fizzbuzz in nasm assembly

README.md

asm fizzbuzz

just a fun exercise for learning some x86_64 nasm assembly (linux)

you can run the code here

fizzbuzz.asm

section .data
    fizz_str: db "fizz"  ; string for "fizz"
    buzz_str: db "buzz"  ; string for "buzz"
    newline: db 10       ; ascii value for newline
    count_to: equ 100    ; count to 100

section .bss
    num_buffer: resb 3  ; buffer for number

section .text
    global _start

_start:
    xor r8, r8  ; initialize counter to 0

main_loop:
    inc r8          ; increment counter
    xor r9, r9      ; initialize flag to 0
    mov rdx, 0      ; clear remainder register
    mov rax, r8     ; copy counter to dividend register
    mov rcx, 3      ; divisor for fizz
    div rcx         ; divide by 3
    cmp rdx, 0      ; check if remainder is 0
    jnz check_buzz  ; if not, jump to check_buzz
    or r9, 1        ; if yes, set flag to 1

check_buzz:
    mov rdx, 0          ; clear remainder register
    mov rax, r8         ; copy counter to dividend register
    mov rcx, 5          ; divisor for buzz
    div rcx             ; divide by 5
    cmp rdx, 0          ; check if remainder is 0
    jnz process_number  ; if not, jump to process_number
    or r9, 2            ; if yes, set flag to 2

process_number:
    cmp r9, 0          ; check if flag is 0
    jnz process_fizz   ; if not, jump to process_fizz
    mov rax, r8        ; copy counter to dividend register
    call print_number  ; call print_number
    jmp check_end      ; jump to check_end

process_fizz:
    cmp r9, 1         ; check if flag is 1
    jnz process_buzz  ; if not, jump to process_buzz
    call print_fizz   ; call print_fizz
    jmp check_end     ; jump to check_end

process_buzz:
    cmp r9, 2             ; check if flag is 2
    jnz process_fizzbuzz  ; if not, jump to process_fizzbuzz
    call print_buzz       ; call print_buzz
    jmp check_end         ; jump to check_end

process_fizzbuzz:
    call print_fizzbuzz  ; call print_fizzbuzz

check_end:
    cmp r8, count_to   ; check if counter reached count_to
    je exit_program    ; if yes, jump to exit_program
    jmp main_loop      ; if not, jump to main_loop

print_fizzbuzz:
    mov rbx, 1      ; set flag to 1 to indicate fizzbuzz
    jmp print_fizz  ; jump to print_fizz

print_fizz:
    xor rbx, rbx  ; clear flag

print_fizz_continue:
    mov rax, 1         ; syscall number for write
    mov rdi, 1         ; file descriptor 1 is stdout
    mov rsi, fizz_str  ; pointer to fizz_str
    mov rdx, 4         ; string length
    syscall            ; call kernel
    cmp r9, 3          ; check if flag is 3 (fizzbuzz)
    jne print_newline  ; if not, jump to print_newline
    jmp print_buzz     ; if yes, jump to print_buzz

print_buzz:
    mov rax, 1         ; syscall number for write
    mov rdi, 1         ; file descriptor 1 is stdout
    mov rsi, buzz_str  ; pointer to buzz_str
    mov rdx, 4         ; string length
    syscall            ; call kernel
    jmp print_newline  ; jump to print_newline

print_newline:
    mov rax, 1        ; syscall number for write
    mov rdi, 1        ; file descriptor 1 is stdout
    mov rsi, newline  ; pointer to newline
    mov rdx, 1        ; string length
    syscall           ; call kernel
    ret               ; return from subroutine

print_number:
    mov r9, 2  ; set flag to 2

convert_to_ascii:
    mov rdx, 0               ; clear remainder register
    mov rcx, 10              ; divisor for conversion
    div rcx                  ; divide
    add rdx, 0x30            ; convert to ASCII
    mov [num_buffer+r9], dl  ; store in buffer
    dec r9                   ; decrement flag
    cmp rax, 0               ; check if dividend is 0
    jnz convert_to_ascii     ; if not, jump to convert_to_ascii
    mov rax, 1               ; syscall number for write
    mov rdi, 1               ; file descriptor 1 is stdout
    mov rsi, num_buffer      ; pointer to num_buffer
    mov rdx, 3               ; string length
    syscall                  ; call kernel
    call print_newline       ; call print_newline
    ret                      ; return from subroutine

exit_program:
    mov rax, 60   ; syscall number for exit
    xor rdi, rdi  ; exit code 0
    syscall       ; call kernel