; nasm -f elf64 count.asm -o count.o
; ld count.o -o count
; ./count

BITS 64
SECTION .data
    prefix db "Line ", 0         ; constant prefix string
    newline db 10, 0             ; newline character "\n"

SECTION .bss
    numbuf resb 16               ; buffer to hold number string

SECTION .text
    global _start

;----------------------------------------
; _start: Entry point
;----------------------------------------
_start:
    mov r8, 1              ; counter (1 to 100)

print_loop:
    ; Print "Line "
    mov rsi, prefix
    call print_str

    ; Convert counter to string
    mov rax, r8
    mov rdi, numbuf
    call int_to_str

    ; Print number
    mov rsi, numbuf
    call print_str

    ; Print newline
    mov rsi, newline
    call print_str

    ; Increment and check loop condition
    inc r8
    cmp r8, 100
    jle print_loop

    ; Exit syscall
    mov rax, 60
    xor rdi, rdi
    syscall

;----------------------------------------
; print_str: rsi = null-terminated string
;----------------------------------------
print_str:
    push rsi
    mov rdi, rsi
    xor rcx, rcx
.find_len:
    cmp byte [rdi+rcx], 0
    je .got_len
    inc rcx
    jmp .find_len
.got_len:
    mov rax, 1          ; sys_write
    mov rdi, 1          ; fd = stdout
    mov rdx, rcx        ; length
    mov rsi, rsi        ; buffer
    syscall
    pop rsi
    ret

;----------------------------------------
; int_to_str: rax = number, rdi = buffer
; Converts integer in RAX to ASCII string
; (null-terminated, left-justified)
;----------------------------------------
int_to_str:
    mov rcx, 0
    mov rbx, 10

.int_div_loop:
    xor rdx, rdx
    div rbx             ; quotient in rax, remainder in rdx
    push rdx
    inc rcx
    test rax, rax
    jnz .int_div_loop

    ; Write digits to buffer
    mov rsi, rdi
.write_digits:
    pop rdx
    add dl, '0'
    mov [rsi], dl
    inc rsi
    loop .write_digits

    mov byte [rsi], 0   ; null terminator
    ret