1/*
2 *  Copyright (c) 2015 The WebRTC project authors. All Rights Reserved.
3 *
4 *  Use of this source code is governed by a BSD-style license
5 *  that can be found in the LICENSE file in the root of the source
6 *  tree. An additional intellectual property rights grant can be found
7 *  in the file PATENTS.  All contributing project authors may
8 *  be found in the AUTHORS file in the root of the source tree.
9 */
10
11#include "webrtc/common_audio/real_fourier_ooura.h"
12
13#include <cmath>
14#include <algorithm>
15
16#include "webrtc/base/checks.h"
17#include "webrtc/common_audio/fft4g.h"
18
19namespace webrtc {
20
21using std::complex;
22
23namespace {
24
25void Conjugate(complex<float>* array, size_t complex_length) {
26  std::for_each(array, array + complex_length,
27                [=](complex<float>& v) { v = std::conj(v); });
28}
29
30size_t ComputeWorkIpSize(size_t fft_length) {
31  return static_cast<size_t>(2 + std::ceil(std::sqrt(
32      static_cast<float>(fft_length))));
33}
34
35}  // namespace
36
37RealFourierOoura::RealFourierOoura(int fft_order)
38    : order_(fft_order),
39      length_(FftLength(order_)),
40      complex_length_(ComplexLength(order_)),
41      // Zero-initializing work_ip_ will cause rdft to initialize these work
42      // arrays on the first call.
43      work_ip_(new size_t[ComputeWorkIpSize(length_)]()),
44      work_w_(new float[complex_length_]()) {
45  RTC_CHECK_GE(fft_order, 1);
46}
47
48void RealFourierOoura::Forward(const float* src, complex<float>* dest) const {
49  {
50    // This cast is well-defined since C++11. See "Non-static data members" at:
51    // http://en.cppreference.com/w/cpp/numeric/complex
52    auto dest_float = reinterpret_cast<float*>(dest);
53    std::copy(src, src + length_, dest_float);
54    WebRtc_rdft(length_, 1, dest_float, work_ip_.get(), work_w_.get());
55  }
56
57  // Ooura places real[n/2] in imag[0].
58  dest[complex_length_ - 1] = complex<float>(dest[0].imag(), 0.0f);
59  dest[0] = complex<float>(dest[0].real(), 0.0f);
60  // Ooura returns the conjugate of the usual Fourier definition.
61  Conjugate(dest, complex_length_);
62}
63
64void RealFourierOoura::Inverse(const complex<float>* src, float* dest) const {
65  {
66    auto dest_complex = reinterpret_cast<complex<float>*>(dest);
67    // The real output array is shorter than the input complex array by one
68    // complex element.
69    const size_t dest_complex_length = complex_length_ - 1;
70    std::copy(src, src + dest_complex_length, dest_complex);
71    // Restore Ooura's conjugate definition.
72    Conjugate(dest_complex, dest_complex_length);
73    // Restore real[n/2] to imag[0].
74    dest_complex[0] = complex<float>(dest_complex[0].real(),
75                                     src[complex_length_ - 1].real());
76  }
77
78  WebRtc_rdft(length_, -1, dest, work_ip_.get(), work_w_.get());
79
80  // Ooura returns a scaled version.
81  const float scale = 2.0f / length_;
82  std::for_each(dest, dest + length_, [scale](float& v) { v *= scale; });
83}
84
85}  // namespace webrtc
86