Refactor and clean up of math.fft

extra/math/fft/fft.factor

@@ -1,15 +1,38 @@
-! Fast Fourier Transform, copyright (C) 2007 Hans Schmid
-! http://dressguardmeister.blogspot.com/2007/01/fft.html
-USING: arrays sequences math math.vectors math.constants
-math.functions kernel splitting grouping columns ;
+! Copyright (c) 2007 Hans Schmid.
+! See http://factorcode.org/license.txt for BSD license.
+USING: columns grouping kernel math math.constants math.functions math.vectors
+    sequences ;
 IN: math.fft
 
+! Fast Fourier Transform
+
+<PRIVATE
+
 : n^v ( n v -- w ) [ ^ ] with map ;
+
+: omega ( n -- n' )
+    recip -2 pi i* * * exp ;
+
+: twiddle ( seq -- seq )
+    dup length [ omega ] [ n^v ] bi v* ;
+
+PRIVATE>
+
+DEFER: fft
+
+: two ( seq -- seq )
+    fft 2 v/n dup append ;
+
+<PRIVATE
+
 : even ( seq -- seq ) 2 group 0 <column> ;
 : odd ( seq -- seq ) 2 group 1 <column> ;
-DEFER: fft
-: two ( seq -- seq ) fft 2 v/n dup append ;
-: omega ( n -- n' ) recip -2 pi i* * * exp ;
-: twiddle ( seq -- seq ) dup length dup omega swap n^v v* ;
-: (fft) ( seq -- seq ) dup odd two twiddle swap even two v+ ;
-: fft ( seq -- seq ) dup length 1 = [ (fft) ] unless ;
+
+: (fft) ( seq -- seq )
+    [ odd two twiddle ] [ even two ] bi v+ ;
+
+PRIVATE>
+
+: fft ( seq -- seq )
+    dup length 1 = [ (fft) ] unless ;
+