Digital Equipment Corporation

Randy Allmon

Sridhar Samudrala

Sharon Marie Britton

A circuit is provided for using the input operands of a floating point addition or subtraction operation to detect the leading one or zero bit position in parallel with the arithmetic operation. This allows the alignment to be performed on the available result in the next cycle of the floating point operation and results in a significant performance advantage. The leading I/O detection is decoupled from the adder that is computing the result in parallel, eliminating the need for special circuitry to compute a carry-dependent adjustment signal. The single-bit fraction overflow that can result from leading I/O misprediction is corrected with existing circuitry during a later stage of computation.

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Randy Allmon