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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 
19 namespace webrtc {
20 
21 using std::complex;
22 
23 namespace {
24 
Conjugate(complex<float> * array,size_t complex_length)25 void 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 
ComputeWorkIpSize(size_t fft_length)30 size_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 
RealFourierOoura(int fft_order)37 RealFourierOoura::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 
Forward(const float * src,complex<float> * dest) const48 void 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 
Inverse(const complex<float> * src,float * dest) const64 void 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