PFFFT : a Pretty Fast FFT. More...

#include <stddef.h>

Typedefs
typedef struct PFFFT_Setup	PFFFT_Setup

Enumerations
enum	pffft_direction_t { PFFFT_FORWARD , PFFFT_BACKWARD }
	direction of the transform

enum	pffft_transform_t { PFFFT_REAL , PFFFT_COMPLEX }
	type of transform

Functions
PFFFT_Setup *	pffft_new_setup (int N, pffft_transform_t transform)

void	pffft_destroy_setup (PFFFT_Setup *)
	Free the resources used by the fft.

void	pffft_transform (PFFFT_Setup setup, const float input, float output, float work, pffft_direction_t direction)

void	pffft_transform_ordered (PFFFT_Setup setup, const float input, float output, float work, pffft_direction_t direction)

void	pffft_zreorder (PFFFT_Setup setup, const float input, float *output, pffft_direction_t direction)

void	pffft_zconvolve_accumulate (PFFFT_Setup setup, const float dft_a, const float dft_b, float dft_ab, float scaling)

void *	pffft_aligned_malloc (size_t nb_bytes)

void	pffft_aligned_free (void *)
	Free the aligned buffers.

int	pffft_simd_size ()

Detailed Description

PFFFT : a Pretty Fast FFT.

This is basically an adaptation of the single precision fftpack (v4) as found on netlib taking advantage of SIMD instruction found on cpus such as intel x86 (SSE1), powerpc (Altivec), and arm (NEON).

For architectures where no SIMD instruction is available, the code falls back to a scalar version.
Restrictions:

1D transforms only, with 32-bit single precision.
supports only transforms for inputs of length N of the form N=(2^a)*(3^b)*(5^c), a >= 5, b >=0, c >= 0 (32, 48, 64, 96, 128, 144, 160, etc are all acceptable lengths). Performance is best for 128<=N<=8192.
all (float*) pointers in the functions below are expected to have an "simd-compatible" alignment, that is 16 bytes on x86 and powerpc CPUs.

You can allocate such buffers with the functions pffft_aligned_malloc / pffft_aligned_free (or with stuff like posix_memalign..)

Function Documentation

◆ pffft_aligned_malloc()

void * pffft_aligned_malloc ( size_t nb_bytes )

the float buffers must have the correct alignment (16-byte boundary on intel and powerpc). This function may be used to obtain such correctly aligned buffers.

◆ pffft_new_setup()

PFFFT_Setup * pffft_new_setup	(	int	N,
		pffft_transform_t	transform
	)

prepare for performing transforms of size N – the returned PFFFT_Setup structure is read-only so it can safely be shared by multiple concurrent threads.

◆ pffft_simd_size()

int pffft_simd_size ( )

return 4 or 1 wether support SSE/Altivec instructions was enable when building pffft.c

◆ pffft_transform()

void pffft_transform	(	PFFFT_Setup *	setup,
		const float *	input,
		float *	output,
		float *	work,
		pffft_direction_t	direction
	)

Perform a Fourier transform , The z-domain data is stored in the most efficient order for transforming it back, or using it for convolution. If you need to have its content sorted in the "usual" way, that is as an array of interleaved complex numbers, either use pffft_transform_ordered , or call pffft_zreorder after the forward fft, and before the backward fft.

Transforms are not scaled: PFFFT_BACKWARD(PFFFT_FORWARD(x)) = N*x. Typically you will want to scale the backward transform by 1/N.

The 'work' pointer should point to an area of N (2*N for complex fft) floats, properly aligned. If 'work' is NULL, then stack will be used instead (this is probably the best strategy for small FFTs, say for N < 16384).

input and output may alias.

◆ pffft_transform_ordered()

void pffft_transform_ordered	(	PFFFT_Setup *	setup,
		const float *	input,
		float *	output,
		float *	work,
		pffft_direction_t	direction
	)

Similar to pffft_transform, but makes sure that the output is ordered as expected (interleaved complex numbers). This is similar to calling pffft_transform and then pffft_zreorder.

input and output may alias.

◆ pffft_zconvolve_accumulate()

void pffft_zconvolve_accumulate	(	PFFFT_Setup *	setup,
		const float *	dft_a,
		const float *	dft_b,
		float *	dft_ab,
		float	scaling
	)

Perform a multiplication of the frequency components of dft_a and dft_b and accumulate them into dft_ab. The arrays should have been obtained with pffft_transform(.., PFFFT_FORWARD) and should not have been reordered with pffft_zreorder (otherwise just perform the operation yourself as the dft coefs are stored as interleaved complex numbers).

the operation performed is: dft_ab += (dft_a * fdt_b)*scaling

The dft_a, dft_b and dft_ab pointers may alias.

◆ pffft_zreorder()

void pffft_zreorder	(	PFFFT_Setup *	setup,
		const float *	input,
		float *	output,
		pffft_direction_t	direction
	)

call pffft_zreorder(.., PFFFT_FORWARD) after pffft_transform(..., PFFFT_FORWARD) if you want to have the frequency components in the correct "canonical" order, as interleaved complex numbers.

(for real transforms, both 0-frequency and half frequency components, which are real, are assembled in the first entry as F(0)+i*F(n/2+1). Note that the original fftpack did place F(n/2+1) at the end of the arrays).

input and output should not alias.

Typedefs

Enumerations

Functions