fft.h File Reference

Fast Fourier Transform (FFT) and Inverse FFT (IFFT) interfaces. More...

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Data Structures
struct	fft_plan
struct	fft_multi_plan

Macros
#define	FFT_GENERIC
#define	FFT_SIZE_MIN   1
#define	FFT_SIZE_MAX   1024
#define	FFT_MULTI_COUNT_MAX   3

Functions
struct fft_plan *	mod_fft_plan_new (struct processing_module *mod, void *inb, void *outb, uint32_t size, int bits)
	Allocate and initialize an FFT execution plan.
void	fft_execute_16 (struct fft_plan *plan, bool ifft)
	Execute a 16-bit complex FFT or IFFT according to an initialized plan.
void	fft_execute_32 (struct fft_plan *plan, bool ifft)
	Execute a 32-bit complex FFT or IFFT according to an initialized plan.
void	mod_fft_plan_free (struct processing_module *mod, struct fft_plan *plan)
	Free an allocated FFT execution plan and its internal buffers.
struct fft_multi_plan *	mod_fft_multi_plan_new (struct processing_module *mod, void *inb, void *outb, uint32_t size, int bits)
	mod_fft_multi_plan_new() - Prepare FFT for 2^N size and some other FFT sizes
void	fft_multi_execute_32 (struct fft_multi_plan *plan, bool ifft)
	fft_multi_execute_32() - Calculate Fast Fourier Transform (FFT) for 2^size and other
void	mod_fft_multi_plan_free (struct processing_module *mod, struct fft_multi_plan *plan)
	mod_fft_multi_plan_free() - Free the FFT plan
void	dft3_32 (struct icomplex32 *input, struct icomplex32 *output)
	dft3_32() - Discrete Fourier Transform (DFT) for size 3.

Detailed Description

Fast Fourier Transform (FFT) and Inverse FFT (IFFT) interfaces.

Macro Definition Documentation

FFT_GENERIC

#define FFT_GENERIC

FFT_MULTI_COUNT_MAX

#define FFT_MULTI_COUNT_MAX   3

FFT_SIZE_MAX

#define FFT_SIZE_MAX   1024

FFT_SIZE_MIN

#define FFT_SIZE_MIN   1

Function Documentation

dft3_32()

void dft3_32	(	struct icomplex32 *	input,
		struct icomplex32 *	output
	)

dft3_32() - Discrete Fourier Transform (DFT) for size 3.

Parameters

input	Pointer to complex values input array, Q1.31.
output	Pointer to complex values output array, Q1.31, scaled down by 1/3.

This function is useful for calculating some non power of two FFTs. E.g. the FFT for size 1536 is done with three 512 size FFTs and one 3 size DFT.

fft_execute_16()

void fft_execute_16	(	struct fft_plan *	plan,
		bool	ifft
	)

Execute a 16-bit complex FFT or IFFT according to an initialized plan.

Parameters

plan	Pointer to the initialized 16-bit FFT plan.
ifft	True for Inverse Fast Fourier Transform, false for forward FFT.

fft_execute_32()

void fft_execute_32	(	struct fft_plan *	plan,
		bool	ifft
	)

Execute a 32-bit complex FFT or IFFT according to an initialized plan.

Parameters

plan	Pointer to the initialized 32-bit FFT plan.
ifft	True for Inverse Fast Fourier Transform, false for forward FFT.

fft_multi_execute_32()

void fft_multi_execute_32	(	struct fft_multi_plan *	plan,
		bool	ifft
	)

fft_multi_execute_32() - Calculate Fast Fourier Transform (FFT) for 2^size and other

Parameters

plan	Pointer to FFT plan created with mod_fft_multi_plan_new()
ifft	Value 0 calculates FFT, value 1 calculates IFFT

This function calculates the FFT with the buffers defined with mod_fft_multi_plan_new().

mod_fft_multi_plan_free()

void mod_fft_multi_plan_free	(	struct processing_module *	mod,
		struct fft_multi_plan *	plan
	)

mod_fft_multi_plan_free() - Free the FFT plan

Parameters

mod	Pointer to module
plan	Pointe to FFT plan

This function frees the allocations done internally by the function mod_fft_multi_plan_new(). The input and output buffers need to be freed separately.

mod_fft_multi_plan_new()

struct fft_multi_plan * mod_fft_multi_plan_new	(	struct processing_module *	mod,
		void *	inb,
		void *	outb,
		uint32_t	size,
		int	bits
	)

mod_fft_multi_plan_new() - Prepare FFT for 2^N size and some other FFT sizes

Parameters

mod	Pointer to module
inb	Buffer to use for complex input data
outb	Buffer to use for complex output data
size	Size of FFT as number of bins
bits	World length of FFT. Currently only 32 is supported.

Returns

Pointer to allocated FFT plan

This function does the preparations to calculate FFT. If the size is power of two the operation is similar to mod_fft_plan_new(). Some other FFT sizes like 1536 is supported by allocated multiple FFT plans and by wrapping all needed for similar usage as power of two size FFT.

mod_fft_plan_free()

void mod_fft_plan_free	(	struct processing_module *	mod,
		struct fft_plan *	plan
	)

Free an allocated FFT execution plan and its internal buffers.

Parameters

mod	Processing module that owns the plan.
plan	Pointer to the FFT plan to free.

mod_fft_plan_new()

struct fft_plan * mod_fft_plan_new	(	struct processing_module *	mod,
		void *	inb,
		void *	outb,
		uint32_t	size,
		int	bits
	)

Allocate and initialize an FFT execution plan.

Parameters

mod	Processing module requesting the plan (for memory allocation).
inb	Pointer to input buffer for complex data.
outb	Pointer to output buffer for complex results.
size	FFT transform size in number of complex bins.
bits	Sample word length in bits (16 or 32).

Returns

Pointer to allocated struct fft_plan, or NULL on failure.