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Little and Big Endian Mystery

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What are these? 
Little and big endian are two ways of storing multibyte data-types ( int, float, etc). In little endian machines, last byte of binary representation of the multibyte data-type is stored first. On the other hand, in big endian machines, first byte of binary representation of the multibyte data-type is stored first. 
Suppose integer is stored as 4 bytes (For those who are using DOS-based compilers such as C++ 3.0, integer is 2 bytes) then a variable x with value 0x01234567 will be stored as following.
 

Little and Big Endian Mystery


 


How to see memory representation of multibyte data types on your machine? 
Here is a sample C code that shows the byte representation of int, float and pointer. 
 

C++

#include <stdio.h>
  
/* function to show bytes in memory, from location start to start+n*/
void show_mem_rep(char *start, int n)
{
    int i;
    for (i = 0; i < n; i++)
         printf(" %.2x", start[i]);
    printf("\n");
}
  
/*Main function to call above function for 0x01234567*/
int main()
{
   int i = 0x01234567;
   show_mem_rep((char *)&i, sizeof(i));
   getchar();
   return 0;
}

                    

C

#include <stdio.h>
  
/* function to show bytes in memory, from location start to start+n*/
void show_mem_rep(char *start, int n)
{
    int i;
    for (i = 0; i < n; i++)
         printf(" %.2x", start[i]);
    printf("\n");
}
  
/*Main function to call above function for 0x01234567*/
int main()
{
   int i = 0x01234567;
   show_mem_rep((char *)&i, sizeof(i));
   getchar();
   return 0;
}

                    

Java

import java.nio.ByteBuffer;
 
public class MemoryRepresentation {
    public static void main(String[] args) {
        // Create an integer value with a hexadecimal representation (0x01234567)
        int i = 0x01234567;
 
        // Convert the integer to its byte representation, reversing the byte order
        byte[] reversedBytes = reverseArray(ByteBuffer.allocate(4).putInt(i).array());
 
        // Display the memory representation of the reversed bytes
        showMemRep(reversedBytes);
    }
 
    // Display the memory representation of a byte array
    public static void showMemRep(byte[] data) {
        for (byte b : data) {
            // Print each byte as a two-digit hexadecimal number
            System.out.printf("%02x ", b & 0xFF);
        }
        System.out.println();
    }
 
    // Reverse the order of bytes in a byte array
    public static byte[] reverseArray(byte[] array) {
        byte[] reversed = new byte[array.length];
        for (int i = 0; i < array.length; i++) {
            // Copy bytes in reverse order to the 'reversed' array
            reversed[i] = array[array.length - 1 - i];
        }
        return reversed;
    }
}

                    

Python3

import ctypes
 
# function to show bytes in memory, from location start to start+n
 
 
def show_mem_rep(start, n):
    # create a ctypes array of unsigned bytes from the buffer
    arr = (ctypes.c_ubyte * n).from_address(ctypes.addressof(start))
    for i in range(n):
        # use hex() to convert integer to hexadecimal string and slice to remove the "0x" prefix
        # use rjust() to right-justify the string with 2 spaces
        print(hex(arr[i])[2:].rjust(2, "0"), end=" ")
    print()
 
 
# Main function to call above function for 0x01234567
if __name__ == "__main__":
    # create a 4-byte integer with value 0x01234567
    i = 0x01234567
    # convert integer i to a byte array in little-endian byte order
    i_bytes_le = i.to_bytes(ctypes.sizeof(ctypes.c_int), byteorder="little")
    # convert integer i to a byte array in big-endian byte order
    i_bytes_be = i.to_bytes(ctypes.sizeof(ctypes.c_int), byteorder="big")
    # create a writable buffer using ctypes.create_string_buffer() and copy the bytes into it
    buf_le = ctypes.create_string_buffer(i_bytes_le)
    buf_be = ctypes.create_string_buffer(i_bytes_be)
    # pass the buffer to show_mem_rep
    print("Little Endian: ", end="")
    show_mem_rep(buf_le, ctypes.sizeof(ctypes.c_int))
    print("Big Endian: ", end="")
    show_mem_rep(buf_be, ctypes.sizeof(ctypes.c_int))

