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

import Lava
import Xilinx
import Xilinx.OneBitSubtractor

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subtractor :: Xilinx m bit => Int -> (bit, ([bit], [bit])) -> m ([bit], bit)
subtractor n (cin, (a,b)) | length a /= n 
  = error ("subtractor " ++ show n ++ " but length a = " ++ show (length a))
subtractor n (cin, (a,b)) | length b /= n 
  = error ("subtractor " ++ show n ++ " but length b = " ++ show (length b))
subtractor n (cin, (a,b))
  = col n oneBitSubtractor (cin, zip a b)

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subtractor_top :: Int -> Out ()
subtractor_top size
 = do a <- input_vec "a" (size-1) downto 0
      b <- input_vec "b" (size-1) downto 0
      cin <- input_bit "cin"
      (sum, cout) <- subtractor size (cin, (a, b))
      output_vec "sum" sum (size-1) downto 0
      output_bit "cout" cout

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subtractorNoCarryIn :: Xilinx m bit => Int -> ([bit], [bit]) -> m ([bit], bit)
subtractorNoCarryIn n (a, b)
  = subtractor n (one, (a,b))

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