ASCII to HEX and display again, Assembly

ASCII to HEX and display again

;nasm 2.13.02

section .data
    m1 db 'Enter 2 digit number',10d,13d         ; 10D is line feed(new line)and 13D(set cursor) is carriage return
    l1 equ $-m1    
    m2 db 'The 2 digit number is=',10d,13d
    l2 equ $-m2
    m3 db " ",10d,13d                           ; Declared for spaces
    l3 equ $-m3
    
    %macro read_write 4
    mov rax,%1      ; Function for sys_write     
	mov rdi,%2      ; File descriptor id for i/o
	mov rsi,%3      ; Memory address of m1
	mov rdx,%4      ; count of bytes to be displayed
    syscall         ; call kernel
    %endmacro
   
    
section .bss  ; block starting symbol for uninitialized var
    num RESB 20 ; Reserve 20 bytes for num variable 
    array RESB 200
    char_ans RESB 16

section .text
	global _start

_start:
	
    read_write 1,1,m1,l1
    read_write 0,0,num,3  ; 0 and 0 for read function and 3 because 2 numbers and the enter hit on keyboard
    
    call accept_proc   ; here the subroutine is called
    mov rbp,array      
    mov [rbp],bx
    
    
    read_write 1,1,m2,l2
    mov ax,bx
    call display_proc
    
    read_write 1,1,num,16
    
    mov rax,60     ; Function no for sys_exit
	mov rdi,0      ; return 0             
	syscall
    
    
accept_proc:
         mov rsi,num  ; point the rsi to the first number
         mov rbx,0    ; set it to 0
         mov rax,0    ; set it to 0
         mov rcx,2    ; counter for the 2 numbers ( To keep a count of how many digits have been converted
back:
         rol rbx,04    ; Rotate the bits to left by 4 as after the first digit is converted using whole subroutine, the number is at unit postion so to get it a ten's postion rotate by 4
         mov al,[rsi]  ; move the content of rsi to al
         cmp al,39h    ; compare with 39h becaue after 39h there are special characters in ascii table for hex
         jbe next      ; jump if below or equal after comaparing 
         sub al,07h    ; subtract 07h from the number if greater than 39h as 7 special characters in between
         
next: 
        sub al,30h     ; Subtract 30h from al
        add bx,ax      ; add contents of ax to bx
        inc rsi        ; increment rsi that is now point to next number 
        dec rcx        ; decrement the counter 
        jnz back       ; if counter not zero then go the back
ret

display_proc: 
       mov rbp,char_ans
       mov rcx,2
  
up3:   
       rol al,04
       mov dl,al
       
       and dl,0Fh
       
       cmp dl,09h
       jbe next1
       
       add dl,07h
     
next1:
       add dl,30h
       
       mov[rbp],dl
       
       inc rbp
       dec rcx
       
       jnz up3
       
       read_write 1,1,char_ans,16
       
       read_write 1,1,m3,l3


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