Browse Prior Art Database

IP.com Disclosure Number: IPCOM000048427D
Original Publication Date: 1982-Jan-01
Included in the Prior Art Database: 2005-Feb-08
Document File: 2 page(s) / 51K

IBM

## Related People

Weinberger, A: AUTHOR

## Abstract

A more efficient manner can be used to generate sum bits in a carry look ahead adder. The carry look ahead adder can be described recursively (see article) N(i) equals G(i) plus P(i+1).N(i+1) while the sum is generated as: S(i) equals (P(i) VN(i) plus G(i).P(i+1).N(i+1) where A(i) equals augend bit i B(i) equals addend bit i G(i) equals A(i).B(i) P(i) equals A(i) plus B(i) H(i) equals A(i) VBB(i) S(i) equals sum bit i C(i) equals conventional carry out of bit i N(i) equals new (Ling's) carry out of bit i

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A more efficient manner can be used to generate sum bits in a carry look ahead adder. The carry look ahead adder can be described recursively (see article) N(i) equals G(i) plus P(i+1).N(i+1)

while the sum is generated as:

S(i) equals (P(i) VN(i) plus G(i).P(i+1).N(i+1)

where A(i) equals augend bit i

G(i) equals A(i).B(i)

P(i) equals A(i) plus B(i)

H(i) equals A(i) VBB(i)

S(i) equals sum bit i

C(i) equals conventional carry out of bit i

N(i) equals new (Ling's) carry out of bit i

By relating this new carry N(i) to the conventional carry C(i), a mirror complement new carry M(i) is derived. The conventional carry recursion formula is: (see article).

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