%include "IO_DEFS.asm"

section .data
    num dd 24601   ; we will discuss db soon, but this does num = 42

section .bss
    buffer resb 16  ; this rese r ves 16 bytes (or characters)
                    ; the same as char buffer[16] in c.

section .text
    global _start

; data dictionary
;  All work is done in 32 bit registers.
;    eax holds the number to be printed, or some version of it.
;    edi holds the address of the buffer where we will store the number
;    edx and ecx are used for temporary computations.
;         edx is the digit just removed fom eax
;          dl will contain the character we are interested in
;         ecx is 10
;     
;   num = 24601;
;   char buffer[16]
;   buffer[16] = 0x0A   (or '\n')  
;   (pos = 15)
;   while (num > 0) {
;      digit = num % 10
;      num = num / 10
;      buffer[pos] = static_cast<char>(digit + '0')
;      (--pos)
;   }

_start:
    mov eax, [num]         ; load the number from memory
    lea edi, [buffer + 15] ; load effective address, base address + 15
                           ; edi = buffer+15 
                           ; Carter 93.
    mov byte [edi], 0x0A   ; newline character  buffer[15] = '\n'
                           
convert:
    dec edi                ; edi--  Carter page 23
    mov edx, 0             ; edx = 0
    mov ecx, 10            ; ecx = 10
    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 convert

    ; *****************************************************************
    ; Print the result
    ; *****************************************************************

    ; remember, at this point edi holds the last position we wrote to.
    ;     or the start of the string in the buffer.
    ;     this will vary based on the number of digits

    mov esi, edi         ; edi needs the start position of the string.
                          
    lea edx, [buffer+16] ; 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

    ; Exit
    mov eax, SYS_EXIT
    mov edx, SUCCESS 
    syscall