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math.transforms.fft: fix Cooley-Tukey only works for powers of two.

db4
John Benediktsson 2014-06-04 12:06:45 -07:00
parent 6bf3470e62
commit e260edc32b
1 changed files with 9 additions and 7 deletions
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16
extra/math/transforms/fft/fft.factor
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@ -6,6 +6,8 @@ IN: math.transforms.fft
<PRIVATE <PRIVATE
DEFER: (fft)
! Discrete Fourier Transform ! Discrete Fourier Transform
:: (slow-fft) ( seq inverse? -- seq' ) :: (slow-fft) ( seq inverse? -- seq' )
seq length :> N seq length :> N
@ -16,7 +18,7 @@ IN: math.transforms.fft
] map ; inline ] map ; inline
! Cooley–Tukey Algorithm ! Cooley–Tukey Algorithm
:: (fft) ( seq inverse? -- seq' ) :: (fast-fft) ( seq inverse? -- seq' )
seq length :> N seq length :> N
N 1 = [ seq ] [ N 1 = [ seq ] [
seq even-indices inverse? (fft) seq even-indices inverse? (fft)
@ -28,19 +30,19 @@ IN: math.transforms.fft
2bi append 2bi append
] if ; inline recursive ] if ; inline recursive
: (fft) ( seq inverse? -- seq' )
over length power-of-2?
[ (fast-fft) ] [ (slow-fft) ] if ; inline recursive
PRIVATE> PRIVATE>
ERROR: not-enough-data ; ERROR: not-enough-data ;
: fft ( seq -- seq' ) : fft ( seq -- seq' )
[ not-enough-data ] [ [ not-enough-data ] [ f (fft) ] if-empty ;
f over length even? [ (fft) ] [ (slow-fft) ] if
] if-empty ;
: ifft ( seq -- seq' ) : ifft ( seq -- seq' )
[ not-enough-data ] [ [ not-enough-data ] [ t (fft) ] if-empty ;
t over length even? [ (fft) ] [ (slow-fft) ] if
] if-empty ;
: correlate ( x y -- z ) : correlate ( x y -- z )
[ fft ] [ reverse fft ] bi* v* ifft ; [ fft ] [ reverse fft ] bi* v* ifft ;