Q: How does left shift work?

Left shift (<<) moves all bits to the left by n positions and fills the rightmost positions with zeros. Each left shift by 1 position multiplies the number by 2. For example, 5 << 2 shifts 00000101 to 00010100, which is 5 × 2² = 20. Left shifting is equivalent to multiplying by 2^n where n is the shift amount.

Q: What is the difference between arithmetic and logical right shift?

Arithmetic right shift (>>) preserves the sign bit when shifting, filling the leftmost positions with copies of the sign bit. This maintains the sign for negative numbers. Logical right shift (>>> in some languages) always fills the leftmost positions with zeros, treating the number as unsigned. Arithmetic shift is used for signed integers, logical shift for unsigned.

Question 1

What is a bit shift operation?

Accepted Answer

A bit shift operation moves the bits in a binary number left or right by a specified number of positions. Left shifts multiply the number by powers of 2, while right shifts divide by powers of 2. Bit shifting is a fundamental operation in computer science used for efficient multiplication, division, and bit manipulation.

Question 2

How does left shift work?

Accepted Answer

Left shift (<<) moves all bits to the left by n positions and fills the rightmost positions with zeros. Each left shift by 1 position multiplies the number by 2. For example, 5 << 2 shifts 00000101 to 00010100, which is 5 × 2² = 20. Left shifting is equivalent to multiplying by 2^n where n is the shift amount.

Question 3

What is the difference between arithmetic and logical right shift?

Accepted Answer

Arithmetic right shift (>>) preserves the sign bit when shifting, filling the leftmost positions with copies of the sign bit. This maintains the sign for negative numbers. Logical right shift (>>> in some languages) always fills the leftmost positions with zeros, treating the number as unsigned. Arithmetic shift is used for signed integers, logical shift for unsigned.

Question 4

How do you calculate bit shift manually?

Accepted Answer

To calculate bit shift manually: 1) Convert the number to binary. 2) For left shift, move all bits left by n positions and add n zeros on the right. 3) For right shift, move all bits right by n positions and discard the rightmost bits. 4) For arithmetic right shift, fill left with the sign bit; for logical, fill with zeros. 5) Convert the result back to decimal.

Question 5

What is unsigned right shift?

Accepted Answer

Unsigned right shift (>>>) is a logical right shift that always fills the leftmost positions with zeros, regardless of the sign bit. This effectively treats the number as unsigned. In JavaScript, >>> is the unsigned right shift operator. For positive numbers, >> and >>> produce the same result, but for negative numbers they differ significantly.

Question 6

Why are bit shifts faster than multiplication and division?

Accepted Answer

Bit shift operations are faster because they are single-cycle CPU instructions that directly manipulate bits, while multiplication and division require multiple cycles and more complex circuitry. Left shift by n is equivalent to multiplying by 2^n, and right shift by n is equivalent to dividing by 2^n (integer division). This makes bit shifting useful for performance optimization.

Question 7

What happens to bits that shift out of range?

Accepted Answer

Bits that shift beyond the number's bit width are discarded and lost. In a left shift, the leftmost bits overflow and disappear. In a right shift, the rightmost bits are shifted out. This is important when working with fixed-width integers (8-bit, 16-bit, 32-bit) as overflow can cause unexpected results.

Question 8

How are negative numbers handled in bit shifts?

Accepted Answer

Negative numbers are typically stored in two's complement representation. In arithmetic right shift (>>), the sign bit is preserved by copying it into the new leftmost positions, maintaining the negative value. In unsigned right shift (>>>), zeros are filled regardless of sign, which converts negative numbers to large positive values in the unsigned interpretation.

Question 9

What are common applications of bit shifting?

Accepted Answer

Bit shifting is used in: low-level programming and embedded systems, graphics programming (color manipulation, pixel operations), cryptography and hashing algorithms, network protocols and data compression, optimization (replacing × or ÷ by powers of 2), bit masking and flag operations, and implementing efficient data structures like bit arrays.

Question 10

Can bit shifts cause overflow?

Accepted Answer

Yes, left shifts can cause overflow when bits are shifted beyond the number's maximum bit width. For example, in an 8-bit system, left shifting 255 by any amount causes overflow as the high-order bits are lost. Right shifts don't typically overflow but can lose precision through truncation. Always consider the bit width when performing shift operations.

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