Signed vs unsigned Shift operators

In JavaScript, >> and >>> are both right-shift operators, but they behave very differently with negative numbers.

1️⃣

>>

—

Arithmetic right shift

👉 Preserves the sign bit

a >> b

• Shifts bits to the right

• Keeps the leftmost (sign) bit

• If number is negative, it fills with 1s

• Works like division by 2 (rounded toward −∞)

Example

5 >> 1
// 5  = 00000000000000000000000000000101
// →  00000000000000000000000000000010
// = 2

-5 >> 1
// -5 = 11111111111111111111111111111011
// →   11111111111111111111111111111101
// = -3

✔ Keeps the number negative

2️⃣

>>>

—

Logical right shift

👉 Does NOT preserve the sign

a >>> b

• Shifts bits to the right

• Always fills with 0****s

• Treats the number as unsigned 32-bit

• Can turn negative numbers into large positives

Example

-5 >>> 1
// -5  = 11111111111111111111111111111011
// →     01111111111111111111111111111101
// = 2147483645

🚨 This is often surprising to people.

3️⃣ Key difference summary

4️⃣ Why

>>

is used in Counting Bits DP

dp[i] = dp[i >> 1] + (i & 1);

• i is non-negative

• i >> 1 safely means divide by 2

• No risk of sign issues

❌ Using >>> here gives no benefit and can confuse readers.

5️⃣ Interview-ready one-liner ✅

>> preserves the sign bit (arithmetic shift), while >>> fills with zeros and treats the number as unsigned.

6️⃣ Rule of thumb

• Use >> for math-like behavior (divide by 2)

• Use >>> when working with raw bit patterns or unsigned values

If you want, I can also explain:

• Why JS bitwise ops are 32-bit signed

• Why 1 << 31 becomes negative

• How this affects LeetCode solutions

Just say 👍