Appeal No. 95-3497
Application 08/158,649
Appellants do not dispute that it was known in the art to
use a shifter to effect division by two. Instead, they argue
(Brief at 4) that (1) the examiner has not pointed to any
suggestion in the Patti references that would have caused one of
ordinary skill in the art to alter the system taught therein so
as to arrive at the present invention, (2) the examiner has
failed to appreciate that "circuitry must be provided at each
sub-operand boundary to assure that the overflow output of the
adding stage at the most significant bit boundary is routed to
the most significant bit of the corresponding partial operand
after the shift," and (3) the Patti references do not teach the
computation of [X ±Y ]/2 and [X ±Y ]/2 in a single instruction.1 1 2 2
We agree with Appellants on the first point and therefore
need not reach the other two. The examiner has not explained,
and it is not apparent to us, why one skilled in the art, knowing
that a shifter can be used to effect division by two, would have
been motivated to use bit shifting in Patti's adder in order to
generate the difference divided by two between the corresponding
8-bit sub-words of the A and B input values. Obviousness cannot
be established by combining the teachings of the prior art to
produce the claimed invention, absent some teaching, suggestion
or incentive supporting the combination." In re Bond, 910 F.2d
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