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|
-- |
-- Module: Math.NumberTheory.Utils.BitMask
-- Copyright: (c) 2020 Andrew Lelechenko
-- Licence: MIT
-- Maintainer: Andrew Lelechenko <andrew.lelechenko@gmail.com>
--
-- Bit mask utilities.
--
{-# LANGUAGE CPP #-}
{-# LANGUAGE MagicHash #-}
module Math.NumberTheory.Utils.BitMask
( indexBitSet
-- , vectorToAddrLiteral
) where
#include "MachDeps.h"
import Data.Bits (countTrailingZeros, finiteBitSize, testBit, (.&.))
import GHC.Exts (Int(..), Word(..), Ptr(..), iShiftRL#, indexWordOffAddr#)
#ifdef WORDS_BIGENDIAN
import GHC.Exts (byteSwap#)
#endif
-- import Data.Bits (unsafeShiftL)
-- import Data.List (unfoldr)
-- import Data.Char (chr)
indexBitSet :: Ptr Word -> Int -> Bool
indexBitSet (Ptr addr#) i@(I# i#) = word `testBit` (i .&. (fbs - 1))
where
fbs = finiteBitSize (0 :: Word)
logFbs# = case countTrailingZeros fbs of
I# l# -> l#
word# = indexWordOffAddr# addr# (i# `iShiftRL#` logFbs#)
#ifdef WORDS_BIGENDIAN
word = W# (byteSwap# word#)
#else
word = W# word#
#endif
-- vectorToAddrLiteral :: [Bool] -> String
-- vectorToAddrLiteral = map (chr . toByte . padTo8) . unfoldr go
-- where
-- go :: [a] -> Maybe ([a], [a])
-- go [] = Nothing
-- go xs = Just (take 8 xs, drop 8 xs)
-- padTo8 :: [Bool] -> [Bool]
-- padTo8 xs
-- | length xs >= 8 = xs
-- | otherwise = xs ++ replicate (8 - length xs) False
-- toByte :: [Bool] -> Int
-- toByte xs = sum $ map (\i -> if xs !! i then 1 `unsafeShiftL` i else 0) [0..7]
|
