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 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 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 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 48 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 64 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
