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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.
#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 {
// 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>
// 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