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Fast Determination of Bit Carriers for Binary Adders

IP.com Disclosure Number: IPCOM000061943D
Original Publication Date: 1986-Aug-01
Included in the Prior Art Database: 2005-Mar-09
Document File: 1 page(s) / 11K

Publishing Venue

IBM

Related People

Broker, HJ: AUTHOR

Abstract

A method is described for determining in one level of logic the bit carries in sign-magnitude adders with end-around-carry, to achieve higher performance in a Carry Look Ahead adder. The method is shown in the following sets of equations.

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Fast Determination of Bit Carriers for Binary Adders

A method is described for determining in one level of logic the bit carries in sign-magnitude adders with end-around-carry, to achieve higher performance in a Carry Look Ahead adder. The method is shown in the following sets of equations.

The equations introduce terms that do not depend on the carry out, usually the critical path. Note, for example, the special combinations of propagate and generate terms. These terms can be generated while the carry out is being determined. Carry out does not appear in any expression until the very end of the sets of equations. Thus, an implementation of only one level of logic (an AND/OR level) is needed to combine the value into each bit carry. This method provides improved performance over implementations of a Carry Look Ahead adder with End-Around- Carry.

Disclosed anonymously.

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