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# Add Subtract Procedures for Use With Recirculating Registers

IP.com Disclosure Number: IPCOM000095640D
Original Publication Date: 1964-Apr-01
Included in the Prior Art Database: 2005-Mar-07
Document File: 2 page(s) / 32K

IBM

## Related People

Bagley, JD: AUTHOR

## Abstract

The recirculating registers alpha and beta, such as either magnetic drum tracks or delay lines, contain numbers A and 13, respectively. There is effected either an addition or subtraction of A to or from 13. The procedures are applicable for numbers A and 13 expressed in any number system. A and 13 are here considered as decimal numbers where each digit is represented by a number of binary bits. It is assumed that A has m digits and 13 has n digits, i.e., A(m), A(m-1), A(m-2), ... A(j), ... A(2), A(1), A(o) B(n), B(n-1), B(n-2), .... B(k), .... B(2), B(1), B(o). where A(m) and B(n) are the most significant digits and A(o) and B(o) are the least significant digits. During successive digit times, A(o) and B(o), A(1) and B(1), etc.

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Add Subtract Procedures for Use With Recirculating Registers

The recirculating registers alpha and beta, such as either magnetic drum tracks or delay lines, contain numbers A and 13, respectively. There is effected either an addition or subtraction of A to or from 13. The procedures are applicable for numbers A and 13 expressed in any number system. A and 13 are here considered as decimal numbers where each digit is represented by a number of binary bits. It is assumed that A has m digits and 13 has n digits, i.e., A(m), A(m-1), A(m-2), ... A(j), ... A(2), A(1), A(o)

B(n), B(n-1), B(n-2), .... B(k), .... B(2), B(1), B(o). where
A(m) and B(n) are the most significant digits and A(o) and B(o) are the least significant digits. During successive digit times, A(o) and B(o), A(1) and B(1), etc., appear at one-digit windows 10 and 12, respectively, of registers alpha and beta.

Add-subtract circuit 14 includes the following three units. The add-one unit adds one to the digit at the reference window. If the digit is a 9, it is changed to a 0 and a carry indication is provided. The subtract-one unit subtracts 1 from the digit at the reference window. If the digit is a 0, it is changed to a 9 and a borrow indication is provided. The count-down unit is similar to the subtract-one unit except there is no provision for a borrow indication. If the digit at the reference window is a 0, the count-down unit does not change it.

The procedure for addition is as follows. For each digi...