Re: [Haskell-cafe] Request for optimizing help.
First, why do you think your code is non-optimal?
you don't show your main program, so we don't know what you're measuring.
Just by looking at some types (and not analysing the algorithm):
11 data FilterState a = FilterState {
14 , taps :: [a] -- current delay tap stored values
the State really is taps only. (as and bs don't change ?)
so taps should be separate.
25 newTaps = wk : init (taps s)
init could be expensive (linear in the list length)
(but you have linear cost elsewhere, so maybe it does not hurt)
Use some different sequence type (instead of list)?
It seems you actually want a strict sequence (while (:) is lazy)
of strict values.
31 runFilter :: Kernel a - FilterState a - [a] - IO ([a], FilterState a)
why IO? there's no IO in the implementation. it looks like a simple fold.
the type is polymorphic, so ghc needs to be able
to inline the dictionary arguments. (I think that it means that
it wants to see all the code when compiling main, but I'm not sure.
Experts can tell by studing -ddump-simpl output.)
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[Haskell-cafe] Request for optimizing help.
Does anyone have any advice for optimizing the code, below?
Currently, the profiling results look like this:
COST CENTREMODULE %time %alloc
runFilter Filter90.9 41.0
convT Filter 9.1 58.6
Thanks for any help!
-db
11 data FilterState a = FilterState {
12 as :: [a] -- transfer function denominator coefficients
13 , bs :: [a] -- transfer function numerator coefficients
14 , taps :: [a] -- current delay tap stored values
15 } deriving (Show)
16
17 type Kernel a = (a, FilterState a) - (a, FilterState a)
18
19 -- FILTER KERNELS
20 -- Time domain convolution filter (FIR or IIR),
21 -- expressed in direct form 2
22 convT :: (Fractional a) = Kernel a
23 convT (x, s) =
24 let wk = (x - sum [a * t | (a, t) - zip (tail $ as s) (taps s)]) /
head (as s)
25 newTaps = wk : init (taps s)
26 s' = s {taps = newTaps}
27 y = sum [b * w | (b, w) - zip (bs s) (wk : taps s)]
28 in (y, s')
29
30 -- FILTER APPLICATION
31 runFilter :: Kernel a - FilterState a - [a] - IO ([a], FilterState a)
32 runFilter f s0 [] = do
33 return ([], s0)
34 runFilter f s0 (x:xs) = do
35 (y, s') - return (f (x, s0))
36 (ys, s) - runFilter f s' xs
37 return (y:ys, s)
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