39 lines
707 B
Factor
39 lines
707 B
Factor
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! Copyright (c) 2007 Hans Schmid.
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! See http://factorcode.org/license.txt for BSD license.
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USING: columns grouping kernel math math.constants math.functions math.vectors
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sequences ;
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IN: math.transforms.fft
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! Fast Fourier Transform
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<PRIVATE
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: n^v ( n v -- w ) [ ^ ] with map ;
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: omega ( n -- n' )
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recip -2 pi i* * * exp ;
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: twiddle ( seq -- seq )
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dup length [ omega ] [ n^v ] bi v* ;
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PRIVATE>
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DEFER: fft
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: two ( seq -- seq )
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fft 2 v/n dup append ;
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<PRIVATE
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: even ( seq -- seq ) 2 group 0 <column> ;
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: odd ( seq -- seq ) 2 group 1 <column> ;
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: (fft) ( seq -- seq )
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[ odd two twiddle ] [ even two ] bi v+ ;
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PRIVATE>
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: fft ( seq -- seq )
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dup length 1 = [ (fft) ] unless ;
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