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-- $Id: OneBitSubtractor.hs#1 2009/10/01 10:31:09 REDMOND\\satnams $
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module Xilinx.OneBitSubtractor
where

import Lava
import Xilinx

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oneBitSubtractor :: Xilinx m bit => (bit, (bit, bit)) -> m (bit, bit)
oneBitSubtractor (cin, (a, b))
  = do part_sum <- nxor2 (a, b)
       sum <- xorcy (part_sum, cin)
       cout <- muxcy (part_sum, (a, cin))
       return (sum, cout)

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oneBitSubtractor_top :: Out ()
oneBitSubtractor_top
 = do a <- input_bit "a"
      b <- input_bit "b"
      cin <- input_bit "cin"
      (sum, cout) <- oneBitSubtractor (cin, (a, b))
      output_bit "sum" sum 
      output_bit "cout" cout 

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