;Aim:-
;Write X86/64 ALP for the following operations on the string entered by the user. (use of 64-bit registers is
;expected)
;a) Calculate Length of the string b) Reverse the string
;c) Check whether the string is palindrome
;OR
;Make your program user friendly by providing MENU like:
;(a) Enter the string b) Calculate length of string c) Reverse string d) Check palindrome e) Exit
;Display appropriate messages to prompt the user while accepting the input and displaying the result.

;—————————-declaration of macro———————————
%macro disp 2
mov rax, 1
mov rdi, 1
mov rsi, %1
mov rdx, %2
syscall
%endmacro

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

;———————–data section—————————————
section .data
menu:     db ‘MENU’, 10
db ‘1. Enter the string’, 10
db ‘2. Calculate length of string’, 10
db ‘3. Reverse string’, 10
db ‘4. Check palindrome’, 10
db ‘5. Exit’, 10
db ‘Enter your choice:’, 10
menulen equ $-menu
msg1  db  ‘Enter string:’, 10
msg1len equ $-msg1
msg2 db ‘The length of given string is:’, 10
msg2len equ $-msg2
msg3 db ‘The reverse of the string is:’
msg3len equ $-msg3
msg4 db ‘The given string is palindrome.’, 10
msg4len equ $-msg4
msg5 db ‘The given string is not palindrome.’, 10
msg5len equ $-msg5
msg6 db ‘Thank you for using programme.’, 10
msg6len equ $-msg6
nl db ”, 10, 13
nllen equ $-nl

;————————–bss section————————————
;Notes:-
;Remeber size of strlen and len
section .bss
string: resb 50
choice: resb 2
strlen: resb 8
len: resb 16
rev: resb 50

;——————————–text section————————————–
section .text
global _start
_start:
disp menu, menulen
accept choice, 2

cmp byte[choice], 31h
je get_string
cmp byte[choice], 32h
je length
cmp byte[choice], 33h
je reverse
cmp byte[choice], 34h
je palindrome
cmp byte[choice], 35h
jae exit

get_string:
disp msg1, msg1len
accept string, 50
dec rax
mov [strlen], rax
jmp _start

;—————–logic for length calculation——————————-
;Notes:-
;Get length in bx
;rol bx to get its one digit
;and with 0fh
;Adjust ASCII
;Move it in rdi

length:
mov bx, [strlen]
mov rdi, len
mov rcx, 16
d1:    rol bx, 4
mov dl, bl
and dl, 0fh
cmp dl, 09h
jbe d2
add dl, 07h
d2:    add dl, 30h
mov [rdi], dl
inc rdi
loop d1

disp msg2, msg2len
disp len, 4
disp nl, nllen
jmp _start

;————————-logic for reversing the string—————————–
;Notes:-
;Put one string in rsi
;put the variable of resulting reverse string in rdi
;Add length in rsi
;transfer rsi to rdi decrementing it
reverse:
mov rsi, string
mov rdi, rev
add rsi, [strlen]
mov rcx, [strlen]
a1:    mov al, [rsi]
mov [rdi], al
dec rsi
inc rdi
loop a1

mov al, [rsi]            ;This extra iteration is required for completion of reverse string.
mov [rdi], al

disp msg3, msg3len
disp rev, 50
disp nl, nllen
jmp _start

;—————–logic to check palindrome—————————————
;Notes:-
;put the string in rsi and rdi
;add length in rsi and decrement it once
;compare elements of rsi and rdi
palindrome:            ;************Can be implemented by using string instruction -> repe cmpsb**************
mov rsi, string
mov rdi, string
add rsi, [strlen]
dec rsi                ;This is decremented because go get access of last element
mov rcx, [strlen]
b1:    mov al, [rsi]
cmp [rdi], al
jne b2
dec rsi
inc rdi
loop b1

disp msg4, msg4len
jmp _start
b2:    disp msg5, msg5len
jmp _start

;—————————————exit block————————————–
exit:        disp msg6, msg6len
mov rax, 60
mov rdi, 0
syscall