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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.
*/
#define _USE_MATH_DEFINES
#include "webrtc/common_audio/window_generator.h"
#include <cmath>
#include <complex>
#include "webrtc/base/checks.h"
using std::complex;
namespace {
// Modified Bessel function of order 0 for complex inputs.
complex<float> I0(complex<float> x) {
complex<float> y = x / 3.75f;
y *= y;
return 1.0f + y * (
3.5156229f + y * (
3.0899424f + y * (
1.2067492f + y * (
0.2659732f + y * (
0.360768e-1f + y * 0.45813e-2f)))));
}
} // namespace
namespace webrtc {
void WindowGenerator::Hanning(int length, float* window) {
RTC_CHECK_GT(length, 1);
RTC_CHECK(window != nullptr);
for (int i = 0; i < length; ++i) {
window[i] = 0.5f * (1 - cosf(2 * static_cast<float>(M_PI) * i /
(length - 1)));
}
}
void WindowGenerator::KaiserBesselDerived(float alpha, size_t length,
float* window) {
RTC_CHECK_GT(length, 1U);
RTC_CHECK(window != nullptr);
const size_t half = (length + 1) / 2;
float sum = 0.0f;
for (size_t i = 0; i <= half; ++i) {
complex<float> r = (4.0f * i) / length - 1.0f;
sum += I0(static_cast<float>(M_PI) * alpha * sqrt(1.0f - r * r)).real();
window[i] = sum;
}
for (size_t i = length - 1; i >= half; --i) {
window[length - i - 1] = sqrtf(window[length - i - 1] / sum);
window[i] = window[length - i - 1];
}
if (length % 2 == 1) {
window[half - 1] = sqrtf(window[half - 1] / sum);
}
}
} // namespace webrtc
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