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In computer science, a logical shift is a bitwise operation that shifts all the bits of its operand. The two base variants are the logical left shift and the logical right shift . This is further modulated by the number of bit positions a given value shall be shifted, such as shift left by 1 or shift right by n .
However, logical operators treat each operand as having only one value, either true or false, rather than treating each bit of an operand as an independent value. Logical operators consider zero false and any nonzero value true. Another difference is that logical operators perform short-circuit evaluation.
Java adds the operator ">>>" to perform logical right shifts, but since the logical and arithmetic left-shift operations are identical for signed integer, there is no "<<<" operator in Java. More details of Java shift operators: [10] The operators << (left shift), >> (signed right shift), and >>> (unsigned right shift) are called the shift ...
In all single-bit shift operations, the bit shifted out of the operand appears on carry-out; the value of the bit shifted into the operand depends on the type of shift. 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.
MIPS I has instructions to perform left and right logical shifts and right arithmetic shifts. The operand is obtained from a GPR (rt), and the result is written to another GPR (rd). The shift distance is obtained from either a GPR (rs) or a 5-bit "shift amount" (the "sa" field).
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).
Shift registers don't need many pins or address decoding logic, so was much cheaper than random-access memory back then. [2] Such shift register memory was sometimes called circulating memory . Datapoint 3300 , for example, stored its terminal display of 25 rows of 72 columns of 6-bit upper-case characters using 54 200-bit shift registers ...
To determine if a number is a power of two, conceptually we may repeatedly do integer divide by two until the number won't divide by 2 evenly; if the only factor left is 1, the original number was a power of 2. Using bit and logical operators, there is a simple expression which will return true (1) or false (0):