101 lines
2.1 KiB
NASM
101 lines
2.1 KiB
NASM
; nasm -f elf64 count.asm -o count.o
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; ld count.o -o count
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; ./count
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BITS 64
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SECTION .data
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prefix db "Line ", 0 ; constant prefix string
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newline db 10, 0 ; newline character "\n"
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SECTION .bss
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numbuf resb 16 ; buffer to hold number string
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SECTION .text
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global _start
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;----------------------------------------
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; _start: Entry point
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;----------------------------------------
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_start:
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mov rcx, 100 ; use rcx / loop as an easy counter.
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print_loop:
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; Print "Line "
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mov rsi, prefix
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call print_str
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; Convert counter to string
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mov rax, 101 ; as the rcx couns backwards we have to subtract it from 100 to have ascending order
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sub rax, rcx
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mov rdi, numbuf
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call int_to_str
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; Print number
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mov rsi, numbuf
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call print_str
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; Print newline
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mov rsi, newline
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call print_str
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loop print_loop ; will automatically decrement rcx and stop looping if it's 0
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; Exit syscall
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mov rax, 60
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xor rdi, rdi
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syscall
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;----------------------------------------
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; print_str: rsi = null-terminated string
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;----------------------------------------
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print_str:
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mov r8, rcx
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push rsi
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mov rdi, rsi
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xor rcx, rcx
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.find_len:
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cmp byte [rdi+rcx], 0
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je .got_len
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inc rcx
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jmp .find_len
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.got_len:
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mov rax, 1 ; sys_write
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mov rdi, 1 ; fd = stdout
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mov rdx, rcx ; length
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mov rsi, rsi ; buffer
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syscall
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pop rsi
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mov rcx, r8
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ret
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;----------------------------------------
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; int_to_str: rax = number, rdi = buffer
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; Converts integer in RAX to ASCII string
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; (null-terminated, left-justified)
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;----------------------------------------
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int_to_str:
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mov r8, rcx
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mov rcx, 0
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mov rbx, 10
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.int_div_loop:
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xor rdx, rdx
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div rbx ; quotient in rax, remainder in rdx
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push rdx
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inc rcx
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test rax, rax
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jnz .int_div_loop
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; Write digits to buffer
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mov rsi, rdi
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.write_digits:
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pop rdx
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add dl, '0'
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mov [rsi], dl
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inc rsi
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loop .write_digits
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mov byte [rsi], 0 ; null terminator
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mov rcx, r8
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ret
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