cannam@95: (*
cannam@95:  * Copyright (c) 1997-1999 Massachusetts Institute of Technology
cannam@95:  * Copyright (c) 2003, 2007-11 Matteo Frigo
cannam@95:  * Copyright (c) 2003, 2007-11 Massachusetts Institute of Technology
cannam@95:  *
cannam@95:  * This program is free software; you can redistribute it and/or modify
cannam@95:  * it under the terms of the GNU General Public License as published by
cannam@95:  * the Free Software Foundation; either version 2 of the License, or
cannam@95:  * (at your option) any later version.
cannam@95:  *
cannam@95:  * This program is distributed in the hope that it will be useful,
cannam@95:  * but WITHOUT ANY WARRANTY; without even the implied warranty of
cannam@95:  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
cannam@95:  * GNU General Public License for more details.
cannam@95:  *
cannam@95:  * You should have received a copy of the GNU General Public License
cannam@95:  * along with this program; if not, write to the Free Software
cannam@95:  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  USA
cannam@95:  *
cannam@95:  *)
cannam@95: 
cannam@95: (* 
cannam@95:  * The LittleSimplifier module implements a subset of the simplifications
cannam@95:  * of the AlgSimp module.  These simplifications can be executed
cannam@95:  * quickly here, while they would take a long time using the heavy
cannam@95:  * machinery of AlgSimp.  
cannam@95:  * 
cannam@95:  * For example, 0 * x is simplified to 0 tout court by the LittleSimplifier.
cannam@95:  * On the other hand, AlgSimp would first simplify x, generating lots
cannam@95:  * of common subexpressions, storing them in a table etc, just to
cannam@95:  * discard all the work later.  Similarly, the LittleSimplifier
cannam@95:  * reduces the constant FFT in Rader's algorithm to a constant sequence.
cannam@95:  *)
cannam@95: 
cannam@95: open Expr
cannam@95: 
cannam@95: let rec makeNum = function
cannam@95:   | n -> Num n
cannam@95: 
cannam@95: and makeUminus = function
cannam@95:   | Uminus a -> a 
cannam@95:   | Num a -> makeNum (Number.negate a)
cannam@95:   | a -> Uminus a
cannam@95: 
cannam@95: and makeTimes = function
cannam@95:   | (Num a, Num b) -> makeNum (Number.mul a b)
cannam@95:   | (Num a, Times (Num b, c)) -> makeTimes (makeNum (Number.mul a b), c)
cannam@95:   | (Num a, b) when Number.is_zero a -> makeNum (Number.zero)
cannam@95:   | (Num a, b) when Number.is_one a -> b
cannam@95:   | (Num a, b) when Number.is_mone a -> makeUminus b
cannam@95:   | (Num a, Uminus b) -> Times (makeUminus (Num a), b)
cannam@95:   | (a, (Num b as b')) -> makeTimes (b', a)
cannam@95:   | (a, b) -> Times (a, b)
cannam@95: 
cannam@95: and makePlus l = 
cannam@95:   let rec reduceSum x = match x with
cannam@95:     [] -> []
cannam@95:   | [Num a] -> if Number.is_zero a then [] else x
cannam@95:   | (Num a) :: (Num b) :: c -> 
cannam@95:       reduceSum ((makeNum (Number.add a b)) :: c)
cannam@95:   | ((Num _) as a') :: b :: c -> b :: reduceSum (a' :: c)
cannam@95:   | a :: s -> a :: reduceSum s
cannam@95: 
cannam@95:   in match reduceSum l with
cannam@95:     [] -> makeNum (Number.zero)
cannam@95:   | [a] -> a 
cannam@95:   | [a; b] when a == b -> makeTimes (Num Number.two, a)
cannam@95:   | [Times (Num a, b); Times (Num c, d)] when b == d ->
cannam@95:       makeTimes (makePlus [Num a; Num c], b)
cannam@95:   | a -> Plus a
cannam@95: