Matsushita Electric Industrial Co., Ltd.

Panasonic Corporation

Daisuke Takeuchi

Kazufumi Tanoue

Tomoko Chiba

When a barrel shift device is divided into pipeline registers and a shift process is executed in a multistage process stage, by decoding a second control signal for controlling a shift amount of a second shift circuitusing a decoding circuitit is detected at what digit positions in intermediate data in an intermediate data holding circuitdata elements which are to be finally output as output data from the second shift circuitare located. Based on a result of the detection of digit positions by the decoding circuitthe intermediate data holding circuitholds only data elements to be finally output, among data elements in the intermediate data, and does not hold unnecessary data elements which are not included in the output data. Therefore, by controlling a data storage operation in the intermediate data holding circuitan increase in power due to the pipeline structure is suppressed.

Barrel shift device

In order to correct an overflow of a multiplication result while improving the operation speed, an overflow detection unit detects an overflow based on whether a multiplicand A and a multiplier B are both a negative value with the largest absolute value. A carry-save adder adds together in carry-save addition partial products and &#x2212;1 (where all bits are 1) as a first correction value to output an intermediate sum and an intermediate carry corresponding to A&#xd7;B&#x2212;1. A carry-propagate adder adds together in carry-propagate addition the intermediate sum, the intermediate carry and a second correction value to output the multiplication result. Where there is no overflow, the second correction value becomes 1 to cancel out the first correction value, whereby the operation result is A&#xd7;B. Where there is an overflow, the second correction value becomes 0, whereby the operation result is A&#xd7;B&#x2212;1 in which the overflow is corrected by the first correction value.

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Osaka, Japan

Daisuke Takeuchi