Ones' complement adder/subtractor

Eric Smith eric at brouhaha.com
Sat Oct 2 11:50:31 CDT 2010


  On 10/01/2010 07:16 PM, Chuck Guzis wrote:
 > patent 4,298,952 uses
 > ancillary logic to generate a carry-lookahead signal independent of
 > the adder. I'm not sure if this accomplishes much.

It does exactly what you've asked for.  The point of it is that if 
you're using off-the shelf parts, or off-the-shelf standard cells in an 
ASIC, you already can get adders with the carry lookahead logic.  In an 
FPGA you don't, so the dual-adder design you described (and Sun 
patented) will generally have lower resource utilization and be faster.

Eric




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