| 摘要 |
<p>In a modulo p arithmetic apparatus operands are represented as powers of a generator so that multiplications can be performed as simple additions. However, this makes actual addition difficult. Additions are therefore performed by means of a modulo (p-1) subtractor circut (1), a Zech table (2) and a modulo (p-1) adder circuit (3). In order to reduce the size of the Zech table which would otherwise be required, specific values of the output of the subtractor circuit are converted to their negatives modulo (p-1) by means of a converter circuit (15) prior to their application to the Zech table, making use of the fact that each negative modulo (p-1) maps directly to a unique positive number which is often different from the number which was orignally converted. For each number which is converted a multiplexer (18), which normally feeds that input operand (y) which is subtracted in the subtractor circuit to one input (12) of the adder circuit, is switched to feed the other input operand (x) to the adder circuit instead.</p> |
