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Browse Prior Art Database

64 Bit Adder

IP.com Disclosure Number: IPCOM000076484D
Original Publication Date: 1972-Mar-01
Included in the Prior Art Database: 2005-Feb-24
Document File: 3 page(s) / 139K

Publishing Venue

IBM

Related People

Anderson, RB: AUTHOR

Abstract

The accompanying figures define the logic circuitry used in conjunction with a 64 input bit adder which will add or subtract two 64-bit binary numbers, and normalize the results in a minimum number of logic levels. The adder is designed with zero digit detect logic built in, such that at the same time the sum is formed, a substantial part of the leading zero digit decode is also available.

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64 Bit Adder

The accompanying figures define the logic circuitry used in conjunction with a 64 input bit adder which will add or subtract two 64-bit binary numbers, and normalize the results in a minimum number of logic levels. The adder is designed with zero digit detect logic built in, such that at the same time the sum is formed, a substantial part of the leading zero digit decode is also available.

The basic approach of this circuitry is to provide a 64 input bit adder, which forms the sum, and zero and one, digit and byte detect for the sum, in five levels of the logic. The zero and one detect outputs are available at the same time the sum is generated. This feature is valuable when Post-normalization of the result is required. Post-normalization is the process of shifting the results of the addition such that the most significant "one" bit of the result is in the most significant digit of the final result. To do this, the number of leading zero digits in the sum must be known, in the negative result, the number leading all "one" digits.

The adder in this paper is a wrap-around carry adder with an inhibit wrap- around carry capability and a "force hot one" capability such as the adder shown in IBM Technical Disclosure Bulletin Vol. 14, No. 1, June 1971, p 112-113.

The sum and sum plus one for each four-bit group is decoded by the second and third logic levels. Then in the fifth level, depending on whether or not there is a carry into each of these groups, th...