content: {-# LANGUAGE CPP #-}
  {-# LANGUAGE MagicHash #-}
  
  -----------------------------------------------------------------------------
  -- |
  -- Module      :  Utils.Containers.Internal.BitUtil
  -- Copyright   :  (c) Clark Gaebel 2012
  --                (c) Johan Tibel 2012
  -- License     :  BSD-style
  -- Maintainer  :  libraries@haskell.org
  -- Portability :  portable
  -----------------------------------------------------------------------------
  --
  -- = WARNING
  --
  -- This module is considered __internal__.
  --
  -- The Package Versioning Policy __does not apply__.
  --
  -- The contents of this module may change __in any way whatsoever__
  -- and __without any warning__ between minor versions of this package.
  --
  -- Authors importing this module are expected to track development
  -- closely.
  
  module GHC.Utils.Containers.Internal.BitUtil
      ( bitcount
      , highestBitMask
      , shiftLL
      , shiftRL
      ) where
  
  import GHC.Prelude.Basic
  import Data.Word
  
  {----------------------------------------------------------------------
    [bitcount] as posted by David F. Place to haskell-cafe on April 11, 2006,
    based on the code on
    http://graphics.stanford.edu/~seander/bithacks.html#CountBitsSetKernighan,
    where the following source is given:
      Published in 1988, the C Programming Language 2nd Ed. (by Brian W.
      Kernighan and Dennis M. Ritchie) mentions this in exercise 2-9. On April
      19, 2006 Don Knuth pointed out to me that this method "was first published
      by Peter Wegner in CACM 3 (1960), 322. (Also discovered independently by
      Derrick Lehmer and published in 1964 in a book edited by Beckenbach.)"
  ----------------------------------------------------------------------}
  
  bitcount :: Int -> Word64 -> Int
  bitcount a x = a + popCount x
  {-# INLINE bitcount #-}
  
  -- The highestBitMask implementation is based on
  -- http://graphics.stanford.edu/~seander/bithacks.html#RoundUpPowerOf2
  -- which has been put in the public domain.
  
  -- | Return a word where only the highest bit is set.
  highestBitMask :: Word64 -> Word64
  highestBitMask w = shiftLL 1 (63 - countLeadingZeros w)
  {-# INLINE highestBitMask #-}
  
  -- Right and left logical shifts.
  shiftRL, shiftLL :: Word64 -> Int -> Word64
  shiftRL = unsafeShiftR
  shiftLL = unsafeShiftL
  