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Logical right shift differs from arithmetic right shift. Thus, many languages have different operators for them. For example, in Java and JavaScript, the logical right shift operator is >>>, but the arithmetic right shift operator is >>. (Java has only one left shift operator (<<), because left shift via logic and arithmetic have the same effect.)
Arithmetic right shifts are equivalent to logical right shifts for positive signed numbers. Arithmetic right shifts for negative numbers in N's complement (usually two's complement) is roughly equivalent to division by a power of the radix (usually 2), where for odd numbers rounding downwards is applied (not towards 0 as usually expected).
Left arithmetic shift Right arithmetic shift. In an arithmetic shift, the bits that are shifted out of either end are discarded. In a left arithmetic shift, zeros are shifted in on the right; in a right arithmetic shift, the sign bit (the MSB in two's complement) is shifted in on the left, thus preserving the sign of the operand.
When performed on a negative value in a signed type, the result is technically implementation-defined (compiler dependent), [5] however most compilers will perform an arithmetic shift, causing the blank to be filled with the set sign bit of the left operand. Right shift can be used to divide a bit pattern by 2 as shown:
Arithmetic shift: the operand is treated as a two's complement integer, meaning that the most significant bit is a "sign" bit and is preserved. Logical shift: a logic zero is shifted into the operand. This is used to shift unsigned integers.
The very fastest shifters are implemented as full crossbars, in a manner similar to the 4-bit shifter depicted above, only larger. These incur the least delay, with the output always a single gate delay behind the input to be shifted (after allowing the small time needed for the shift count decoder to settle; this penalty, however, is only incurred when the shift count changes).
On arithmetic right shift equivalence to division: It is stated that arithmetic right shift is not equivalent to division by a power of two, but this is only the case if division of negative rounds towards zero; if on a particular machine division rounds towards negative infinity, the right shift is equivalent.
The shifter contains a 32-bit input and output. The output is connected directly to the C bus. The shifter is used to perform logical and arithmetic shift operations, by simply setting respectively the control signal SLL8 (Shift Left Logical) and SRA1 (Shift Right Arithmetic).