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/*
* Copyright (c) 2015 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 "webrtc/common_audio/real_fourier_ooura.h"
#include <cmath>
#include <algorithm>
#include "webrtc/base/checks.h"
#include "webrtc/common_audio/fft4g.h"
namespace webrtc {
using std::complex;
namespace {
void Conjugate(complex<float>* array, size_t complex_length) {
std::for_each(array, array + complex_length,
[=](complex<float>& v) { v = std::conj(v); });
}
size_t ComputeWorkIpSize(size_t fft_length) {
return static_cast<size_t>(2 + std::ceil(std::sqrt(
static_cast<float>(fft_length))));
}
} // namespace
RealFourierOoura::RealFourierOoura(int fft_order)
: order_(fft_order),
length_(FftLength(order_)),
complex_length_(ComplexLength(order_)),
// Zero-initializing work_ip_ will cause rdft to initialize these work
// arrays on the first call.
work_ip_(new size_t[ComputeWorkIpSize(length_)]()),
work_w_(new float[complex_length_]()) {
RTC_CHECK_GE(fft_order, 1);
}
void RealFourierOoura::Forward(const float* src, complex<float>* dest) const {
{
// This cast is well-defined since C++11. See "Non-static data members" at:
// http://en.cppreference.com/w/cpp/numeric/complex
auto dest_float = reinterpret_cast<float*>(dest);
std::copy(src, src + length_, dest_float);
WebRtc_rdft(length_, 1, dest_float, work_ip_.get(), work_w_.get());
}
// Ooura places real[n/2] in imag[0].
dest[complex_length_ - 1] = complex<float>(dest[0].imag(), 0.0f);
dest[0] = complex<float>(dest[0].real(), 0.0f);
// Ooura returns the conjugate of the usual Fourier definition.
Conjugate(dest, complex_length_);
}
void RealFourierOoura::Inverse(const complex<float>* src, float* dest) const {
{
auto dest_complex = reinterpret_cast<complex<float>*>(dest);
// The real output array is shorter than the input complex array by one
// complex element.
const size_t dest_complex_length = complex_length_ - 1;
std::copy(src, src + dest_complex_length, dest_complex);
// Restore Ooura's conjugate definition.
Conjugate(dest_complex, dest_complex_length);
// Restore real[n/2] to imag[0].
dest_complex[0] = complex<float>(dest_complex[0].real(),
src[complex_length_ - 1].real());
}
WebRtc_rdft(length_, -1, dest, work_ip_.get(), work_w_.get());
// Ooura returns a scaled version.
const float scale = 2.0f / length_;
std::for_each(dest, dest + length_, [scale](float& v) { v *= scale; });
}
} // namespace webrtc
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