FIR.hs

----------------------------------------------------------------------------
-- |
-- Module      :  ForSyDe.Shallow.FIR
-- Copyright   :  (c) SAM Group, KTH/ICT/ECS 2007-2008
-- License     :  BSD-style (see the file LICENSE)
-- 
-- Maintainer  :  forsyde-dev@ict.kth.se
-- Stability   :  experimental
-- Portability :  portable
--
-- This module implements a FIR filters for the synchronous computational model.
-----------------------------------------------------------------------------
module ForSyDe.Shallow.FIR (firSY) where

import ForSyDe.Shallow.SynchronousLib
import ForSyDe.Shallow.CoreLib

-- | The function firSY implements a FIR-filter for the synchronous computational model. All kinds of FIR-filters can now be modeled by means of 'firSY'. The only argument needed is the list of coefficients, which is given as a vector of any size. To illustrate this, an 8-th order band pass filter is modeled as follows. 
--
-- > bp = firSY (vector [0.06318761339784, 0.08131651217682, 0.09562326700432, 
-- >                     0.10478344432968, 0.10793629404886, 0.10478344432968, 
-- >                     0.09562326700432, 0.08131651217682, 0.06318761339784 ])
-- 
firSY :: Fractional a => Vector a -> Signal a -> Signal a
firSY h = innerProdSY h . sipoSY k 0.0
    where k = lengthV h

sipoSY :: Int -> b -> Signal b -> Vector (Signal b) 
sipoSY n s0 = unzipxSY . scanldSY shiftrV initState
    where initState = copyV n s0

innerProdSY :: (Num a) => Vector a -> Vector (Signal a) -> Signal a
innerProdSY coeffs = zipWithxSY (ipV coeffs)
   where ipV NullV   NullV   = 0
	 ipV (h:>hv) (x:>xv) = h*x + ipV hv xv
         ipV _       _       = error "Vector of different length"