Logical shift
| language | Left | Right |
|---|---|---|
| ARM - assembler | lsl |
lsr
|
| C ++ (unsigned types only) | << |
>>
|
| C (unsigned types only) | << |
>>
|
| Delphi | shl |
shr
|
| Java | << |
>>
|
| Ocaml | lsl |
lsr
|
| Standard ML | << |
>>
|
| Verilog | << |
>>
|
| VHDL | sll |
srl
|
| JavaScript | << |
>>
|
Under a logical shift ( engl. Logical shift ) is understood in the computer science a bitwise operator , all bits shifts the operand. The logical as opposed to the arithmetic shift neither receives the sign bit nor does it distinguish between the exponent and the mantissa of a number. Each bit of the operand is simply shifted by a given number of positions and the resulting bit positions are padded, usually with zeros.
A logical shift is often used when the operand is viewed as a sequence of bits rather than a number.
Logical shifts can be a useful and efficient way to perform multiplications or divisions of unsigned integers (whole numbers) to the power of two. Shifting to the left by n bits for an unsigned or signed binary number has the effect of multiplying by 2 n . Shifting to the right by n bits for an unsigned binary number is equivalent to dividing by 2 n (and then rounding down).
Because arithmetic shifts and logical right shifts are different, many programming languages have different operators for them. So the arithmetic shift operator at is Java and JavaScript , for example >>; whereas the logical right shift >>>is. Java alone has only one left shift operator ( <<) because arithmetic and logical shifting have the same effect.
The language C again only knows one right shift operator >>. Many C compilers decide the type of right shift based on which integer data type should be shifted; Signed integers are often shifted arithmetically and unsigned integers are shifted logically.
example
The following bit sequence should be shifted logically by 1 bit: 0001 0111 (see pictures)
- ... to the left results in: 0010 1110
- ... to the right results in: 0000 1011