Number Counter

; Number Counter on Assembly

; Registers can be used
; ESI, EBP,

%macro PrintUnits 0

    mov eax, 4      ; sys_write
    mov ebx, 1      ; file descriptor (stdout)
    mov ecx, Units  ; Count register for string values
    mov edx, 1      ; 1 byte for 1 charactor
    int 0x80        ; call kernel
%endmacro

%macro PrintTens 0

    mov eax, 4      ; sys_write
    mov ebx, 1      ; file descriptor (stdout)
    mov ecx, Tens   ; Count register for string values
    mov edx, 1      ; 1 byte for 1 charactor
    int 0x80        ; call kernel
%endmacro

%macro PrintHundreds 0

    mov eax, 4          ; sys_write
    mov ebx, 1          ; file descriptor (stdout)
    mov ecx, Hundreds   ; Count register for string values
    mov edx, 1          ; 1 byte for 1 charactor
    int 0x80            ; call kernel
%endmacro

%macro Printnewline 0   ; Same as above prints
    mov eax, 4
    mov ebx, 1
    mov ecx, Newline
    mov edx, Nllen
    int 0x80
%endmacro

section .data
    Message: db 'Number Counter by UNIXnerdV 2022', 0xA, 0xA    ; String
    msglen: equ $-Message       ; length or size of string
    Newline: db '',0xA          ; Newline "\n"
    Nllen: equ $-Newline        ; Newline length

section .bss

    Units:   resb 1     ; 1 byte reserve
    Tens:    resb 1     ; 1 byte reserve
    Hundreds resb 1     ; same


section .text
    global _start


_start:
        mov esi, 48         ; Set to ASCII Value of 0 using code
        mov ebp, 48         ; same as above
        mov edi, 48         ; same

        mov eax, 4          ; sys_write
        mov ebx, 1          ; fd
        mov ecx, Message    ; String
        mov edx, msglen     ; Length
        int 0x80

        jmp print_units     ; start to display numbers jump to function

print_units:                    ; Print  Numbers

        mov [Units], esi    ; move values Units variable from ESI (Source Index)
        mov [Tens], ebp     ; move values Tens variable from ESI (Base)
        mov [Hundreds],edi  ; move values Hundreds variable from EDI (Destination Index)

        ; Print Numbers
        PrintHundreds       ; Print Hundreds column
        PrintTens           ; Print Tens column
        PrintUnits          ; Print Units column
        Printnewline        ; Newline "\n"


        inc esi             ; Increment Unit's register
        cmp esi, 57         ; Compare if matches ASCII value of 57 (Number 9)
        jle print_units     ; jump less equal to start of function
        cmp esi, 57         ; compare again
        je _inc_tens        ; if equals jump to increment tens

_inc_tens:                          ; Increments the tens
    mov esi, 48                     ; Reset previous register to 0
    inc ebp                         ; increment ten's register
    mov [Tens], ebp                 ; save value to variabe

    cmp ebp, 57                     ; compare for number 9 (57)
    jle print_units                 ; start at beginning

    cmp ebp, 57                     ; compare again
    je _inc_hundreds                ; if match jump to hundreds

_inc_hundreds:                      ; Increment Hundreads
    mov ebp, 48                     ; Reset Previous register to 0
    inc edi                         ; increment hundreds register
    mov [Hundreds], edi             ; save

    cmp edi, 57                     ; compare
    jle print_units                 ; start again if does not reach 9

    cmp edi, 57                     ; compare again
    je _sysexit                     ; quits if reaches 9 (57)


_sysexit:
    mov eax, 1          ; System exit (exit(0) in C)
    mov ebx, 0          ; Exit code 0
    int 0x80            ; omitting this will cause a seg fault