{-# LANGUAGE FlexibleInstances     #-}
{-# LANGUAGE MultiParamTypeClasses #-}
{-# LANGUAGE ScopedTypeVariables   #-}
{-# LANGUAGE TypeFamilies          #-}

module HaskellWorks.Data.Bits.Broadword.Word8
  ( h
  , l
  , kBitDiff
  , kBitDiffPos
  , kBitDiffUnsafe
  ) where

import Data.Word
import HaskellWorks.Data.Bits.BitWise

-- | Initialise all sub-words of size k where 'k' ∈ { 2, 4, 8, 16, 32 } such that the lowest bit is set to 1 and all other bits are cleared.
--
-- >>> import Numeric(showHex)
-- >>> showHex (l 2) ""
-- "55"
-- >>> showHex (l 4) ""
-- "11"
-- >>> showHex (l 8) ""
-- "1"
l :: Int -> Word8
l :: Int -> Word8
l Int
2 = Word8
0x55
l Int
4 = Word8
0x11
l Int
8 = Word8
0x01
l Int
k = [Char] -> Word8
forall a. HasCallStack => [Char] -> a
error ([Char]
"Invalid h k where k = " [Char] -> [Char] -> [Char]
forall a. [a] -> [a] -> [a]
++ Int -> [Char]
forall a. Show a => a -> [Char]
show Int
k)
{-# INLINE l #-}

-- | Initialise all sub-words of size k where 'k' ∈ { 2, 4, 8, 16, 32 } such that the highest bit is set to 1 and all other bits are cleared.
--
-- >>> import Numeric(showHex)
-- >>> showHex (h 2) ""
-- "aa"
-- >>> showHex (h 4) ""
-- "88"
-- >>> showHex (h 8) ""
-- "80"
h :: Int -> Word8
h :: Int -> Word8
h Int
2 = Word8
0xaa
h Int
4 = Word8
0x88
h Int
8 = Word8
0x80
h Int
k = [Char] -> Word8
forall a. HasCallStack => [Char] -> a
error ([Char]
"Invalid h k where k = " [Char] -> [Char] -> [Char]
forall a. [a] -> [a] -> [a]
++ Int -> [Char]
forall a. Show a => a -> [Char]
show Int
k)
{-# INLINE h #-}

-- | Broadword subtraction of sub-words of size 'k' where 'k' ∈ { 2, 4, 8 }.
--
-- The subtraction respects 2's complement so sub-words may be regarded as signed or unsigned words.
--
-- >>> import Numeric(showHex)
-- >>> showHex (kBitDiff 8 0x02 0x01) ""
-- "1"
-- >>> showHex (kBitDiff 8 0x01 0x02) ""
-- "ff"
-- >>> showHex (kBitDiff 8 0xff 0xff) ""
-- "0"
kBitDiff :: Int -> Word8 -> Word8 -> Word8
kBitDiff :: Int -> Word8 -> Word8 -> Word8
kBitDiff Int
k Word8
x Word8
y = ((Word8
x Word8 -> Word8 -> Word8
forall a. BitWise a => a -> a -> a
.|. Int -> Word8
h Int
k) Word8 -> Word8 -> Word8
forall a. Num a => a -> a -> a
- (Word8
y Word8 -> Word8 -> Word8
forall a. BitWise a => a -> a -> a
.&. Word8 -> Word8
forall a. BitWise a => a -> a
comp (Int -> Word8
h Int
k))) Word8 -> Word8 -> Word8
forall a. BitWise a => a -> a -> a
.^. ((Word8
x Word8 -> Word8 -> Word8
forall a. BitWise a => a -> a -> a
.^. Word8 -> Word8
forall a. BitWise a => a -> a
comp Word8
y) Word8 -> Word8 -> Word8
forall a. BitWise a => a -> a -> a
.&. Int -> Word8
h Int
k)
{-# INLINE kBitDiff #-}

-- | Broadword subtraction of sub-words of size 'k' where 'k' ∈ { 2, 4, 8 } where results are bounded from below by 0.
--
-- >>> import Numeric(showHex)
-- >>> showHex (kBitDiff 8 0x02 0x01) ""
-- "1"
-- >>> showHex (kBitDiff 8 0x01 0x02) ""
-- "ff"
-- >>> showHex (kBitDiff 8 0xff 0xff) ""
-- "0"
kBitDiffPos :: Int -> Word8 -> Word8 -> Word8
kBitDiffPos :: Int -> Word8 -> Word8 -> Word8
kBitDiffPos Int
k Word8
x Word8
y =
                                                                        -- let !_ = trace (">> x = " <> bitShow x) x in
                                                                        -- let !_ = trace (">> y = " <> bitShow y) y in
  let d :: Word8
d = Int -> Word8 -> Word8 -> Word8
kBitDiff Int
k Word8
x Word8
y                                            in  -- let !_ = trace (">> d = " <> bitShow d) d in
  let s :: Word8
s = Int -> Word8 -> Word8 -> Word8
kBitDiff Int
k Word8
0 ((Word8 -> Word8
forall a. BitWise a => a -> a
comp Word8
d Word8 -> Word8 -> Word8
forall a. BitWise a => a -> a -> a
.&. Int -> Word8
h Int
k) Word8 -> Count -> Word8
forall a. Shift a => a -> Count -> a
.>. Int -> Count
forall a b. (Integral a, Num b) => a -> b
fromIntegral (Int
k Int -> Int -> Int
forall a. Num a => a -> a -> a
- Int
1))  in  -- let !_ = trace (">> s = " <> bitShow s) s in
  let r :: Word8
r = Word8
d Word8 -> Word8 -> Word8
forall a. BitWise a => a -> a -> a
.&. Word8
s                                                   in  -- let !_ = trace (">> r = " <> bitShow r) r in
  Word8
r
{-# INLINE kBitDiffPos #-}

-- | Broadword subtraction of sub-words of size 'k' where 'k' ∈ { 2, 4, 8 } where all the sub-words of 'x' and 'y' must
-- not have the signed bit set for the result to be meaningful.
--
-- >>> import Numeric(showHex)
-- >>> showHex (kBitDiffUnsafe 8 0x02 0x01) ""
-- "1"
-- >>> showHex (kBitDiffUnsafe 8 0x01 0x02) ""
-- "ff"
-- >>> showHex (kBitDiffUnsafe 8 0xff 0xff) "" -- produces nonsense in the last sub-word
-- "80"
kBitDiffUnsafe :: Int -> Word8 -> Word8 -> Word8
kBitDiffUnsafe :: Int -> Word8 -> Word8 -> Word8
kBitDiffUnsafe Int
k Word8
x Word8
y = ((Word8
x Word8 -> Word8 -> Word8
forall a. BitWise a => a -> a -> a
.|. Int -> Word8
h Int
k) Word8 -> Word8 -> Word8
forall a. Num a => a -> a -> a
- Word8
y) Word8 -> Word8 -> Word8
forall a. BitWise a => a -> a -> a
.^. Int -> Word8
h Int
k
{-# INLINE kBitDiffUnsafe #-}