FIR_transposed.hs

module FIR_transposed where

import CLaSH.Prelude

-- "Normal"
fir1 coeffs us x = (us',y)
  where
    us' = (x +>> us)
    y   = fold (+) (zipWith (*) us coeffs)

-- Transposed
fir2 coeffs us x = (us',y)
  where
    ms  = map (x*) coeffs
    us' = zipWith (+) (us <<+ 0) ms
    y   = head us

-- Transposed v2
fir3 coeffs us x = (us',y)
  where
    ms  = map (x*) coeffs
    us' = zipWith (+) (tail us) (init ms) :< last ms
    y   = head us

t1 :: Signal (Signed 16) -> Signal (Signed 16)
t1 = mealy (fir1 (2:>3:>(-2):>8:>Nil)) (repeat 0)

t2 :: Signal (Signed 16) -> Signal (Signed 16)
t2 = mealy (fir2 (2:>3:>(-2):>8:>Nil)) (repeat 0)

t3 :: Signal (Signed 16) -> Signal (Signed 16)
t3 = mealy (fir3 (2:>3:>(-2):>8:>Nil)) (repeat 0)

testInput :: Signal (Signed 16)
testInput = stimuliGenerator (2:>3:>(-2):>8:>Nil)

-- >>> sampleN 4 (t1 testInput)
-- [0,4,12,1]
-- >>> sampleN 4 (t2 testInput)
-- [0,4,12,1]
-- >>> sampleN 4 (t3 testInput)
-- [0,4,12,1]