libfft (Fast Fourier Transform)

The Fast-Fourier Transform library is a signal processing library for performing FFTs or inverse FFTs efficiently. More...

Files
file	fft.h

Data Structures
struct	COMPLEX

Functions
void	splitdit (int N, int M)
void	ditsplit (int n, int m)
void	rfft (double *X, int N)
	Real valued, split-radix, decimation in time FFT. More...
void	irfft (double *X, int n)
	Split Radix, Decimation in Frequency, Inverse Real-valued FFT. More...
void	cfft (COMPLEX *dat, int num)
	Forward Complex Fourier Transform. More...
void	icfft (COMPLEX *dat, int num)
void	cdiv (COMPLEX *result, COMPLEX *val1, COMPLEX *val2)
void	rfft256 (register double X[])
void	irfft256 (register double X[])

Detailed Description

The Fast-Fourier Transform library is a signal processing library for performing FFTs or inverse FFTs efficiently.

Function Documentation

splitdit()

void splitdit	(	int	N,
		int	M
	)

Generates Real Split Radix Decimation in Time source files

ditsplit()

void ditsplit	(	int	n,
		int	m
	)

Generates Real Split Radix Decimation in Freq Inverse FFT source files

Parameters

n	[in] length
m	[in] n = 2^m

rfft()

void rfft	(	double *	X,
		int	N
	)

Real valued, split-radix, decimation in time FFT.

Data comes out as: [ Re(0), Re(1), ..., Re(N/2), Im(N/2-1), ..., Im(1) ]

irfft()

void irfft	(	double *	X,
		int	n
	)

Split Radix, Decimation in Frequency, Inverse Real-valued FFT.

Input order: [ Re(0), Re(1), ..., Re(N/2), Im(N/2-1), ..., Im(1) ]

Parameters

X	[in] ?
n	[in] length

cfft()

void cfft	(	COMPLEX *	dat,
		int	num
	)

Forward Complex Fourier Transform.

"Fast" Version - Function calls to complex math routines removed. Uses pre-computed sine/cosine tables.

The FFT is:

         N-1
 Xf(k) = Sum x(n)(cos(2PI(nk/N)) - isin(2PI(nk/N)))
         n=0

icfft()

void icfft	(	COMPLEX *	dat,
		int	num
	)

Inverse Complex Fourier Transform

cdiv()

void cdiv	(	COMPLEX *	result,
		COMPLEX *	val1,
		COMPLEX *	val2
	)

Complex divide (why is this public API when none of the other complex math routines are?)

rfft256()

void rfft256

(

register double

X[]

)

irfft256()

void irfft256

(

register double

X[]

)