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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).
In computer programming, a bitwise rotation, also known as a circular shift, is a bitwise operation that shifts all bits of its operand. Unlike an arithmetic shift , a circular shift does not preserve a number's sign bit or distinguish a floating-point number 's exponent from its significand .
CX (Count register): Serves as a counter in loop, string, and shift/rotate instructions. Iterative operations often use CX to determine the number of times a loop or operation should execute. DX (Data register): Used in conjuction with AX for multiplication and division operations that produce results larger than 16 bits.
While what these instructions do is similar to bit level gather-scatter SIMD instructions, PDEP and PEXT instructions (like the rest of the BMI instruction sets) operate on general-purpose registers. [12] The instructions are available in 32-bit and 64-bit versions. An example using arbitrary source and selector in 32-bit mode is:
Below is the full 8086/8088 instruction set of Intel (81 instructions total). [2] These instructions are also available in 32-bit mode, in which they operate on 32-bit registers (eax, ebx, etc.) and values instead of their 16-bit (ax, bx, etc.) counterparts.
Packed shift, with signed shift-amounts. Shift-amount is provided on a per-vector-lane basis, and is taken from the bottom 8 bits of each lane of the last source argument. The shift-amount is considered signed − a positive value will cause left-shift, while a negative value causes right-shift. 8-bit, signed VPSHAB xmm1,xmm2/m128,xmm3: XOP.9 ...
In computing, a linear-feedback shift register (LFSR) is a shift register whose input bit is a linear function of its previous state. The most commonly used linear function of single bits is exclusive-or (XOR). Thus, an LFSR is most often a shift register whose input bit is driven by the XOR of some bits of the overall shift register value.
The formal definition of an arithmetic shift, from Federal Standard 1037C is that it is: . A shift, applied to the representation of a number in a fixed radix numeration system and in a fixed-point representation system, and in which only the characters representing the fixed-point part of the number are moved.