module Codec.Binary.Gray.Bits
( gray
, binary
, showBits
) where
import Data.Bits
( Bits, testBit, setBit, clearBit, bitSize
, shiftL, shiftR, complement, xor, (.&.), (.|.), isSigned)
import qualified Codec.Binary.Gray.List as L
shiftR' :: (Bits a) => a -> Int -> a
shiftR' n 0 = n
shiftR' n s
| isSigned n && signum n == 1 =
let n' = clearBit (shiftR n 1) (bitSize n 1)
in shiftR' n' (s1)
| otherwise = shiftR n s
gray :: (Bits a) => a -> a
gray n = n `xor` (shiftR' n 1)
binary :: (Bits a) => a -> a
binary 0 = 0
binary n =
binary' mask0 n (copyMSB n)
where
sz = bitSize n 1
mask0 = let m = setBit 0 sz in (m, m)
copyMSB n = (setBit 0 sz) .&. n
binary' (maskReady, maskLast) ngray nbin
| complement maskReady == 0 = nbin
| otherwise =
let
sz = bitSize ngray 1
nReady = maskReady .&. nbin
maskReady' = setBit (shiftR maskReady 1) sz
maskLast' = shiftR' maskLast 1
nNext = (shiftR' (maskLast .&. nReady) 1) `xor` (maskLast' .&. ngray)
in
binary' (maskReady', maskLast') ngray (nReady .|. nNext)
showBits :: (Bits a) => a -> String
showBits = L.showBits . L.toList