format:
        db          "Fizz", 0
buzz_format:
        db          "Buzz", 0
nl_format:
        db          10, 0 ; 10 = \n newline