8 {-| This module provides entropy word encoding and decoding functions
9 using a variation on the Rice method. This was introduced in wavpack
10 3.93 because it allows splitting the data into a \"lossy\" stream and
11 a \"correction\" stream in a very efficient manner and is therefore
12 ideal for the "hybrid" mode. For 4.0, the efficiency of this method
13 was significantly improved by moving away from the normal Rice
14 restriction of using powers of two for the modulus divisions and now
15 the method can be used for both hybrid and pure lossless encoding.
17 Samples are divided by median probabilities at 5\/7 (71.43%), 10\/49
18 (20.41%), and 20\/343 (5.83%). Each zone has 3.5 times fewer samples
19 than the previous. Using standard Rice coding on this data would
20 result in 1.4 bits per sample average (not counting sign
21 bit). However, there is a very simple encoding that is over 99%
22 efficient with this data and results in about 1.22 bits per sample. -}
23 module Codec.Audio.WavPack.Words
29 import Codec.Audio.WavPack.Entropy
30 import Codec.Audio.WavPack.Internal
32 import Data.Bitstream.Generic (Bitstream)
33 import qualified Data.Bitstream.Generic as B
35 import qualified Data.Vector.Generic as GV
36 import qualified Data.Vector.Generic.Mutable as MV
37 import Data.Vector.Generic.New (New)
38 import qualified Data.Vector.Generic.New as New
40 import Prelude.Unicode
45 wdBitrateDelta ∷ !(Word32, Word32)
46 , wdBitrateAcc ∷ !(Word32, Word32)
47 , wdPendingData ∷ !Word32
48 , wdHoldingOne ∷ !Word32
49 , wdZeroesAcc ∷ !Word32
50 , wdHoldingZero ∷ !Bool
51 , wdPendingCount ∷ !Int
52 , wdEntropyData ∷ !(EntropyData, EntropyData)
56 -- | This is an optimized version of 'getWord' that is used for
57 -- lossless only ('edErrorLimit' ≡ 0). Also, rather than obtaining a
58 -- single sample, it can be used to obtain an entire buffer of either
59 -- mono or stereo samples.
60 getWordsLossless ∷ ∀bs v. (Bitstream bs, GV.Vector v Int32)
61 ⇒ Bool -- ^ Is the stream monaural?
63 → bs -- ^ WV bitstream.
64 → Int -- ^ Number of samples to get.
65 → (# WordsData, bs, v Int32 #)
66 {-# INLINEABLE getWordsLossless #-}
67 getWordsLossless isMono w0 bs0 nSamples0
68 = let v0 = New.create $ MV.new nSamples
71 v2 = GV.new $ New.take n1 v1
80 go0 ∷ WordsData → bs → Int → New v Int32
81 → (# WordsData, bs, Int, New v Int32 #)
85 | edMedian0 (fst $ wdEntropyData w) < 2 ∧
86 wdHoldingZero w ≡ False ∧
88 edMedian1 (fst $ wdEntropyData w) < 2
89 = if wdZeroesAcc w > 0 then
90 let w' = w { wdZeroesAcc = wdZeroesAcc w - 1 }
92 if wdZeroesAcc w' > 0 then
93 let (# n', v' #) = appendWord 0 n v
99 let cBits = min 33 $ B.length (B.takeWhile id bs)
100 bs' = B.drop cBits bs
105 let (# w', bs'' #) = go0' cBits w bs'
107 if wdZeroesAcc w' > 0 then
110 ( clearMedian $ fst $ wdEntropyData w'
111 , clearMedian $ snd $ wdEntropyData w' )
122 go0' ∷ Word32 → WordsData → bs → (# WordsData, bs #)
125 = let w' = w { wdZeroesAcc = cBits }
129 = let w' = w { wdZeroesAcc = 0 }
