{-# LANGUAGE CPP #-}
module Data.Bits.Compat (
popCount,
zeroBits,
finiteBitSize,
countLeadingZeros,
) where
import Data.Bits
#if !MIN_VERSION_base(4,7,0)
#define FiniteBits Bits
#endif
#if !MIN_VERSION_base(4,5,0)
popCount :: Bits a => a -> Int
popCount = go 0
where
go c 0 = c `seq` c
go c w = go (c+1) (w .&. (w - 1))
{-# INLINE popCount #-}
#endif
#if !MIN_VERSION_base(4,7,0)
zeroBits :: Bits a => a
zeroBits = clearBit (bit 0) 0
{-# INLINE zeroBits #-}
finiteBitSize :: Bits a => a -> Int
finiteBitSize = bitSize
{-# INLINE finiteBitSize #-}
#endif
#if !MIN_VERSION_base(4,8,0)
countLeadingZeros :: FiniteBits b => b -> Int
countLeadingZeros x = (w-1) - go (w-1)
where
go i | i < 0 = i
| testBit x i = i
| otherwise = go (i-1)
w = finiteBitSize x
{-# INLINE countLeadingZeros #-}
#endif