First-order Ambisonic renderer, optimized for AVX2

libraries/audio/src/AudioFOA.h

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+//
+//  AudioFOA.h
+//  libraries/audio/src
+//
+//  Created by Ken Cooke on 10/28/16.
+//  Copyright 2016 High Fidelity, Inc.
+//
+//  Distributed under the Apache License, Version 2.0.
+//  See the accompanying file LICENSE or http://www.apache.org/licenses/LICENSE-2.0.html
+//
+
+#ifndef hifi_AudioFOA_h
+#define hifi_AudioFOA_h
+
+#include <stdint.h>
+
+static const int FOA_TAPS = 273;    // FIR coefs
+static const int FOA_NFFT = 512;    // FFT length
+static const int FOA_OVERLAP = FOA_TAPS - 1;
+static const int FOA_TABLES = 25;   // number of HRTF subjects
+
+static const int FOA_BLOCK = 240;   // block processing size
+
+static const float FOA_GAIN = 1.0f; // FOA global gain adjustment
+
+static_assert((FOA_BLOCK + FOA_OVERLAP) == FOA_NFFT, "FFT convolution requires L+M-1 == NFFT");
+
+class AudioFOA {
+
+public:
+    AudioFOA() {
+        // identity matrix
+        _rotationState[0][0] = 1.0f;
+        _rotationState[1][1] = 1.0f;
+        _rotationState[2][2] = 1.0f;
+    };
+
+    //
+    // input: interleaved First-Order Ambisonic source
+    // output: interleaved stereo mix buffer (accumulates into existing output)
+    // index: HRTF subject index
+    // qw, qx, qy, qz: normalized quaternion for orientation
+    // gain: gain factor for volume control
+    // numFrames: must be FOA_BLOCK in this version
+    //
+    void render(int16_t* input, float* output, int index, float qw, float qx, float qy, float qz, float gain, int numFrames);
+
+private:
+    AudioFOA(const AudioFOA&) = delete;
+    AudioFOA& operator=(const AudioFOA&) = delete;
+
+    // For best cache utilization when processing thousands of instances, only
+    // the minimum persistant state is stored here. No coefs or work buffers.
+
+    // input history, for overlap-save
+    float _fftState[4][FOA_OVERLAP] = {};
+
+    // orientation history
+    float _rotationState[3][3] = {};
+};
+
+#endif // AudioFOA_h