US 2010/0306291 A1 · Barrel shifter

Abstract

A data processing apparatus is described which comprises processing circuitry responsive to data processing instructions to execute data processing operations and a register file having a set of registers for storing data values for processing by the processing circuitry. The data processing apparatus comprises first shift circuitry which is arranged to receive a data value from the register file and is responsive to a first control signal indicating a first shift amount S1 of between zero and n bit positions to generate a first shifted data value by shifting bit values within the received data value by the first shift amount S1, where n is a predetermined integer. Selection circuitry is provided which is responsive to a second control signal to select between the first shifted data value and a load data value received from a memory. Second shift circuitry is provided which is arranged to receive the data value selected by the selection circuitry and is responsive to a third control signal indicating a second shift amount S2 of a×(n+1) bit positions to generate a second shifted data value by shifting bit values within the received selected data value by the second shift amount S2, where a is zero or an integer. The second shift circuitry is then operable to output the second shifted data value to the register file. In this way, the second shift circuitry of the barrel shifter not only serves to perform byte-level shifting of a data value which has already been partially shifted by the second shift circuitry, but also serves to shift a load data value by an appropriate number of bytes to position it at the least significant byte position (for example) of a register to which the load data value is to be stored. As a result, there is no need to provide a separate load-permute data path to load data values from the memory into the register file.

Claims25

Dependent claims

A data processing apparatus, comprising:

processing circuitry responsive to data processing instructions to execute data processing operations;
a register file having a set of registers for storing data values for processing by the processing circuitry;
first shift circuitry arranged to receive a data value from the register file and responsive to a first control signal indicating a first shift amount S1 of between zero and n bit positions to generate a first shifted data value by shifting bit values within the received data value by the first shift amount S1, where n is a predetermined integer;
selection circuitry responsive to a second control signal to select between the first shifted data value and a load data value received from a memory;
and
second shift circuitry arranged to receive the data value selected by the selection circuitry and responsive to a third control signal indicating a second shift amount S2 of a×(n+1) bit positions to generate a second shifted data value by shifting bit values within the received selected data value by the second shift amount S2, where a is zero or an integer, and to output the second shifted data value to the register file.

3 more elements

Dependencies are inferred from the claim text.

Barrel shifter

Life of this patent

Barrel shifter

Life of this patent

Abstract

Claims25