                    

C#

using System;
 
class Program
{
    static void Main(string[] args)
    {
        int i = 0x01234567;
        ShowMemRep(BitConverter.GetBytes(i));
        Console.ReadLine();
    }
 
    static void ShowMemRep(byte[] bytes)
    {
        for (int i = 0; i < bytes.Length; i++)
        {
            Console.Write(" {0:X2}", bytes[i]);
        }
        Console.WriteLine();
    }
}

                    

Javascript

// Function to show bytes in memory, from location start to start+n
function show_mem_rep(start, n) {
    for (let i = 0; i < n; i++) {
        // Print the byte at index i in hexadecimal format with 2 digits
        console.log(` ${start[i].toString(16).padStart(2, '0')}`);
    }
    console.log("\n");
}
 
// Main function to call above function for 0x01234567
function main() {
    // In JavaScript, we don't have specific data types like int or char, so we use numbers
    let i = 0x01234567;
 
    // When accessing memory in JavaScript, we use Typed Arrays
    // Here, we create a Uint8Array view of the memory where `i` is stored
    let byteArray = new Uint8Array(new Uint32Array([i]).buffer);
 
    // Call the show_mem_rep function with the byteArray and its length
    show_mem_rep(byteArray, byteArray.length);
}
 
// Call the main function
main();

                    

Output
 67 45 23 01















Time Complexity: O(1)

Auxiliary Space: O(1)

When above program is run on little endian machine, gives “67 45 23 01” as output, while if it is run on big endian machine, gives “01 23 45 67” as output.
Is there a quick way to determine endianness of your machine? 
There are n no. of ways for determining endianness of your machine. Here is one quick way of doing the same. 
 

C++

#include <bits/stdc++.h>
using namespace std;
int main()
{
    unsigned int i = 1;
    char *c = (char*)&i;
    if (*c)
        cout<<"Little endian";
    else
        cout<<"Big endian";
    return 0;
}
 
// This code is contributed by rathbhupendra

                    

C

#include <stdio.h>
int main()
{
   unsigned int i = 1;
   char *c = (char*)&i;
   if (*c)   
       printf("Little endian");
   else
       printf("Big endian");
   getchar();
   return 0;
}

                    

Java

public class EndiannessCheck {
    public static void main(String[] args) {
        int i = 1; // Initialize an integer with value 1
        byte[] byteArray = toByteArray(i); // Convert integer to byte array
 
        // Check endianness
        if (byteArray[0] == 1) {
            System.out.println("Little endian");
        } else {
            System.out.println("Big endian");
        }
    }
 
    // Utility method to convert an integer to a byte array
    private static byte[] toByteArray(int value) {
        byte[] byteArray = new byte[4];
        for (int i = 0; i < 4; i++) {
            byteArray[i] = (byte) (value >>> (i * 8));
        }
        return byteArray;
    }
}

                    

Python3

import sys
 
def check_endianess():
    i = 1
    c = bytearray(i.to_bytes(4, sys.byteorder))
 
    if c[0]:
        print("Little endian")
    else:
        print("Big endian")
 
# Driver code
check_endianess()

                    

C#

using System;
 
class Program
{
    static void Main(string[] args)
    {
        uint i = 1;
        byte[] bytes = BitConverter.GetBytes(i); // Convert the integer to bytes
 
        if (bytes[0] != 0)
        {
            Console.WriteLine("Little endian");
        }
        else
        {
            Console.WriteLine("Big endian");
        }
    }
}

                    

Javascript

let buffer = new ArrayBuffer(4); // Assuming a 4-byte integer
let view = new DataView(buffer);
 
view.setUint32(0, 1); // Set the value to 1
 
if (view.getUint8(0) === 1) {
    console.log("Little endian");
} else {
    console.log("Big endian");
}

