/
Adler32.hs
57 lines (48 loc) · 1.7 KB
/
Adler32.hs
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{-# LANGUAGE BangPatterns #-}
{-# LANGUAGE MagicHash #-}
module Codec.Compression.Zlib.Adler32 (
AdlerState,
initialAdlerState,
advanceAdler,
advanceAdlerBlock,
finalizeAdler,
) where
import Data.Bits (shiftL, (.|.))
import qualified Data.ByteString as S
import GHC.Exts (Word#, plusWord#, remWord#)
import GHC.Word (Word32 (..), Word8 (..))
data AdlerState = AdlerState {_adlerA :: Word#, _adlerB :: Word#}
initialAdlerState :: AdlerState
initialAdlerState = AdlerState 1## 0##
advanceAdler :: AdlerState -> Word8 -> AdlerState
advanceAdler (AdlerState a b) (W8# v) = AdlerState a' b'
where
a' = (a `plusWord#` v) `remWord#` 65521##
b' = (b `plusWord#` a') `remWord#` 65521##
{-# INLINE advanceAdler #-}
advanceNoMod :: AdlerState -> Word8 -> AdlerState
advanceNoMod (AdlerState a b) (W8# v) = AdlerState a' b'
where
a' = a `plusWord#` v
b' = b `plusWord#` a'
{-# INLINE advanceNoMod #-}
-- The block must be less than 5552 bytes long in this case
advanceAdlerLimited :: AdlerState -> S.ByteString -> AdlerState
advanceAdlerLimited !state !bl = AdlerState stateA' stateB'
where
!(AdlerState stateA stateB) = S.foldl' advanceNoMod state bl
stateA' = stateA `remWord#` 65521##
stateB' = stateB `remWord#` 65521##
advanceAdlerBlock :: AdlerState -> S.ByteString -> AdlerState
advanceAdlerBlock !state !bl
| S.length bl == 0 = state
| S.length bl == 1 = advanceAdler state (S.head bl)
| S.length bl < 5552 = advanceAdlerLimited state bl
| otherwise = advanceAdlerBlock (advanceAdlerBlock state first5551) rest
where
(!first5551, !rest) = S.splitAt 5551 bl
finalizeAdler :: AdlerState -> Word32
finalizeAdler (AdlerState a b) = high .|. low
where
high = (W32# b) `shiftL` 16
low = W32# a