High performance adder for multiple parallel add operations

Details High performance adder for multiple parallel add operations High performance adder for multiple parallel add operations

1998-01-23

1999-12-14

Donaghue, Larry D.

Electrical computers and digital processing systems: processing

Instruction decoding

Decoding instruction to accommodate variable length...

712 42, 708518, 708709, G06F 742, G06F 744

Patent

active

060031255

ABSTRACT:
An adder unit for a microprocessor, being capable, in response to a first control signal, of adding two full word data values, stored in a first storage location and in a second storage location, respectively, and being capable, in response to a second control signal, of adding in parallel four half word data values, a first half word data value and a second half word data value being stored in the first storage location at the low half and the high half thereof, respectively, and a third half word data value and a fourth half word data value being stored in the second storage location at the low half and the high half thereof, respectively. The adder unit includes a first half word adder, arranged so as to add the first half word and the third half word to provide a first sum output of the adder unit, and a first carry out signal. The adder unit also includes a second half word adder arranged so as to add the second half word and the fourth half word, with a carry-in of 0 to provide a second sum output. The adder unit also includes a third half word adder arranged so as to add the second half word and the fourth half word, with a carry-in of 1 to provide a third sum output. Finally, the adder unit includes logic responsive to the first and the second control signals such that when the first control signal is present and the first carry-out signal is a 0, the logic provides the second sum output as a second sum output of the adder, to be concatenated with the first sum output of the adder, but, when the first control signal is present and the first carry-out signal is a 1, the logic provides the third sum output as a second sum output of the adder, to be concatonated with the first sum output of the adder. On the othe hand, when the second control signal is present, the logic provides the second sum output as a second sum output of the adder.

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