%macro scall 4          ;general macro with 4 parameters
        mov rax,%1
        mov rdi,%2
        mov rsi,%3
        mov rdx,%4
        syscall         ;call the kernel (interrupt)           
%endmacro

section .data
        menu db 10d,13d,"              MENU"
             db 10d,"1. Enter the String"
             db 10d,"2. Calculate Length of the string"
             db 10d,"3. Reverse String"
             db 10d,"4. Check Palindrome"
             db 10d,"5. Exit"
             
        menulen equ $-menu
        
        m1 db 10d,"Enter String: "
        l1 equ $-m1
        m2 db 10d,"Length Of String: "
        l2 equ $-m2
        m3 db 10d,"Reversed String: "
        l3 equ $-m3
        m4 db 10d,"String is Palindrome!!!"
        l4 equ $-m4
        m5 db 10d,"String is not Palindrome!!!"
        l5 equ $-m5
        
section .bss
        
        string resb 50
        string2 resb 50
        length resb 16
        answer resb 16
        
section .text
        global _start
_start:
        
        scall 1,1,menu,menulen
       
  scall 1,1,m1,l1    ;Enter String: "
        scall 0,0,string,50 ;length is returned in rax
        mov [length],rax

        scall 1,1,m2,l2         ;Length Of String: 
        mov rax,[length]
        call display            ;call procedure

        call stringreverse      ;call procedure
        
        scall 1,1,m3,l3     ;"Reversed String: "
        scall 1,1,string2,[length]

        mov rsi,string
  mov rdi,string2
  mov rcx,[length]
  
loop3:  
  mov al,[rsi]    ;MADAM
  cmp al,[rdi]     ;MADAM
  jne skip2

  inc rsi
  inc rdi
  dec byte[length]
  jnz loop3
  
  scall 1,1,m4,l4    ;String is Palindrome!!!"
  jmp exit
  
   skip2:
       scall 1,1,m5,l5  ;String is not Palindrome!!!"
   
exit:                           ;exit instructions
        mov rax,60
        mov rdx,0
        syscall
        
;*PROCEDURES*       
display:                        ;hex to ascii-hex
        mov rsi,answer+15
        mov rcx,16

loop1:  mov rdx,0
        mov rbx,16
        div rbx
        cmp dl,09h
        jbe skip1
        
        add dl,07h
skip1:  add dl,30h
        mov [rsi],dl
        
        dec rsi
        dec rcx
        jnz loop1
        scall 1,1,answer,16       
ret

stringreverse: 
        mov rsi,string
        mov rdi,string2
        mov rcx,[length]
        add rdi,rcx
        dec rdi
        
loop2:  
        mov al,[rsi]        
        mov [rdi],al
        dec rdi
        inc rsi
        loop loop2

ret