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 v' = New.modify (\mv → MV.unsafeWrite mv n 0) v
100 let cBits = min 33 $ B.length (B.takeWhile id bs)
101 bs' = B.drop cBits bs
106 let (# w', bs'' #) = go0' cBits w bs'
108 if wdZeroesAcc w' > 0 then
111 ( clearMedian $ fst $ wdEntropyData w'
112 , clearMedian $ snd $ wdEntropyData w' )
114 v' = New.modify (\mv → MV.unsafeWrite mv n 0) v
123 go0' ∷ Word32 → WordsData → bs → (# WordsData, bs #)
126 = let w' = w { wdZeroesAcc = cBits }
130 = let w' = w { wdZeroesAcc = 0 }
134 go0'' ∷ Word32 → Word32 → WordsData → bs → (# WordsData, bs #)
135 go0'' mask cBits w bs
137 = let w' = w { wdZeroesAcc = wdZeroesAcc w .|. mask }
141 = let cBits' = cBits - 1
142 w' = if B.head bs then
143 w { wdZeroesAcc = wdZeroesAcc w .|. mask }
146 mask' = mask `shiftL` 1
149 go0'' mask' cBits' w' bs'
151 go1 ∷ WordsData → bs → Int → New v Int32
152 → (# WordsData, bs, Int, New v Int32 #)
155 = let w' = w { wdHoldingZero = False }
161 go2 ∷ Word32 → WordsData → bs → Int → New v Int32
162 → (# WordsData, bs, Int, New v Int32 #)
164 = let ent = getEntropy n w
166 high = getMedian0 ent
167 ent' = decMedian0 ent
168 w' = setEntropy ent' n w
170 go3 low high w' bs n v
172 = let ent = getEntropy n w
174 high = low + getMedian1 ent - 1
175 ent' = (incMedian0 ∘ decMedian1) ent
176 w' = setEntropy ent' n w
178 go3 low high w' bs n v
180 = let ent = getEntropy n w
181 low = getMedian0 ent + getMedian1 ent
182 high = low + getMedian2 ent - 1
183 ent' = (incMedian0 ∘ incMedian1 ∘ decMedian2) ent
184 w' = setEntropy ent' n w
186 go3 low high w' bs n v
187 go2 onesCount w bs n v
188 = let ent = getEntropy n w
189 low = getMedian0 ent + getMedian1 ent + (onesCount-2) ⋅ getMedian2 ent
190 high = low + getMedian2 ent - 1
191 ent' = (incMedian0 ∘ incMedian1 ∘ incMedian2) ent
192 w' = setEntropy ent' n w
194 go3 low high w' bs n v
196 go3 ∷ Word32 → Word32 → WordsData → bs → Int → New v Int32
197 → (# WordsData, bs, Int, New v Int32 #)
198 go3 low high w bs n v
199 = let (# code, bs' #)
200 = readCode bs (high - low)
202 a = if B.head bs' then
203 fromIntegral $ complement low'
207 v' = New.modify (\mv → MV.unsafeWrite mv n a) v
212 getEntropy ∷ Int → WordsData → EntropyData
214 | isMono = fst $ wdEntropyData w
215 | n `testBit` 0 = fst $ wdEntropyData w
216 | otherwise = snd $ wdEntropyData w
218 setEntropy ∷ EntropyData → Int → WordsData → WordsData
220 | isMono = w { wdEntropyData = (e, snd $ wdEntropyData w) }
221 | n `testBit` 0 = w { wdEntropyData = (e, snd $ wdEntropyData w) }
222 | otherwise = w { wdEntropyData = (fst $ wdEntropyData w, e) }
224 -- | Read a single unsigned value from the specified bitstream with a
225 -- value from 0 to maxCode. If there are exactly a power of two number
226 -- of possible codes then this will read a fixed number of bits;
227 -- otherwise it reads the minimum number of bits and then determines
228 -- whether another bit is needed to define the code.
229 readCode ∷ Bitstream bs ⇒ bs → Word32 → (# Word32, bs #)
230 {-# INLINEABLE readCode #-}
231 readCode bs 0 = (# 0, bs #)
232 readCode bs 1 = (# b2n (B.head bs), B.tail bs #)
234 = let !bitCount = countBits maxCode
235 !extras = bit bitCount - maxCode - 1
236 !code = B.toBits (B.take (bitCount - 1) bs)
237 (# code', bitCount' #)
238 = if code ≥ extras then
241 + b2n (bs B.!! bitCount)
244 (# code, bitCount - 1 #)
245 !bs' = B.drop bitCount' bs