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# Efficient Add/Sub/Cmp Algorithm for IEEE Floating Point Operands

IP.com Disclosure Number: IPCOM000035063D
Original Publication Date: 1989-May-01
Included in the Prior Art Database: 2005-Jan-28
Document File: 2 page(s) / 37K

IBM

## Related People

Brown, JD: AUTHOR [+2]

## Abstract

An algorithm and a hardware implementation of the algorithm that performs IEEE floating point addition and subtraction is constructed here. When taking the difference between two numbers, the algorithm selects between ones and twos complement arithmetic to guarantee a signed magnitude answer will always be generated. This selection removes the need for twos complementing the result and improves the performance of the algorithm. The figure is a block diagram illustrating the fraction dataflow for the hardware implementation of this process. The ALIGNER selects the operand fraction with the smaller exponent. The ALIGNER then shifts the fraction the correct number of bits to the right. The output of the aligner is passed to the "right" input of the ADDER.

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Efficient Add/Sub/Cmp Algorithm for IEEE Floating Point Operands

An algorithm and a hardware implementation of the algorithm that performs IEEE floating point addition and subtraction is constructed here. When taking the difference between two numbers, the algorithm selects between ones and twos complement arithmetic to guarantee a signed magnitude answer will always be generated. This selection removes the need for twos complementing the result and improves the performance of the algorithm. The figure is a block diagram illustrating the fraction dataflow for the hardware implementation of this process. The ALIGNER selects the operand fraction with the smaller exponent. The ALIGNER then shifts the fraction the correct number of bits to the right. The output of the aligner is passed to the "right" input of the ADDER. The "left" input to the ADDER is the unaligned fraction of the other operand. The type of arithmetic performed by the ADDER on the two fractions is selected to provide a signed magnitude answer in one clock cycle. This is accomplished by using either ones complement arithmetic, twos complement arithmetic or signed magnitude arithmetic. The ones and twos complement arithmetic are used when the difference between two operands is needed. The signed magnitude arithmetic is used when the sum of two operands is needed. It is this combined use of the three types of arithmetic that makes this algorithm faster. If the sum of the two fractions is needed (additi...