Hewlett-packard Development Company, L.P.

Digital Equipment Corporation

John D Clouser

Gilbert M Wolrich

Mark D Matson

William R Grundmann

Sridhar Samudrala

The shifters () that a floating-point processor ()'s addition pipeline () uses to align or normalize floating-point operands' mantissas before addition or subtraction shift a given mantissa pair one more bit to the left for subtraction than for addition. As a result, the addition pipeline's rounding circuitry () does not need to be capable of adding round bits in as many positions as it would without the shift difference, so it can be simpler and faster. Similarly, circuitry (and) employed for normalization after addition and subtraction can be simpler because it does not have to implement as shift options.

Reduction of add-pipe logic by operand offset shift

In a digital processor performing division, quotient accumulation apparatus is formed of a set of muxes and a single carry save adder. Partial quotients are accumulated in carry-save form with proper sign extension. Delay of partial quotient bit fragments from one iteration to a following iteration enables the apparatus to limit use to one carry save adder. By enlarging minimal logic, the quotient accumulation apparatus operates at a rate fast enough to support the rate of fast dividers.

Method and apparatus for accumulating partial quotients in a digital processor

If the exponents of a floating-point-processor addition pipeline's input operands are equal, a signal (INVERT) that determines whether the pipeline's sole full-width carry-propagate mantissa adder (34) will invert one of its inputs results from an inversion-determination circuit (FIG. 11) that determines whether the sole set bit in a decoded normalization-shift signal (NORM.sub.-- SHIFT) occupies the same position as a set bit in a signal (FRAC.sub.-- A.sub.-- GT.sub.-- B) representing what the possible normalization amounts will be if a first of the mantissas is greater than the other, second mantissa. Consequently, a bit-comparison operation (56) that employs no full-width carry-propagate addition can determine the amount of normalization shifting to be performed by bit shifters (30 and 32) disposed in respective processing trains that generate mantissa inputs to the mantissa adder (34).

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Pepperell, MA, United States of America

John D Clouser