Table of Contents

## How is a barrel shifter used with arithmetic instructions?

It is used in conjunction with a processor’s arithmetic logic unit (ALU) or otherwise embedded in the ALU itself. A barrel shifter is able to shift the bits of binary data by moving it from one multiplexer to the next, with the supported number of bits dictated by how many multiplexers are used.

## Which multiplexer will be required for designing a 4-bit barrel shifter?

As there are four control inputs, we need a 16:1 multiplexer for each output bit. Thus for 4 output bits, we need four 16:1 MUX in the design of a 4-bit barrel shifter, in addition we need a 2:1 MUX for fill bit as shown in figure 1.

**Why barrel shifter is used in an ARM processor?**

A barrel shifter is often used to shift and rotate n-bits in modern microprocessors, typically within a single clock cycle. For example, take a four-bit barrel shifter, with inputs A, B, C and D. The shifter can cycle the order of the bits ABCD as DABC, CDAB, or BCDA; in this case, no bits are lost.

### What operations does a barrel shifter perform?

Barrel shifter performs 3 type of shifting operations circular shift, logical shift, arithmetic shift and the amount of shift (typically 1 to n-1 bits). The logical shifter is used to shift the bit in either left or right direction; the empty places are filled by zeros.

### How many multiplexers will be required for designing a 8-bit barrel shifter?

An eight- bit barrel shifter is built out of eight flip-flops and eight 8- to-1 multiplexers; a 8-bit barrel shifter requires 8 registers and thirty-two, 8-to-1 multiplexers, and so on. A schematic representation of an 8-bit barrel shifter is shown in Figure 3.

**What is a logarithmic shifter?**

11 (a), Logarithmic shifter is based on 3:1 MUX cells, consisted of 4 stages with the order of 1-bit, 2-bit, 4-bit and 8-bit shift. It can perform the following operations: shift right logical, shift right arithmetic with sign extension, shift left logical and shift left arithmetic.

## What is a funnel shifter?

As talonmies says, a funnel shifter extracts any contiguous n-bit group of bits from the concatenation of two n-bit words. Note that a funnel shifter provides for efficient implementation of rotates, by making both inputs the same n-bit word.

## What is the difference between shifter and barrel shifter?

The Barrel Shifter is similar to the Shift Register (Multi-bit), except that bits shifted of the register are shifted back into the opposite end of the register. For example, in right shift operations, the LSBs shifted out of the register are shifted into the MSBs.

**What is difference between shift register and barrel shifter?**

### Which instruction category in ARM uses the barrel shifter *?

The ARM arithmetic logic unit has a 32-bit barrel shifter that is capable of shift and rotate operations. The second operand to many ARM and Thumb data-processing and single register data-transfer instructions can be shifted, before the data-processing or data-transfer is executed, as part of the instruction.