Access Control Systems using Bitwise Operators

Application of using Bitwise Operators in JS

Access Control System

Bitwise operators are powerful tools for managing binary data. One practical use case is in implementing an access control system. Let's break down how this can be done step-by-step.

Access Control System Using Bitwise Operators

In this example, we will use bitwise operators to manage permissions for read, write, and execute operations.

Step 1: Define Permission Constants

First, define constants for each type of permission using their decimal equivalents:

const readPermission = 4;    // Binary: 100
const writePermission = 2;   // Binary: 010
const executePermission = 1; // Binary: 001

Step 2: Initialize Permissions

Initialize a variable to store the permissions. Initially, it is set to 0, meaning no permissions:

let myPermission = 0;

Step 3: Add Permissions Using Bitwise OR (`|`)

Use the bitwise OR operator to add permissions. The bitwise OR operator allows us to combine multiple permissions:

myPermission = myPermission | readPermission | writePermission;
console.log(myPermission); // Output: 6

Explanation:

readPermission is 4 (binary 100)
writePermission is 2 (binary 010)
4 | 2 results in 6 (binary 110), meaning both read and write permissions are granted.

Step 4: Check Permissions Using Bitwise AND (`&`)

To check if a specific permission is granted, use the bitwise AND operator:

let message = (myPermission & readPermission) ? 'yes' : 'no';
console.log(message); // Output: yes

Explanation:

myPermission & readPermission checks if the readPermission bit is set in myPermission.
If the result is not 0, it means the permission is granted.

Step 5: Remove a Permission and Check Again

To demonstrate how removing a permission affects the check:

myPermission = myPermission & ~readPermission;
message = (myPermission & readPermission) ? 'yes' : 'no';
console.log(message); // Output: no

Explanation:

~readPermission inverts the bits of readPermission, making it 011.
myPermission & ~readPermission clears the readPermission bit in myPermission.

Practical Example

Here is the complete code from the lecture, along with the explanations:

const readPermission = 4;    // Binary: 100
const writePermission = 2;   // Binary: 010
const executePermission = 1; // Binary: 001

let myPermission = 0;
myPermission = myPermission | readPermission | writePermission;
console.log(myPermission); // Output: 6 (Binary: 110)

let message = (myPermission & readPermission) ? 'yes' : 'no';
console.log(message); // Output: yes

// Remove readPermission and check again
myPermission = myPermission & ~readPermission;
message = (myPermission & readPermission) ? 'yes' : 'no';
console.log(message); // Output: no

Summary of Bitwise Operators in Access Control

Bitwise OR (|): Used to add permissions.
Bitwise AND (&): Used to check if a specific permission is granted.
Bitwise NOT (~): Used to invert bits, helpful for clearing specific permissions.

Key Takeaways

Permissions as Flags: Each bit in a binary number represents a different permission (flag). By combining these flags, you can manage multiple permissions efficiently.
Bitwise OR: Combines multiple flags.
Bitwise AND: Checks if a specific flag is set.
Bitwise NOT: Inverts bits, useful for clearing flags.

Understanding these concepts allows for efficient and powerful manipulation of binary data, which is useful in many real-world applications beyond access control systems.

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