Marvell International Limited

Marvell Asia Pte., Ltd.

Ranjan B Lokappa

Igor Arsovski

An adder includes a primary carry bit generation circuit and a summing circuit. The primary carry bit generation circuit is configured to generate first carry bits for a first number of pairs of bits from first and second operands, and to generate second carry bits for a second number of pairs of bits from the first and second operands. The second number of pairs being different than the first number of pairs. The summing circuit is configured to generate first sums by adding bits of pairs from the first and second number of pairs and the first and second carry bits. The summing circuit is configured to generate second sums by adding bits of other pairs of the bits from first and second operands than the pairs in the first and second number of pairs and additional carry bits generated when adding the bits of the other pairs.

Parallel-prefix adder and method

Disclosed is a parallel prefix adder structure with a carry bit generation circuit that generates primary carry bits for only some bit pairs and a sum circuit with ripple carry adders that use these primary carry bits to generate secondary carry bits and sum bits for a final sum. The carry bit generation circuit has different sections, which process different sequential sets of bit pairs and which have different sparsity configurations. As a result, generation of the primary carry bits is non-uniform. That is, in the different sections the primary carry bits are generated at different carry bit-to-bit pair ratios (e.g., the carry bit-to-bit pair ratios for the different sections can be 1:2, 1:4, and 1:2, respectively). For optimal performance, the specific bit pairs for which these primary carry bits are generated varies depending upon whether the maximum operand size is an odd number of bits or an even number.

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Winooski, VT, United States of America

Ranjan B Lokappa