Browse Prior Art Database

Adder

IP.com Disclosure Number: IPCOM000076658D
Original Publication Date: 1972-Apr-01
Included in the Prior Art Database: 2005-Feb-24
Document File: 2 page(s) / 53K

Publishing Venue

IBM

Related People

Singh, S: AUTHOR

Abstract

This is a fast adder for adding more than three numbers, the digits of each of which are arranged in groups in accordance with the expression n = (log(2) (k-1)) where: (log(2) (k-1)) is the smallest integer greater or equal to log(2) (k-1) n = the number of digits in each group and k = the number of numbers to be added.

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Adder

This is a fast adder for adding more than three numbers, the digits of each of which are arranged in groups in accordance with the expression n = (log(2) (k-1)) where: (log(2) (k-1)) is the smallest integer greater or equal to log(2) (k-1) n = the number of digits in each group and k = the number of numbers to be added.

In an adder for adding input numbers (Fig. 1) the most significant digit of each group of three digits are applied to adders 3, 4, 29 and 30 (the number of adders being equal to the number of the groups), each of which directly produces a partial sum consisting of a sum digit and carry digits. In the next cycle of operation, the second most significant digits of each group of digits are applied to the same adders to produce corresponding partial sums in the same manner. Then, the third most significant digits of each group of digits are applied to the same adders. Each partial sum includes a number of digits having overlapping positional significance (weight) with respect to an equal number of digits of another partial sum. However, no more than two digits possess the same positional significance. Half of the digits from all of the partial sums are applied to a first register 26 and the remainder of the digits are applied to a second register 27 with appropriate positional significance. One additional cycle is required in order to apply the digits in the two registers to a carry look-ahead adder 31, to yield the desired final sum.

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