Bit Operations

Here are concise notes on using bitwise operators in JavaScript — useful for interviews and coding practice:

---

🔹 Basics

JavaScript stores numbers as 64-bit floating point, but bitwise operators work on 32-bit signed integers.

• Signed 32-bit integer → range: -2,147,483,648 to 2,147,483,647

• Bitwise ops truncate numbers to 32-bit, then back to JS Number.

---

🔹 Common Bitwise Operators

Operator	Symbol	Example	Meaning
AND	&	5 & 3 = 1	Bit is 1 only if both bits are 1
OR	|	5 | 3 = 7	Bit is 1 if at least one bit is 1
XOR	^	5 ^ 3 = 6	Bit is 1 if bits differ
NOT	~	~5 = -6	Flips all bits (2’s complement)
Left Shift	<<	5 << 1 = 10	Shift left, fill with 0
Right Shift (Sign-propagating)	>>	5 >> 1 = 2	Shift right, keep sign bit
Unsigned Right Shift	>>>	-5 >>> 1 = 2147483645	Shift right, fill with 0

---

🔹 Useful Tricks

1. Check even/odd

let x = 7;
console.log(x & 1 ? "Odd" : "Even"); // Odd

2. Swap two numbers without temp

let a = 5, b = 9;
a = a ^ b;
b = a ^ b;
a = a ^ b;
console.log(a, b); // 9, 5

3. Multiply or divide by 2

console.log(5 << 1); // 10  (5 * 2)
console.log(20 >> 2); // 5  (20 / 4)

4. Check if k-th bit is set

let n = 13; // 1101
let k = 2;  // (0-indexed from right)
console.log((n & (1 << k)) !== 0); // true (bit is set)

5. Set a bit

n = n | (1 << k);

6. Clear a bit

n = n & ~(1 << k);

7. Toggle a bit

n = n ^ (1 << k);

8. Count set bits (Brian Kernighan’s Algo)

function countBits(n) {
  let count = 0;
  while (n > 0) {
    n = n & (n - 1); // clears the lowest set bit
    count++;
  }
  return count;
}
console.log(countBits(29)); // 4 (11101 has 4 set bits)

🔹 Common Use Cases

• Checking even/odd quickly

• Efficient multiplication/division by powers of 2

• Bit masking (checking flags/permissions)

• Swapping numbers without temp variable

• Subset generation problems

• Low-level optimizations in algorithms

---