Line data    Source code

       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             : #ifndef _USE_MATH_DEFINES
      12             : #define _USE_MATH_DEFINES
      13             : #endif
      14             : 
      15             : #include "webrtc/common_audio/window_generator.h"
      16             : 
      17             : #include <cmath>
      18             : #include <complex>
      19             : 
      20             : #include "webrtc/base/checks.h"
      21             : 
      22             : using std::complex;
      23             : 
      24             : namespace {
      25             : 
      26             : // Modified Bessel function of order 0 for complex inputs.
      27           0 : complex<float> I0(complex<float> x) {
      28           0 :   complex<float> y = x / 3.75f;
      29           0 :   y *= y;
      30           0 :   return 1.0f + y * (
      31           0 :     3.5156229f + y * (
      32           0 :       3.0899424f + y * (
      33           0 :         1.2067492f + y * (
      34           0 :           0.2659732f + y * (
      35           0 :             0.360768e-1f + y * 0.45813e-2f)))));
      36             : }
      37             : 
      38             : }  // namespace
      39             : 
      40             : namespace webrtc {
      41             : 
      42           0 : void WindowGenerator::Hanning(int length, float* window) {
      43           0 :   RTC_CHECK_GT(length, 1);
      44           0 :   RTC_CHECK(window != nullptr);
      45           0 :   for (int i = 0; i < length; ++i) {
      46           0 :     window[i] = 0.5f * (1 - cosf(2 * static_cast<float>(M_PI) * i /
      47           0 :                                  (length - 1)));
      48             :   }
      49           0 : }
      50             : 
      51           0 : void WindowGenerator::KaiserBesselDerived(float alpha, size_t length,
      52             :                                           float* window) {
      53           0 :   RTC_CHECK_GT(length, 1U);
      54           0 :   RTC_CHECK(window != nullptr);
      55             : 
      56           0 :   const size_t half = (length + 1) / 2;
      57           0 :   float sum = 0.0f;
      58             : 
      59           0 :   for (size_t i = 0; i <= half; ++i) {
      60           0 :     complex<float> r = (4.0f * i) / length - 1.0f;
      61           0 :     sum += I0(static_cast<float>(M_PI) * alpha * sqrt(1.0f - r * r)).real();
      62           0 :     window[i] = sum;
      63             :   }
      64           0 :   for (size_t i = length - 1; i >= half; --i) {
      65           0 :     window[length - i - 1] = sqrtf(window[length - i - 1] / sum);
      66           0 :     window[i] = window[length - i - 1];
      67             :   }
      68           0 :   if (length % 2 == 1) {
      69           0 :     window[half - 1] = sqrtf(window[half - 1] / sum);
      70             :   }
      71           0 : }
      72             : 
      73             : }  // namespace webrtc
      74             :