Special.hs

module Numeric.FFT.Special
       ( specialBases
       , specialBaseSizes
       , maxPrimeSpecialBaseSize ) where

import Prelude hiding (filter, maximum)
import Control.Monad.ST
import Data.IntMap.Strict (IntMap)
import qualified Data.IntMap.Strict as IM
import Data.Complex
import Data.Vector.Unboxed
import qualified Data.Vector.Unboxed.Mutable as MV

import Numeric.FFT.Types
import Numeric.FFT.Utils
import Numeric.FFT.Special.Primes
import Numeric.FFT.Special.PowersOfTwo
import Numeric.FFT.Special.Miscellaneous


-- | Map from input vector lengths to hard-coded FFT transforms for
-- small problem sizes.  Each function in the map takes a transform
-- direction (+1 for forward, -1 for inverse) and returns the
-- /unscaled/ transform (scaling for inverse transforms is applied at
-- the top-level).
specialBases :: IntMap (Int -> MVCD s -> MVCD s -> ST s ())
specialBases = IM.fromList [ ( 2, special2)
                           , ( 4, special4)
                           , ( 8, special8)
                           , (16, special16)
                           , (32, special32)
                           , (64, special64)
                           , ( 3, special3)
                           , ( 5, special5)
                           , ( 7, special7)
                           , (11, special11)
                           , (13, special13)
                           , ( 6, special6)
                           , ( 9, special9)
                           , (10, special10)
                           , (12, special12)
                           , (14, special14)
                           , (15, special15)
                           , (20, special20)
                           , (25, special25)
                           ]

-- | Available base transform sizes.
specialBaseSizes :: Vector Int
specialBaseSizes = fromList $ IM.keys specialBases

-- | Largest prime for which we have a specialised base transform.
maxPrimeSpecialBaseSize :: Int
maxPrimeSpecialBaseSize = maximum $ filter isPrime specialBaseSizes