Circuit for rotating, left shifting, or right shifting bits

Abstract

A circuit having a single branch, which is controllable to implement either a left or right shift of bits of a data word. Preferably, the circuit is controllable to implement any selected one of the following operations: a left or right shift of bits of the word; and rotation (to the left or right) of bits of the word. In a preferred implementation, the circuit includes a set of multiplexer stages and circuitry for selectively inverting the order of the bits of the word input to, and the word output from, the set of multiplexer stages. Each of the multiplexer stages shifts the bits of the word it receives either by zero bits (in response to a first control signal), or by a positive number of bits (in response to a second control signal). By selectively controlling various subsets of the multiplexer stages, the bits of the input word can be shifted by any of a number of places (from zero to N, where N is some positive number). In another aspect, the invention is a circuit for rotating bits of an input word (by two or more bits to the left or right) during a single cycle, by duplicating the input word to form an extended word, shifting bits of the extended word, and selecting a subset of the shifted bits of the extended word. Other aspects of the invention are methods performed by, and a digital signal processor including, either embodiment of the inventive circuit.