STDIN:      EQU     0
STDOUT:     EQU     1
STDERR:     EQU     2

SYS_READ:   EQU     0
SYS_WRITE:  EQU     1

section .data
        PRINT_ENDL db `\n`,0

section .bss

        PRINT_INT_buffer resb 16

section .text
global PRINT_INT
global PRINT_NEWLINE
global PRINT_STRING

; rdi will hold the address of the string to print
; rsi will hold the length of the string to print
PRINT_STRING:
    mov rdx, rsi
    mov rsi, rdi
    mov rax, STDOUT
    mov rdi, SYS_WRITE

    syscall
    ret

PRINT_NEWLINE:
    mov eax, SYS_WRITE
    mov edi, STDOUT      ; set the destination to stdout
    mov esi, PRINT_ENDL
    mov edx, 2 
    syscall

    ret

PRINT_INT:

; this is a leaf routine, so we don't need to mess with the stack.
; Parameter:   rdi, the number to print

    mov rax, rdi

    mov [PRINT_INT_buffer+15], byte 0
    lea edi, [PRINT_INT_buffer + 14]

PRINT_INT_convert:
    dec edi                ; edi  scratch
    mov edx, 0             ; edx  scratch
    mov ecx, 10            ; ecx  scratch
    div ecx                ; eax = edx:eax/ecx edx = edx:eax%ecx
                           ; carter page 44
    add dl, '0'            ; dl + '0'   add ascii 0 to the digit
    mov [edi], dl          ; store the new character in edi buffer[14] = digit
    test eax, eax          ; check for any bits of eax not zero
                           ; carter page 51
    jnz PRINT_INT_convert

    mov esi, edi           ; esi needs the start position of the string.
                          
    lea edx, [PRINT_INT_buffer+14] ; edx needs the length of the string
                         ; the last character in the buffer.
    sub edx, edi         ; starting poisition - end position

    mov eax, SYS_WRITE
    mov edi, STDOUT      ; set the destination to stdout

    syscall

    ret