dsp::LookupTableTransform< FloatType > Class Template Reference

Class for approximating expensive arithmetic operations. More...

#include <juce_LookupTable.h>

Public Member Functions
	LookupTableTransform ()=default
	Creates an uninitialised LookupTableTransform object.
	LookupTableTransform (const std::function< FloatType(FloatType)> &functionToApproximate, FloatType minInputValueToUse, FloatType maxInputValueToUse, size_t numPoints)
	Creates and initialises a LookupTableTransform object.
void	initialise (const std::function< FloatType(FloatType)> &functionToApproximate, FloatType minInputValueToUse, FloatType maxInputValueToUse, size_t numPoints)
	Initialises or changes the parameters of a LookupTableTransform object.
FloatType	processSampleUnchecked (FloatType value) const noexcept
	Calculates the approximated value for the given input value without range checking.
FloatType	processSample (FloatType value) const noexcept
	Calculates the approximated value for the given input value with range checking.
FloatType	operator[] (FloatType index) const noexcept
FloatType	operator() (FloatType index) const noexcept
void	processUnchecked (const FloatType *input, FloatType *output, size_t numSamples) const noexcept
	Processes an array of input values without range checking.
void	process (const FloatType *input, FloatType *output, size_t numSamples) const noexcept
	Processes an array of input values with range checking.

Static Public Member Functions
static double	calculateMaxRelativeError (const std::function< FloatType(FloatType)> &functionToApproximate, FloatType minInputValue, FloatType maxInputValue, size_t numPoints, size_t numTestPoints=0)
	Calculates the maximum relative error of the approximation for the specified parameter set.

Detailed Description

template<typename FloatType>
class dsp::LookupTableTransform< FloatType >

Class for approximating expensive arithmetic operations.

Once initialised, this class can be used just like the function it approximates via operator().

Example:

LookupTableTransform<float> tanhApprox ([] (float x) { return std::tanh (x); }, -5.0f, 5.0f, 64);
auto outValue = tanhApprox (4.2f);

Note: If you try to call the function with an input outside the provided range, it will return either the first or the last recorded LookupTable value.

See also

LookupTable

Constructor & Destructor Documentation

LookupTableTransform() [1/2]

template<typename FloatType >

dsp::LookupTableTransform< FloatType >::LookupTableTransform ( )

default

Creates an uninitialised LookupTableTransform object.

You need to call initialise() before using the object. Prefer using the non-default constructor instead.

See also

initialise

LookupTableTransform() [2/2]

template<typename FloatType >

dsp::LookupTableTransform< FloatType >::LookupTableTransform	(	const std::function< FloatType(FloatType)> &	functionToApproximate,
		FloatType	minInputValueToUse,
		FloatType	maxInputValueToUse,
		size_t	numPoints )

Creates and initialises a LookupTableTransform object.

Parameters

functionToApproximate	The function to be approximated. This should be a mapping from a FloatType to FloatType.
minInputValueToUse	The lowest input value used. The approximation will fail for values lower than this.
maxInputValueToUse	The highest input value used. The approximation will fail for values higher than this.
numPoints	The number of pre-calculated values stored.

References dsp::LookupTableTransform< FloatType >::initialise().

Member Function Documentation

initialise()

template<typename FloatType >

void dsp::LookupTableTransform< FloatType >::initialise	(	const std::function< FloatType(FloatType)> &	functionToApproximate,
		FloatType	minInputValueToUse,
		FloatType	maxInputValueToUse,
		size_t	numPoints )

Initialises or changes the parameters of a LookupTableTransform object.

Parameters

functionToApproximate	The function to be approximated. This should be a mapping from a FloatType to FloatType.
minInputValueToUse	The lowest input value used. The approximation will fail for values lower than this.
maxInputValueToUse	The highest input value used. The approximation will fail for values higher than this.
numPoints	The number of pre-calculated values stored.

Referenced by dsp::LookupTableTransform< FloatType >::LookupTableTransform().

processSampleUnchecked()

template<typename FloatType >

FloatType dsp::LookupTableTransform< FloatType >::processSampleUnchecked ( FloatType value ) const

noexcept

Calculates the approximated value for the given input value without range checking.

Use this if you can guarantee that the input value is within the range specified in the constructor or initialise(), otherwise use processSample().

Parameters

value

The approximation is calculated for this input value.

Returns

The approximated value for the provided input value.

See also

processSample, operator(), operator[]

References jassert.

Referenced by dsp::LookupTableTransform< FloatType >::operator[](), and dsp::LookupTableTransform< FloatType >::processUnchecked().

processSample()

template<typename FloatType >

FloatType dsp::LookupTableTransform< FloatType >::processSample ( FloatType value ) const

noexcept

Calculates the approximated value for the given input value with range checking.

This can be called with any input values. Out-of-range input values will be clipped to the specified input range.

If the index is guaranteed to be in range use the faster processSampleUnchecked() instead.

Parameters

value

The approximation is calculated for this input value.

Returns

The approximated value for the provided input value.

See also

processSampleUnchecked, operator(), operator[]

References isPositiveAndBelow(), jassert, and jlimit().

Referenced by dsp::LookupTableTransform< FloatType >::operator()(), and dsp::LookupTableTransform< FloatType >::process().

operator[]()

template<typename FloatType >

FloatType dsp::LookupTableTransform< FloatType >::operator[] ( FloatType index ) const

noexcept

See also

processSampleUnchecked

References dsp::LookupTableTransform< FloatType >::processSampleUnchecked().

operator()()

template<typename FloatType >

FloatType dsp::LookupTableTransform< FloatType >::operator() ( FloatType index ) const

noexcept

See also

processSample

References dsp::LookupTableTransform< FloatType >::processSample().

processUnchecked()

template<typename FloatType >

void dsp::LookupTableTransform< FloatType >::processUnchecked ( const FloatType * input, FloatType * output, size_t numSamples ) const

noexcept

Processes an array of input values without range checking.

See also

process

References dsp::LookupTableTransform< FloatType >::processSampleUnchecked().

process()

template<typename FloatType >

void dsp::LookupTableTransform< FloatType >::process ( const FloatType * input, FloatType * output, size_t numSamples ) const

noexcept

Processes an array of input values with range checking.

See also

processUnchecked

References dsp::LookupTableTransform< FloatType >::processSample().

calculateMaxRelativeError()

template<typename FloatType >

static double dsp::LookupTableTransform< FloatType >::calculateMaxRelativeError ( const std::function< FloatType(FloatType)> & functionToApproximate, FloatType minInputValue, FloatType maxInputValue, size_t numPoints, size_t numTestPoints = 0 )

static

Calculates the maximum relative error of the approximation for the specified parameter set.

The closer the returned value is to zero the more accurate the approximation is.

This function compares the approximated output of this class to the function it approximates at a range of points and returns the maximum relative error. This can be used to determine if the approximation is suitable for the given problem. The accuracy of the approximation can generally be improved by increasing numPoints.

Parameters

functionToApproximate	The approximated function. This should be a mapping from a FloatType to FloatType.
minInputValue	The lowest input value used.
maxInputValue	The highest input value used.
numPoints	The number of pre-calculated values stored.
numTestPoints	The number of input values used for error calculation. Higher numbers can increase the accuracy of the error calculation. If it's zero then 100 * numPoints will be used.

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The documentation for this class was generated from the following file:

• juce_LookupTable.h