                    

Output
Little endian















Time Complexity: O(1)

Auxiliary Space: O(1)


In the above program, a character pointer c is pointing to an integer i. Since size of character is 1 byte when the character pointer is de-referenced it will contain only first byte of integer. If machine is little endian then *c will be 1 (because last byte is stored first) and if the machine is big endian then *c will be 0. 
Does endianness matter for programmers? 
Most of the times compiler takes care of endianness, however, endianness becomes an issue in following cases.
It matters in network programming: Suppose you write integers to file on a little endian machine and you transfer this file to a big-endian machine. Unless there is little endian to big endian transformation, big endian machine will read the file in reverse order. You can find such a practical example here.
Standard byte order for networks is big endian, also known as network byte order. Before transferring data on network, data is first converted to network byte order (big endian). 
Sometimes it matters when you are using type casting, below program is an example.
 

C++

#include <iostream>
using namespace std;
 
int main() {
unsigned char arr[2] = {0x01, 0x00};
unsigned short int x = *(unsigned short int *) arr;
cout << x << endl;
cin.get();
return 0;
}

                    

c

#include <stdio.h>
int main()
{
    unsigned char arr[2] = {0x01, 0x00};
    unsigned short int x = *(unsigned short int *) arr;
    printf("%d", x);
    getchar();
    return 0;
}

                    

Java

public class Main {
    public static void main(String[] args) {
        byte[] arr = {(byte) 0x01, (byte) 0x00};
        short x = (short)((arr[1] << 8) | (arr[0] & 0xFF));
        System.out.println(x);
    }
}
// This code is contributed by shivhack999

                    

Python

import struct
 
# Declare an array of unsigned char
arr = bytearray([0x01, 0x00])
 
# Interpret the array as an unsigned short int
x = struct.unpack('<H', arr)[0]
 
# Print the result
print(x)

                    

C#

using System;
 
class Program
{
    static void Main()
    {
        // Create a byte array with the same values as the C++ array
        byte[] arr = { 0x01, 0x00 };
 
        // Interpret the byte array as an unsigned short integer
        ushort x = BitConverter.ToUInt16(arr, 0);
 
        // Output the result
        Console.WriteLine(x);
 
        // Wait for user input before exiting (simulating cin.get())
        Console.ReadLine();
    }
}

                    

Javascript

const buffer = new ArrayBuffer(2);
const view = new DataView(buffer);
 
// Set values in little-endian format (assuming little-endian architecture)
view.setUint8(0, 0x01);
view.setUint8(1, 0x00);
 
const x = view.getUint16(0, true); // true indicates little-endian
 
console.log(x);

                    

Output
1















Time Complexity: O(1)

Auxiliary Space: O(1)

In the above program, a char array is typecasted to an unsigned short integer type. When I run above program on little endian machine, I get 1 as output, while if I run it on a big endian machine I get 256. To make programs endianness independent, above programming style should be avoided. 
What are bi-endians? 
Bi-endian processors can run in both modes little and big endian.
What are the examples of little, big endian and bi-endian machines ? 
Intel based processors are little endians. ARM processors were little endians. Current generation ARM processors are bi-endian.
Motorola 68K processors are big endians. PowerPC (by Motorola) and SPARK (by Sun) processors were big endian. Current version of these processors are bi-endians. 
Does endianness affects file formats? 
File formats which have 1 byte as a basic unit are independent of endianness e.g., ASCII files. Other file formats use some fixed endianness format e.g, JPEG files are stored in big endian format. 
Which one is better — little endian or big endian? 
The term little and big endian came from Gulliver’s Travels by Jonathan Swift. Two groups could not agree by which end an egg should be opened -a- the little or the big. Just like the egg issue, there is no technological reason to choose one-byte ordering convention over the other, hence the arguments degenerate into bickering about sociopolitical issues. As long as one of the conventions is selected and adhered to consistently, the choice is arbitrary.
 



Last Updated : 09 Jan, 2024
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