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/*
Copyright 2018 Google Inc. All Rights Reserved.
Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at
http://www.apache.org/licenses/LICENSE-2.0
Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS-IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
*/
#ifndef RESONANCE_AUDIO_AMBISONICS_ASSOCIATED_LEGENDRE_POLYNOMIALS_GENERATOR_H_
#define RESONANCE_AUDIO_AMBISONICS_ASSOCIATED_LEGENDRE_POLYNOMIALS_GENERATOR_H_
#include <stddef.h>
#include <vector>
namespace vraudio {
// Generates associated Legendre polynomials.
class AssociatedLegendrePolynomialsGenerator {
public:
// Constructs a generator for associated Legendre polynomials (ALP).
//
// @param max_degree The maximum ALP degree supported by this generator.
// @param condon_shortley_phase Whether the Condon-Shortley phase, (-1)^order,
// should be included in the polynomials generated.
// @param compute_negative_order Whether this generator should compute
// negative-ordered polynomials.
AssociatedLegendrePolynomialsGenerator(int max_degree,
bool condon_shortley_phase,
bool compute_negative_order);
// Generates the associated Legendre polynomials for the given |x|, returning
// the computed sequence.
//
// @param x The abscissa (the polynomials' variable).
// @return Output vector of computed values.
std::vector<float> Generate(float x) const;
// Gets the number of associated Legendre polynomials this generator produces.
//
// @return The number of associated Legendre polynomials this generator
// produces.
size_t GetNumValues() const;
// Gets the index into the output vector for the given |degree| and |order|.
//
// @param degree The polynomial's degree.
// @param order The polynomial's order.
// @return The index into the vector of computed values corresponding to the
// specified ALP.
size_t GetIndex(int degree, int order) const;
private:
// Computes the ALP for (degree, order) the given |x| using recurrence
// relations. It is assumed that the ALPs necessary for each computation are
// already computed and stored in |values|.
//
// @param degree The degree of the polynomial being computed.
// @param degree The order of the polynomial being computed.
// @param values The previously computed values.
// @return The computed polynomial.
inline float ComputeValue(int degree, int order, float x,
const std::vector<float>& values) const;
// Checks the validity of the given index.
//
// @param degree The polynomial's degree.
// @param order The polynomial's order.
inline void CheckIndexValidity(int degree, int order) const;
// The maximum polynomial degree that can be computed; must be >= 0.
int max_degree_ = 0;
// Whether the Condon-Shortley phase, (-1)^order, should be included in the
// polynomials generated.
bool condon_shortley_phase_ = false;
// Whether this generator should compute negative-ordered polynomials.
bool compute_negative_order_ = false;
};
} // namespace vraudio
#endif // RESONANCE_AUDIO_AMBISONICS_ASSOCIATED_LEGENDRE_POLYNOMIALS_GENERATOR_H_
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