17 lines
581 B
Factor
17 lines
581 B
Factor
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! Fast Fourier Transform, copyright (C) 2007 Hans Schmid
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! http://dressguardmeister.blogspot.com/2007/01/fft.html
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IN: fft
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USING: arrays sequences math kernel ;
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: n^v ( n v -- w ) [ ^ ] map-with ;
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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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DEFER: fft
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: two ( seq -- seq ) fft 2 v/n dup append ;
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: omega ( n -- n ) recip -2 pi i * * * exp ;
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: twiddle ( seq -- seq ) dup length dup omega swap n^v v* ;
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: (fft) ( seq -- seq ) dup odd two twiddle swap even two v+ ;
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: fft ( seq -- seq ) dup length 1 = [ (fft) ] unless ;
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PROVIDE: demos/fft ;
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