Question 1

What is the difference between logical and arithmetic right shift?

Accepted Answer

Both move bits to the right, but they fill the vacated high bits differently. Logical right shift (>>>) always pads with zeros, so it treats the value as unsigned. Arithmetic right shift (>>) copies the sign bit into the top, so a negative number stays negative. In 8-bit, -8 is the pattern 11111000: logical >> 1 gives 01111100 = 124, while arithmetic >> 1 gives 11111100 = -4. Pick logical for raw unsigned data, arithmetic for signed integers.

Question 2

Why does left shift by 1 multiply by 2?

Accepted Answer

Shifting every bit one place to the left turns the bit worth 1 into worth 2, the bit worth 2 into worth 4, and so on, exactly doubling the value. So 5 << 1 = 10 and 5 << 2 = 20. Each extra position doubles again, which is why n bits of left shift multiplies by 2 to the power n. This holds until a bit reaches the sign position or falls off the top of the chosen width, where overflow changes the result.

Question 3

How does the sign bit behave when I shift?

Accepted Answer

In a fixed width the top bit is the sign: 1 means negative under two's complement. Left shift can push a 1 into that position, flipping a positive number negative (in 8-bit, 64 << 1 = -128). Arithmetic right shift protects the sign by copying it inward, so -8 >> 1 stays negative at -4. Logical right shift ignores the sign entirely and feeds in zeros, which is why it can turn a negative pattern into a large positive number.

Question 4

What happens on bit-width overflow?

Accepted Answer

Each width has a fixed number of bit slots. When a left shift pushes bits past the most significant position, those high bits are simply dropped. In 8-bit, 255 << 1 keeps only the low eight bits = 11111110 = -2, not 510. Choosing 16 or 32 bits gives more room before the same shift overflows. The tool masks the result to your chosen width so what you see matches how a real 8/16/32-bit register would behave.

Question 5

Why does arithmetic right shift act like divide by 2?

Accepted Answer

Dropping the lowest bit halves the value, and floor-rounds toward negative infinity. So 256 >> 2 = 64 and 20 >> 1 = 10. For negatives it still floors: -7 >> 1 = -4, not -3, because floor(-3.5) is -4. That floor behaviour is why >> is not identical to integer division that truncates toward zero. The tool computes the exact floor result inside your chosen width.

Question 6

What does the unsigned right shift >>> do that >> does not?

Accepted Answer

The triple-arrow >>> is the unsigned (logical) right shift. It reads the value purely as a bit pattern, shifts right, and fills the top with zeros no matter what the original sign was. That is its whole job: there is no >>> distinction for positive numbers, but for negatives it diverges sharply. In 32-bit, -1 is 0xFFFFFFFF, and -1 >>> 1 = 0x7FFFFFFF = 2147483647, while -1 >> 1 stays -1. Use >>> when a value is conceptually unsigned bytes, color channels or flags.

Bit Shift Calculator — Left, Logical and Arithmetic Shift

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Bit Shift Calculator — Left, Logical and Arithmetic Shift

Result

What this tool does

Tool details

How to use

1. Input

2. Process

3. Copy / Download

How Bit Shift Calculator fits into your work

Developer jobs

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