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Writing an ARM Program to check if a String is a Palindrome in Assembly Language

In this comprehensive guide, we'll take you step by step through the process of crafting an ARM assembly program dedicated to determining whether a provided string is indeed a palindrome. Our approach involves breaking down the intricate code into easily digestible blocks, accompanied by clear explanations for each block's functionality. By the end of this guide, you'll not only have a solid grasp of palindrome-checking logic in assembly language but also gain valuable insights into ARM programming principles.

Palindrome Detection Using ARM Assembly

Explore our comprehensive guide on how to write an ARM program to determine if a string is a palindrome in assembly language. This step-by-step guide breaks down the code into manageable blocks, providing clear explanations of each block's functionality. Enhance your programming skills and gain insights into palindrome detection while learning how to write your assembly language assignment.


Before you start, it's important to have a basic understanding of ARM assembly language, including its syntax and concepts like registers, memory access, branching, and string manipulation.

The ARM Assembly Program

Below is the ARM assembly code for the palindrome-checking program. We've divided the code into blocks and explained each block's purpose.

```assembly ; Declare the string to be checked .data str: .asciz "madam" ; Main program .text .global main main: @ Initialize registers ldr r0, =str @ Load the address of the string into r0 mov r1, #0 @ Initialize index i = 0 mov r2, #0 @ Initialize index j = 0 loop1: ldrb r3, [r0, r1] @ Load the character at index i into r3 cmp r3, #0 @ Check if the character is null (end of string) beq end_loop1 @ If it is null, exit the loop add r1, r1, #1 @ Increment i b loop1 @ Repeat the loop end_loop1: sub r1, r1, #1 @ Adjust i to point to the last character mov r2, r1 @ Copy i to j for the second loop loop2: ldrb r4, [r0, r2] @ Load the character at index j into r4 ldrb r5, [r0, r1] @ Load the character at index i into r5 cmp r4, r5 @ Compare characters at index i and j bnenot_palindrome @ If they are not equal, the string is not a palindrome cmp r2, r1 @ Compare j and i bgeis_palindrome @ If j >= i, the whole string has been checked add r2, r2, #1 @ Increment j sub r1, r1, #1 @ Decrement i b loop2 @ Repeat the loop not_palindrome: @ Print message for not a palindrome ldr r0, =not_palindrome_msg blprintf bexit_program is_palindrome: @ Print message for palindrome ldr r0, =is_palindrome_msg blprintf exit_program: mov r7, #1 @ Exit syscall swi 0 .data not_palindrome_msg: .asciz "The string is not a palindrome.\n" is_palindrome_msg: .asciz "The string is a palindrome.\n" ```

Explanation of Code Blocks

We'll break down the code into blocks and explain each:

  1.  .data section: The string to be checked is declared here.
  2. .text section: This section contains the main code.
  3. main label: The program's entry point.
  4. Initialize registers: Initial values for used registers are set.
  5. loop1 label: This loop calculates the string's length by counting characters.
  6. 6end_loop1 label: Adjusts i to point to the last character in the string.
  7. loop2 label: This loop compares characters at positions i and j.
  8. not_palindrome label: If characters at positions i and j aren't equal, it's not a palindrome.
  9. is_palindrome label: If the loop completes and all characters match, it's a palindrome.
  10. exit_program label: Exits the program using a system call.
  11. .data section: Contains messages for printing whether the string is a palindrome or not.


This comprehensive guide equips you with a functional ARM assembly program for effectively checking whether a given string is a palindrome. By offering explanations for each code block, you should now possess a solid understanding of ARM assembly principles and the mechanics behind palindrome detection. As you delve deeper into your programming journey, don't hesitate to adapt and experiment with the provided code to further refine your programming skills and problem-solving capabilities.