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https://github.com/hajimehoshi/ebiten.git
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69 lines
1.9 KiB
C++
Vendored
69 lines
1.9 KiB
C++
Vendored
/*
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* Copyright 2019 The Android Open Source Project
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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#ifndef RESAMPLER_HYPERBOLIC_COSINE_WINDOW_H
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#define RESAMPLER_HYPERBOLIC_COSINE_WINDOW_H
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#include <math.h>
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namespace resampler {
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/**
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* Calculate a HyperbolicCosineWindow window centered at 0.
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* This can be used in place of a Kaiser window.
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*
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* The code is based on an anonymous contribution by "a concerned citizen":
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* https://dsp.stackexchange.com/questions/37714/kaiser-window-approximation
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*/
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class HyperbolicCosineWindow {
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public:
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HyperbolicCosineWindow() {
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setStopBandAttenuation(60);
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}
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/**
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* @param attenuation typical values range from 30 to 90 dB
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* @return beta
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*/
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double setStopBandAttenuation(double attenuation) {
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double alpha = ((-325.1e-6 * attenuation + 0.1677) * attenuation) - 3.149;
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setAlpha(alpha);
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return alpha;
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}
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void setAlpha(double alpha) {
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mAlpha = alpha;
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mInverseCoshAlpha = 1.0 / cosh(alpha);
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}
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/**
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* @param x ranges from -1.0 to +1.0
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*/
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double operator()(double x) {
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double x2 = x * x;
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if (x2 >= 1.0) return 0.0;
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double w = mAlpha * sqrt(1.0 - x2);
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return cosh(w) * mInverseCoshAlpha;
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}
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private:
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double mAlpha = 0.0;
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double mInverseCoshAlpha = 1.0;
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};
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} // namespace resampler
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#endif //RESAMPLER_HYPERBOLIC_COSINE_WINDOW_H
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