1 /*
2  *  Copyright (c) 2014 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 #define _USE_MATH_DEFINES
12 
13 #include "webrtc/common_audio/window_generator.h"
14 
15 #include <cmath>
16 #include <complex>
17 
18 #include "webrtc/base/checks.h"
19 
20 using std::complex;
21 
22 namespace {
23 
24 // Modified Bessel function of order 0 for complex inputs.
I0(complex<float> x)25 complex<float> I0(complex<float> x) {
26   complex<float> y = x / 3.75f;
27   y *= y;
28   return 1.0f + y * (
29     3.5156229f + y * (
30       3.0899424f + y * (
31         1.2067492f + y * (
32           0.2659732f + y * (
33             0.360768e-1f + y * 0.45813e-2f)))));
34 }
35 
36 }  // namespace
37 
38 namespace webrtc {
39 
Hanning(int length,float * window)40 void WindowGenerator::Hanning(int length, float* window) {
41   RTC_CHECK_GT(length, 1);
42   RTC_CHECK(window != nullptr);
43   for (int i = 0; i < length; ++i) {
44     window[i] = 0.5f * (1 - cosf(2 * static_cast<float>(M_PI) * i /
45                                  (length - 1)));
46   }
47 }
48 
KaiserBesselDerived(float alpha,size_t length,float * window)49 void WindowGenerator::KaiserBesselDerived(float alpha, size_t length,
50                                           float* window) {
51   RTC_CHECK_GT(length, 1U);
52   RTC_CHECK(window != nullptr);
53 
54   const size_t half = (length + 1) / 2;
55   float sum = 0.0f;
56 
57   for (size_t i = 0; i <= half; ++i) {
58     complex<float> r = (4.0f * i) / length - 1.0f;
59     sum += I0(static_cast<float>(M_PI) * alpha * sqrt(1.0f - r * r)).real();
60     window[i] = sum;
61   }
62   for (size_t i = length - 1; i >= half; --i) {
63     window[length - i - 1] = sqrtf(window[length - i - 1] / sum);
64     window[i] = window[length - i - 1];
65   }
66   if (length % 2 == 1) {
67     window[half - 1] = sqrtf(window[half - 1] / sum);
68   }
69 }
70 
71 }  // namespace webrtc
72 
73