A barrel shifter is a digital circuit that can shift a data word by any number of bits in a single cycle. It is implemented as a sequence of multiplexors: the output of one MUX is connected to the input of the next MUX in a way that depends on the shift distance. The number of multiplexors required is log₂(n), where n is the computer's register size. Shift may refer to Look up shift in Wiktionary, the free dictionary. ... In computing, word is a term for the natural unit of data used by a particular computer design. ... BIT is an acronym for: Bangalore Institute of Technology Bilateral Investment Treaty Bhilai Institute of Technology - Durg Birla Institute of Technology - Mesra Battles in Time (Doctor Who magazine) Category: ... The term multiplexer has uses in several fields of application: Electronics In electronics, a multiplexer or mux is a device that combines several electrical signals into a single signal. ...

Take for example a four-bit barrel shifter, with inputs A, B, C and D. The shifter can cyclically alter the order of the bits ABCD. That is, it can 'shift' all of the outputs up to three positions to the right (and thus make any cyclic combination of A, B, C and D). The barrel shifter has a variety of applications, including being a vital component in microprocessors (alongside the ALU). Microprocessors, including an Intel 80486DX2 and an Intel 80386. ... ALU redirects here. ...

The barrel shifter is used in floating-point arithmetic hardware. For a floating-point add or subtract operation, the fractions of the numbers must be aligned, which requires shifting the smaller number (in magnitude) to the right, increasing its exponent, until it matches the exponent of the larger number. This is done by subtracting the exponents, and using the barrel shifter to shift the smaller number to the right by the difference, in one cycle. If a simple shifter were used, shifting by n bit positions would require n clock cycles.

External links

• Google Answers has a good explanation, and collection of links
• University of Hamburg for a useful Java Barrel shifter.

References

This article was originally based on material from the Free On-line Dictionary of Computing, which is licensed under the GFDL. The Free On-line Dictionary of Computing (FOLDOC) is an on-line, searchable encyclopedic dictionary of computing subjects. ... GNU logo (similar in appearance to a gnu) The GNU Free Documentation License (GNU FDL or simply GFDL) is a copyleft license for free content, designed by the Free Software Foundation (FSF) for the GNU project. ...