Move dead submodules in-tree

Signed-off-by: swurl <swurl@swurl.xyz>

externals/oboe/src/flowgraph/resampler/HyperbolicCosineWindow.h

@@ -0,0 +1,71 @@
+/*
+ * Copyright 2019 The Android Open Source Project
+ *
+ * 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 RESAMPLER_HYPERBOLIC_COSINE_WINDOW_H
+#define RESAMPLER_HYPERBOLIC_COSINE_WINDOW_H
+
+#include <math.h>
+
+#include "ResamplerDefinitions.h"
+
+namespace RESAMPLER_OUTER_NAMESPACE::resampler {
+
+/**
+ * Calculate a HyperbolicCosineWindow window centered at 0.
+ * This can be used in place of a Kaiser window.
+ *
+ * The code is based on an anonymous contribution by "a concerned citizen":
+ * https://dsp.stackexchange.com/questions/37714/kaiser-window-approximation
+ */
+class HyperbolicCosineWindow {
+public:
+    HyperbolicCosineWindow() {
+        setStopBandAttenuation(60);
+    }
+
+    /**
+     * @param attenuation typical values range from 30 to 90 dB
+     * @return beta
+     */
+    double setStopBandAttenuation(double attenuation) {
+        double alpha = ((-325.1e-6 * attenuation + 0.1677) * attenuation) - 3.149;
+        setAlpha(alpha);
+        return alpha;
+    }
+
+    void setAlpha(double alpha) {
+        mAlpha = alpha;
+        mInverseCoshAlpha = 1.0 / cosh(alpha);
+    }
+
+    /**
+     * @param x ranges from -1.0 to +1.0
+     */
+    double operator()(double x) {
+        double x2 = x * x;
+        if (x2 >= 1.0) return 0.0;
+        double w = mAlpha * sqrt(1.0 - x2);
+        return cosh(w) * mInverseCoshAlpha;
+    }
+
+private:
+    double mAlpha = 0.0;
+    double mInverseCoshAlpha = 1.0;
+};
+
+} /* namespace RESAMPLER_OUTER_NAMESPACE::resampler */
+
+#endif //RESAMPLER_HYPERBOLIC_COSINE_WINDOW_H