ASM Program to Convert Hex to BCD [MP Part1]

Problem Statement: 

Write X86/64 ALP to convert 4 - digit Hex number into its equivalent BCD number and 5 - digit BCD n umber into its equivalent HEX number. Make your program user friendly to accept the choice from user for:
(a) HEX to BCD
b) BCD to HEX [ Included in Program]
 (c) EXIT. Display proper strings to prompt the user while accepting the input and displaying the result. (wherever necess ary, use 64 - bit registers)

Code:-

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%macro scall 4 ;macro to take input and output mov rax,%1 mov rdi,%2 mov rsi,%3 mov rdx,%4 syscall %endmacro Section .data msg1: db "Enter 4 Digit HEX Number: ",0x0A len1: equ $-msg1 msg2:db "BCD Number : " len2: equ $-msg2 cnt :db 00H Section .bss ans resw 8 num resb 8 Section .text global main main: scall 1,1,msg1,len1 scall 0,0,num,8 mov rsi,num call AtoH mov rax,rbx mov rbx,000AH mov rdi,ans+7 loop: mov rdx,0 div rbx add dl,30h mov [rdi],dl dec rdi cmp rax,0 jne loop scall 1,1,msg2,len2 scall 1,1,ans,8 ;add rax,30 ;mov word[ans],ax ;dec cx ;jnz ploop ;scall 1,1,ans,8 mov rax,60 mov rdi,0 syscall AtoH: ;result hex no is in bx mov byte[cnt],04H mov ebx,00H hup: rol ebx,04 mov al,byte[rsi] cmp al,39H JBE HNEXT SUB al,07H HNEXT: sub al,30H add bl,al INC rsi DEC byte[cnt] JNZ hup ret

Output: