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Create An ARM Program To Check If String Is A Palindrome In Assembly Language Assignment Solution.


Instructions

Objective
Write a program to shift string by n bits in Assembly language.

Requirements and Specifications

Objective
For this programming assignment, you will write an ARM program that does the following:
  1. Prints "input a string".
  2. Reads the input string.
  3. Calculates the length of the string.
  4. Outputs the string length to the console.
  5. Determines if the string is a palindrome.
  6. Outputs whether the string is a palindrome
Screenshots of output
program to check if string is a palindrome in Assembly language
program to check if string is a palindrome in Assembly language 1
Source Code
.section .data
input_prompt : .asciz "Input a string: "
input_spec : .asciz "%[^\n]"
length_spec : .asciz "String length: %d\n"
palindrome_spec : .asciz "String is a palindrome (T/F): %c\n"
input: .space 10 // place to save string
.section .text
.global main
# program execution begins here
main:
    ldr x0, =input_prompt // load address of prompt string
    bl printf // print the prompt
    ldr x0, =input_spec // load address of spec to read a string
    ldr x1, =input // load address of place to save string
    bl scanf // read the string
    # calculate length
    ldr x0, =input // load input string address
    mov x19, 0 // start length in zero
loop1:
    ldrb w1, [x0, x19] // load character from string
    cmp w1, 0 // if the character is end of string
    beq endloop1 // terminate loop
    add x19, x19, 1 // else increment string length
    b loop1 // repeat loop
endloop1:
    # print length
    ldr x0, =length_spec // load address of string to print
    mov w1, w19 // copy length to w1
    bl printf // print the length message
    # if length is <= 1, string is palindrome
    cmp x19, 1
    ble palindrome
    # else, check if string is palindrome
    ldr x0, =input // load input string address
    mov w1, 'F' // by defaulf we assume string is not a palindrome
    mov x2, 0 // index from start of string (0)
    sub x3, x19, 1 // index from end of string (length - 1)
loop2:
    ldrb w4, [x0, x2] // load character from start of string
    ldrb w5, [x0, x3] // load character from end of string
    cmp w4, w5 // if the characters are not equal
    bne printtf // print the result, not palindrome
    add x2, x2, 1 // advance start index to next char in string
    add x3, x3, -1 // move end index to previous char in string
    cmp x2, x3 // compare indices
    blt loop2 // continue in loop if indices don't cross
                        // if indices cross, all other chars in front and back
                        // were equal so it's a palindrome
palindrome:
    mov w1, 'T' // is a palindrome
printtf:
    # print palindrome result T or F
    ldr x0, =palindrome_spec // load address of string to print
    bl printf // print the palindrome message
exit:
    mov x0, 0
    mov x8, 93
    svc 0
    ret