Assembly x64 Intro - Nasm Fibinachi Numbers Implementation

; fib_64l.asm  using 64 bit registers to implement fib.c
 global main
 extern printf

 section .data
format: db '%15ld', 10, 0
title: db 'fibinachi numbers', 10, 0
 
 section .text
main:
 push rbp   ; set up stack
 mov rdi, title   ; arg 1 is a pointer
 mov rax, 0   ; no vector registers in use
 call printf

 mov rcx, 95   ; rcx will countdown from 52 to 0
 mov rax, 1   ; rax will hold the current number
 mov rbx, 2   ; rbx will hold the next number
print:
 ;  We need to call printf, but we are using rax, rbx, and rcx.
 ;  printf may destroy rax and rcx so we will save these before
 ;  the call and restore them afterwards.
 push rax   ; 32-bit stack operands are not encodable
 push rcx   ; in 64-bit mode, so we use the "r" names
 mov rdi, format  ; arg 1 is a pointer
 mov rsi, rax   ; arg 2 is the current number
 mov eax, 0   ; no vector registers in use
 call printf
 pop rcx
 pop rax
 mov rdx, rax   ; save the current number
 mov rax, rbx   ; next number is now current
 add rbx, rdx   ; get the new next number
 dec rcx   ; count down
 jnz print   ; if not done counting, do some more

 pop rbp   ; restore stack
 mov rax, 0  ; normal exit
 ret