ass 4 HEX to BCD part2

;ALP program to convert HEX to BCD
;--------------------------------------------------

section .data

msg1 db "Enter 4 digit HEX number:"
msg1_len equ $-msg1

msg2 db "Converted into Decimal number:"
msg2_len equ $-msg2

emsg db "Invalid BCD number"
emsg_len equ $-emsg

;-----------------------------------------------------------

section .bss

buf resb 2
ans resb 2
char_ans resb 2

%macro print 2
mov rax,1
mov rdi,1
mov rsi,%1
mov rdx,%2
syscall
%endmacro

%macro read 2
mov rax,0
mov rdi,0
mov rsi,%1
mov rdx,%2
syscall
%endmacro

%macro exit 0
mov rax,60
mov rdi,0
syscall
%endmacro
;----------------------------------------------------------

section .text
global _start
_start:

Call HEX_BCD
exit

HEX_BCD:
print msg1,msg1_len
read buf,5
mov rcx,4
mov rsi,buf
mov bx,0

next_byte:
shl bx,4
mov al,[rsi]

cmp al,'0'
JB error
cmp al,'9'
JBE sub30

cmp al,'A'
JB error
cmp al,'F'
JBE sub37

cmp al,'a'
JB error
cmp al,'f'
JBE sub57

error:
print emsg,emsg_len
exit

sub57 : sub al,20h
sub37 : sub al,07h
sub30 : sub al,30h

Add bx,ax

INC rsi
DEC rcx
JNZ next_byte

print msg2,msg2_len
mov ax,bx
Call Display
ret

Display:
mov rbx,10
mov rcx,4
mov rsi,char_ans+3

back:
mov rdx,0
div rbx

cmp dl,09h
jbe add30
add dl,07h

add30:
add dl,30h

mov [rsi],dl
dec rsi
dec rcx
jnz back

print char_ans,4
ret