133 go0'' ∷ Word32 → Word32 → WordsData → bs → (# WordsData, bs #)
134 go0'' mask cBits w bs
136 = let w' = w { wdZeroesAcc = wdZeroesAcc w .|. mask }
140 = let cBits' = cBits - 1
141 w' = if B.head bs then
142 w { wdZeroesAcc = wdZeroesAcc w .|. mask }
145 mask' = mask `shiftL` 1
148 go0'' mask' cBits' w' bs'
150 go1 ∷ WordsData → bs → Int → New v Int32
151 → (# WordsData, bs, Int, New v Int32 #)
154 = let w' = w { wdHoldingZero = False }
160 go2 ∷ Word32 → WordsData → bs → Int → New v Int32
161 → (# WordsData, bs, Int, New v Int32 #)
163 = let ent = getEntropy n w
165 high = getMedian0 ent
166 ent' = decMedian0 ent
167 w' = setEntropy ent' n w
169 go3 low high w' bs n v
171 = let ent = getEntropy n w
173 high = low + getMedian1 ent - 1
174 ent' = (incMedian0 ∘ decMedian1) ent
175 w' = setEntropy ent' n w
177 go3 low high w' bs n v
179 = let ent = getEntropy n w
180 low = getMedian0 ent + getMedian1 ent
181 high = low + getMedian2 ent - 1
182 ent' = (incMedian0 ∘ incMedian1 ∘ decMedian2) ent
183 w' = setEntropy ent' n w
185 go3 low high w' bs n v
186 go2 onesCount w bs n v
187 = let ent = getEntropy n w
188 low = getMedian0 ent + getMedian1 ent + (onesCount-2) ⋅ getMedian2 ent
189 high = low + getMedian2 ent - 1
190 ent' = (incMedian0 ∘ incMedian1 ∘ incMedian2) ent
191 w' = setEntropy ent' n w
193 go3 low high w' bs n v
195 go3 ∷ Word32 → Word32 → WordsData → bs → Int → New v Int32
196 → (# WordsData, bs, Int, New v Int32 #)
197 go3 low high w bs n v
198 = let (# code, bs' #)
199 = readCode bs (high - low)
201 word = if B.head bs' then
202 fromIntegral $ complement low'
207 = appendWord word n v
211 appendWord ∷ Int32 → Int → New v Int32 → (# Int, New v Int32 #)
213 = let v' = New.modify (\mv → MV.unsafeWrite mv n word) v
218 getEntropy ∷ Int → WordsData → EntropyData
220 | isMono = fst $ wdEntropyData w
221 | n `testBit` 0 = fst $ wdEntropyData w
222 | otherwise = snd $ wdEntropyData w
224 setEntropy ∷ EntropyData → Int → WordsData → WordsData
226 | isMono = w { wdEntropyData = (e, snd $ wdEntropyData w) }
227 | n `testBit` 0 = w { wdEntropyData = (e, snd $ wdEntropyData w) }
228 | otherwise = w { wdEntropyData = (fst $ wdEntropyData w, e) }
230 -- | Read a single unsigned value from the specified bitstream with a
231 -- value from 0 to maxCode. If there are exactly a power of two number
232 -- of possible codes then this will read a fixed number of bits;
233 -- otherwise it reads the minimum number of bits and then determines
234 -- whether another bit is needed to define the code.
235 readCode ∷ Bitstream bs ⇒ bs → Word32 → (# Word32, bs #)
236 {-# INLINEABLE readCode #-}
237 readCode bs 0 = (# 0, bs #)
238 readCode bs 1 = (# b2n (B.head bs), B.tail bs #)
240 = let !bitCount = countBits maxCode
241 !extras = bit bitCount - maxCode - 1
242 !code = B.toBits (B.take (bitCount - 1) bs)
243 (# code', bitCount' #)
244 = if code ≥ extras then
247 + b2n (bs B.!! bitCount)
250 (# code, bitCount - 1 #)
251 !bs' = B.drop bitCount' bs