x86 - Find and display greatest common divisor from 2 input numbers in nasm -


good day,

i have been trying write program following:

  1. accept 2 ascii numbers user (i haven't bothered trying check values yet)
  2. convert ascii numbers decimal values.
  3. find greatest common divisor 2 numbers
  4. display result

i feel though i've done steps 1-3, although i'm not entirely sure. here code: 

bits 16 org 0x100; jmp main ;  number1_str: db 3,0,0,0,0,'$' number2_str: db 3,0,0,0,0,'$' num1_hex: dw 2 num2_hex: dw 2  prompt1: db 'please enter first number (from 1 50): ','$' prompt2: db 'please enter second number (from 1 50): ','$'  cr_lf:      db 13,10,'$'   ; carriage return , line feed  ; ;displays string in dx ; disp_str:      mov ah,09              ;     int 0x21               ;     ret                ;  ; ; converts ascii string of digits decimal number, , puts result ; in ax, , passes address dx. if error occurs, al set 'e'. ; str_to_num:     xor ax,ax              ; initial value of ax = 0     xor bh,bh              ;                  bh = 0     mov cx,10              ; build integer in ax (multiply 10)     mov si,dx              ; dx points start of input buffer     call next_char         ;       ret                ; next_char:     mov bl,[si]            ; move contents of memory pointed si bl     cmp bl,0x0d    ; carriage return?     je finis               ; yes, done     cmp bl,0x39            ; ascii character '9' 39h     jg  error              ; > '9', invalid character     sub bl,0x30            ; convert numeric value (ascii '0' - 30h)     jl error               ; < 0, invalid character     imul cx        ; dx:ax = ax * 10 (32-bit result)     add ax,bx              ; add next digit     inc si                 ; pointer next char     jmp next_char      ; repeat next character     ret                ; error:      mov al,'e'             ; flag error finis:     ret                ; return calling program  ; ;calculates greatest common divisor values in ;ax , bx. gcd stored in ax. ; gcd:     idiv bx         ; remainder (7) in dx, quotient (1) in ax     mov ax,bx               ; move bx ax     mov bx,dx               ; move dx bx     cmp bx, 0x0     ; y = 0?     jg yiszero              ; y zero, return call main     call gcd                ; loop again if y isn't 0 ; ; displays result in ax , terminates program ; yiszero:     xor dx,dx              ; set dx 0     add ax,0x30    ; convert remainder ascii, store in ax     mov dx,ax              ;     int 0x21               ;     int 0x20               ; terminate program   main:     mov dx,prompt1     ; move prompt1 dx     call disp_str              ; display prompt1      ;get number1_str     xor dx,dx              ; set dx 0     mov ah,0x0a    ; accept string user     mov dx,number1_str; address string     int 0x21               ;          call str_to_num    ;     mov [num1_hex],ax ; put value of ax contents of memory address @                         ; num1_hex      mov ah,09              ; display string     mov dx,cr_lf       ; display carriage return , line feed     int 0x21               ;      mov dx,prompt2     ; move prompt2 dx     call disp_str      ; display prompt2      ;get number2     xor dx,dx              ; set dx 0     mov ah,0x0a    ; accept string user     mov dx,number2_str; address string     int 0x21               ;      call str_to_num    ;     mov [num2_hex],ax ; put value of ax contents of memory address @                         ; num2_hex      mov ah,09              ; display string     mov dx,cr_lf       ; display carriage return , line feed     int 0x21               ;      ; find greatest common divisor     xor dx,dx              ; set dx 0     mov ax,num1_hex   ; move value in num1_hex ax     mov bx,num2_hex   ; move value in num2_hex bx     call gcd               ; find greatest common divisor values in ax , bx

i'm expecting y_is_zero display result, wait entry when run code above. if press key, program ends. i

any appreciated. - js

gdc not appear attempt display anything; never calls disp_str, , system call makes (before 1 exit program) not match 1 in subroutine.


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