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+/*
+ *  Copyright (c) 2014 The WebRTC project authors. All Rights Reserved.
+ *
+ *  Use of this source code is governed by a BSD-style license
+ *  that can be found in the LICENSE file in the root of the source
+ *  tree. An additional intellectual property rights grant can be found
+ *  in the file PATENTS.  All contributing project authors may
+ *  be found in the AUTHORS file in the root of the source tree.
+ */
+
+#ifndef COMMON_AUDIO_REAL_FOURIER_H_
+#define COMMON_AUDIO_REAL_FOURIER_H_
+
+#include <stddef.h>
+
+#include <complex>
+#include <memory>
+
+#include "rtc_base/memory/aligned_malloc.h"
+
+// Uniform interface class for the real DFT and its inverse, for power-of-2
+// input lengths. Also contains helper functions for buffer allocation, taking
+// care of any memory alignment requirements the underlying library might have.
+
+namespace webrtc {
+
+class RealFourier {
+ public:
+  // Shorthand typenames for the scopers used by the buffer allocation helpers.
+  typedef std::unique_ptr<float[], AlignedFreeDeleter> fft_real_scoper;
+  typedef std::unique_ptr<std::complex<float>[], AlignedFreeDeleter>
+      fft_cplx_scoper;
+
+  // The alignment required for all input and output buffers, in bytes.
+  static const size_t kFftBufferAlignment;
+
+  // Construct a wrapper instance for the given input order, which must be
+  // between 1 and kMaxFftOrder, inclusively.
+  static std::unique_ptr<RealFourier> Create(int fft_order);
+  virtual ~RealFourier() {}
+
+  // Helper to compute the smallest FFT order (a power of 2) which will contain
+  // the given input length.
+  static int FftOrder(size_t length);
+
+  // Helper to compute the input length from the FFT order.
+  static size_t FftLength(int order);
+
+  // Helper to compute the exact length, in complex floats, of the transform
+  // output (i.e. |2^order / 2 + 1|).
+  static size_t ComplexLength(int order);
+
+  // Buffer allocation helpers. The buffers are large enough to hold `count`
+  // floats/complexes and suitably aligned for use by the implementation.
+  // The returned scopers are set up with proper deleters; the caller owns
+  // the allocated memory.
+  static fft_real_scoper AllocRealBuffer(int count);
+  static fft_cplx_scoper AllocCplxBuffer(int count);
+
+  // Main forward transform interface. The output array need only be big
+  // enough for |2^order / 2 + 1| elements - the conjugate pairs are not
+  // returned. Input and output must be properly aligned (e.g. through
+  // AllocRealBuffer and AllocCplxBuffer) and input length must be
+  // |2^order| (same as given at construction time).
+  virtual void Forward(const float* src, std::complex<float>* dest) const = 0;
+
+  // Inverse transform. Same input format as output above, conjugate pairs
+  // not needed.
+  virtual void Inverse(const std::complex<float>* src, float* dest) const = 0;
+
+  virtual int order() const = 0;
+};
+
+}  // namespace webrtc
+
+#endif  // COMMON_AUDIO_REAL_FOURIER_H_