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Decimal Floating Point Processor

IP.com Disclosure Number: IPCOM000091205D
Original Publication Date: 1969-Nov-01
Included in the Prior Art Database: 2005-Mar-05
Document File: 1 page(s) / 12K

Publishing Venue

IBM

Related People

Duke, KA: AUTHOR

Abstract

A numerical processor can be built which operates on floating-point numbers where the mantissa is an integer and the characteristic represents a power of 10 by which that integer must be multiplied. Thus, decimal numbers can be represented exactly without conversion errors. Such floating point numbers are expressed as N = (-1)/S/ x 10/X/ x I where S = sign bit, X = exponent, and I = integer.

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Decimal Floating Point Processor

A numerical processor can be built which operates on floating-point numbers where the mantissa is an integer and the characteristic represents a power of 10 by which that integer must be multiplied. Thus, decimal numbers can be represented exactly without conversion errors. Such floating point numbers are expressed as N = (-1)/S/ x 10/X/ x I where S = sign bit, X = exponent, and I = integer.

Both the characteristic and mantissa are expressed in binary form to reduce storage requirements and to simplify arithmetic processes. To add or subtract two numbers, it is necessary to make their characteristic equal. This can be done either by repeatedly multiplying by 10 the integer with the larger characteristic or dividing by 10 the integer with the smaller characteristic or both. The addition or subtraction then becomes a simple binary operation.

Multiplication and division can be executed as pure binary operations with pre- or post-adjustment involving multiplication by appropriate powers of 10. Alternatively, these operations can be performed on a decimal digit-by-digit basis, using any of the algorithms which examine or generate numbers from the least significant end. This implies the presence of a divide-by-ten network which produces a remainder.

The processor can therefore include a binary adder-subtractor for mantissas, a binary adder-subtractor for characteristics, a network for multiplying a mantissa by ten, a network for dividin...