helper functions

Functions
int	xtract_windowed (const double *data, const int N, const void *argv, double *result)
	Apply a window function to an array of length N. More...
int	xtract_features_from_subframes (const double *data, const int N, const int feature, const void *argv, double *result)
	Divides the array pointed to by *data into two subframes, and applies a given feature to each subframe, returning them in a single array pointed to by result. More...
int	xtract_is_denormal (double const d)
	Test whether a number is denormal.
bool	xtract_is_poweroftwo (unsigned int x)
	Test whether a number is a power of two.
int	xtract_smoothed (const double *data, const int N, const void *argv, double *result)
	Smooth a vector. More...

Detailed Description

Declares helper functions, and their parameters.

Note

These functions don't necessarily conform to the prototype used in xtract_scalar.h and xtract_vector.h etc, and as such are intended to be called 'directly' rather than via the xtract[] function pointer array (libxtract.h)

Function Documentation

int xtract_features_from_subframes	(	const double *	data,
		const int	N,
		const int	feature,
		const void *	argv,
		double *	result
	)

Divides the array pointed to by *data into two subframes, and applies a given feature to each subframe, returning them in a single array pointed to by result.

Parameters

*data	an array of doubles
N	the number of elements in the array pointed by *data
feature	an integer representing the feature to be applied to each subframe in data. This will be a value as given in the enumeration xtract_features_ (libxtract.h)
*argv	a pointer to the argument vector to be passed to the feature extraction function as determined by feature
*result	a pointer to the 'packed' results of the feature calculation. This may be passed in as *data to xtract_features_from_subframes() to calculate further features on the subframes, or xtract_difference_vector(), to get the difference between the subframes.

It is important to ensure that any init*() functions that are called in preparation for functions that are called on subframes are given the subframe size as 'N', and not the frame size. i.e. if xtract_features_from_subframes() is called with N=64, and feature=XTRACT_SPECTRUM, then xtract_init_fft() should be called with N=32.

int xtract_smoothed	(	const double *	data,
		const int	N,
		const void *	argv,
		double *	result
	)

Smooth a vector.

Parameters

*data	a pointer to an array of doubles
N	the number of elements in the array pointed to by *data to be smoothed
*argv	a pointer to a double giving the smoothing gain
*result	a pointer to the first element an array containing the smoothed data

Note

if passing in a spectrum e.g. *result from xtract_spectrum(), then N for xtract_smoothed() should be N / 2 with respect to the N for xtract_spectrum() so only amplitude components are smoothed, not frequencies!

int xtract_windowed	(	const double *	data,
		const int	N,
		const void *	argv,
		double *	result
	)

Apply a window function to an array of length N.

Parameters

*data	a pointer to an array of doubles
N	the number of elements in the array pointed to by *data
*argv	a pointer to a window function as returned by xtract_make_window()
*result	a pointer to the first element an array containing the windowed data

It is up to the caller to generate and free the array containing the window, and to allocate and free memory of size N to hold the data pointed to by *result