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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:
The two basic types are the arithmetic left shift and the arithmetic right shift. For binary numbers it is a bitwise operation that shifts all of the bits of its operand; every bit in the operand is simply moved a given number of bit positions, and the vacant bit-positions are filled in.
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.
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.
P = 0000 0110 0. Arithmetic right shift. P = 0000 0110 0. The last two bits are 00. P = 0000 0011 0. Arithmetic right shift. P = 0000 0011 0. The last two bits are 10. P = 1101 0011 0. P = P + S. P = 1110 1001 1. Arithmetic right shift. P = 1110 1001 1. The last two bits are 11. P = 1111 0100 1. Arithmetic right shift. The product is 1111 0100 ...
Shift an integer right (shift in sign), return an integer. Base instruction 0x64 shr.un: Shift an integer right (shift in zero), return an integer. Base instruction 0xFE 0x1C sizeof <typeTok> Push the size, in bytes, of a type as an unsigned int32. Object model instruction 0xFE 0x0B starg <uint16 (num)> Store value to the argument numbered num.
The ALU (or arithmetic logic unit) has the following input, output and control lines: 2 32-bit input lines: one for the B bus and one for the bus that is connected directly to the H register. 1 32-bit output line, which is connected directly to the shifter. 6 control lines aimed to select which operation to perform.
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).