Logical shift

Logical left shift one bit

In computer science, a logical shift is a shift operator that shifts all the bits of its operand. Unlike an arithmetic shift, a logical shift does not preserve a number's sign bit or distinguish a number's exponent from its mantissa; every bit in the operand is simply moved a given number of bit positions, and the vacant bit-positions are filled in, generally with zeros (compare with a circular shift). A logical shift is often used when its operand is being treated as a sequence of bits rather than as a number. Logical shifts can be useful as efficient ways of performing multiplication or division of unsigned integers by powers of two. Shifting left by n bits on a signed or unsigned binary number has the effect of multiplying it by 2ⁿ. Shifting right by n bits on an unsigned binary number has the effect of dividing it by 2ⁿ (rounding towards 0). Because arithmetic right shift differs from logical right shift, many languages have a different operators for them. For example, in Java and JavaScript, the arithmetic right shift operator is >>; whereas the logical right shift operator is >>>. (Java only has one left shift operator (<<), because arithmetic left shift and logical left shift have the same effect.) C, however, has only one right shift operator, >>. Many C compilers choose which right shift to perform depending on what type of integer is being shifted; often signed integers are shifted using the arithmetic shift, and unsigned integers are shifted using the logical shift.

Example

If the bit sequence 0001 0111 were subjected to a logical shift of one bit position... (please refer images on right side)

• ...to the left would yield: 0010 1110
• ...to the right would yield: 0000 1011