fasm_3_1_v2

org 100h

        NL_ equ $d, $a ; new line

        mov ah, $9
        mov dx, helloStr_
        int 21h

        mov dx, inputA_
        int 21h

        mov ah, $a ; input to buff
        mov dx, buffNum
        int 21h

        add dx, 2 ; dx = adress of first char in str
        call str_to_int_ ; input dx - str with '$' in the end
                         ; output al - 8 bit number
        mov bh, al ; bh = A

        mov ah, $2 ; new line
        mov dx, $0d0a
        int 21h

        mov ah, $9 ; output - inputStr
        mov dx, inputB_
        int 21h

        mov ah, $a ; input to buff
        mov dx, buffNum
        int 21h

        add dx, 2 ; get second number
        call str_to_int_

        mov dl, al ; save second to dl
        mov dh, bh ; move first to dh

        call task_ ; input dh - A, dl - B, output ax - 16 bit number

        mov dx, buffAns
        call int_to_str_ ; input ax - 16 bit number, dx - 6 byte buffer; output - string
                         ; representation of number in buff that ends with $

        mov ah, $9 ; output - resultStr
        mov dx, resultStr_
        int 21h

        mov dx, buffAns ; output - buffAns
        int 21h

        mov dx, byeStr_ ; output - byeStr
        int 21h

        mov ah, $8 ; wait for input
        int 21h
        ret

str_to_int_: ; input dx - string that ends on 0dh; output al - 8bit number
        push cx
        push bp
        mov bp, sp
        sub sp, 1 ; one byte for const base
        mov byte [bp-1], 10 ; const 10 (base)
        push bx ; save
        mov bx, dx ; memory accessible only from bx
        xor ax, ax ; clear ax
        next_digit_:
                mul byte [bp-1] ; *10, result ax
                mov cl, [bx]
                sub cl, '0' ; char to digit
                add al, cl ; add new digit
                inc bx ; move to next symbol
        cmp byte [bx], $d ; char > 13 ?
        jne next_digit_ ; if no then there're still numbers to convert left
        pop bx ; retrieve
        mov sp, bp ; stack...
        pop bp
        pop cx
        ret ; go back

int_to_str_: ; input ax - 16 bit number, dx - buffer (string with length of 6); output - string representation of number in buff that ends with $
        push ax ; save ...
        push dx
        push bx
        push bp ; stack...
        mov bp, sp
        sub sp, 2 ; reserve 2 bytes
        mov word [bp-2], 10 ; const 10 2 byte
        mov bx, dx ; address of buff to bx
        xor dx, dx ; clear dx
        push '*' ; "stopper" for string conversation
        push '$' ; last symbol

        next_letter_:
                div word [bp-2] ; divide dx:ax by 16bit number; result dx-remainder, ax-quotient
                add dx, '0' ; convert to ascii number
                push dx ; save symbol to stack
                xor dx, dx ; clear dx
                cmp ax, 0 ; have we converted whole number?
                jne next_letter_ ; if no there're still number to convert

        next_save_letter_:
                pop dx ; get symbol
                cmp dx, '*' ; is stopper?
                je exit_int_to_str_ ; if yes - exit
                mov [bx], dl ; if no move to buffer
                inc bx ; go to next symbol address
                jmp next_save_letter_ ; next letter
        exit_int_to_str_:
                mov sp, bp ; return stack pointer to its original state
                pop bp ; retrieve
                pop bx
                pop dx
                pop ax
        ret ; go back

task_: ; input
                ; dh - A
                ; dl - B
       ; output ax
       xor ax, ax ; clear ax
       mov al, dh ; A to al
       mul al ; *A
       xor bh, bh
       mov bl, dl
       xor dx, dx
       div bx ; (dx:ax)/B, mod in dx
       add ax, bx ; +B
       ret ;go back

helloStr_ db "This program calculates the result of a*a/b+b", NL_, "Using register type procedure", NL_, "$"
inputA_ db "Input number in range from 0 to 255:", NL_, "$"
inputB_ db "Input number in range from 1 to 255:", NL_, "$"
resultStr_ db NL_, "Result:", NL_, "$"
byeStr_ db NL_, "Press anything to terminate a program...$"
buffNum db 6, 0, 6 dup(?)
buffAns db 6 dup (?)