new function: countBits

diff --git a/Codec/Audio/WavPack/Internal.hs b/Codec/Audio/WavPack/Internal.hs
index bb4cd3713e6ee8fabc82cf90a875032f9b22494d..5769a3fac37f202ab813a0f4074d467b3e6610d6 100644 (file)
--- a/Codec/Audio/WavPack/Internal.hs
+++ b/Codec/Audio/WavPack/Internal.hs
@@ -12,6 +12,8 @@ module Codec.Audio.WavPack.Internal
 
     , exp2s
     , exp2
+
+    , countBits
     )
     where
 import Data.Int
@@ -35,7 +37,7 @@ packWeight !w
         fromIntegral w'''
 
 -- | Convert a packed weight to internal weight (+/-1024). Note that
--- the following equation might not hold because 'packWeight' is
+-- the following equation /might not hold/ because 'packWeight' is
 -- lossy.
 --
 -- > unpackWeight . packWeight = id
@@ -123,6 +125,15 @@ exp2 !l
         else
             exp2l `shiftL` fromIntegral (l' - 9)
 
+-- | 'countBits' @av@ returns the number of bits that is required to
+-- represent @av@.
+countBits ∷ Word32 → Word8
+countBits av
+    | av < (1 `shiftL`  8) = getNBits (fromIntegral  av)
+    | av < (1 `shiftL` 16) = getNBits (fromIntegral (av `shiftR`  8)) +  8
+    | av < (1 `shiftL` 24) = getNBits (fromIntegral (av `shiftR` 16)) + 16
+    | otherwise            = getNBits (fromIntegral (av `shiftR` 24)) + 24
+
 getNBits ∷ Word8 → Word8
 getNBits = UV.unsafeIndex nbitsTable ∘ fromIntegral
     where