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Data processing apparatus and method for reducing the size of a lookup table

  • US 8,943,118 B2
  • Filed: 07/31/2012
  • Issued: 01/27/2015
  • Est. Priority Date: 07/31/2012
  • Status: Active Grant
First Claim
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1. A data processing apparatus, comprising:

  • processing circuitry configured to perform operations on data; and

    lookup table circuitry configured to receive from the processing circuitry an n-bit input data value, and to return to the processing circuitry an output data value that would be obtained by performance of a predetermined operation on said input data value, the predetermined operation having a first property that the output data value is a function of the input data value, and a second property that a first output data value produced for a first input data value is derivable from a second output data value produced for a second input data value, the lookup table circuitry comprising;

    a lookup table including a plurality of entries, each entry identifying a possible input data value and a corresponding output data value, said plurality of entries being less than 2n;

    input interface circuitry configured to receive the n-bit input data value and to generate an intermediate input data value for provision to the lookup table, the input interface circuitry being configured to detect a modification condition if any of a predetermined number of significant bits of the input data value are logic zero values, the input interface circuitry being configured, if said modification condition is not detected, to retain the input data value as the intermediate input data value, and being configured, if said modification condition is detected, to perform a shift operation on the input data value in order to generate said intermediate input data value;

    output interface circuitry configured to receive from the lookup table an intermediate output data value corresponding to the intermediate input data value generated by the input interface circuitry, and to generate, from the intermediate output data value, the output data value to be returned to the processing circuitry;

    the output interface circuitry being configured, if said modification condition is not detected by the input interface circuitry, to retain the intermediate output data value as said output data value, and being configured, if said modification condition is detected by the input interface circuitry, to perform an output data value derivation operation on the intermediate output data value in order to generate said output data value, the output data value derivation operation at least taking account of the shift operation performed by the input interface circuitry.

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