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Diffstat (limited to 'third_party/libwebrtc/common_audio/window_generator.cc')
-rw-r--r-- | third_party/libwebrtc/common_audio/window_generator.cc | 71 |
1 files changed, 71 insertions, 0 deletions
diff --git a/third_party/libwebrtc/common_audio/window_generator.cc b/third_party/libwebrtc/common_audio/window_generator.cc new file mode 100644 index 0000000000..da5603d9e7 --- /dev/null +++ b/third_party/libwebrtc/common_audio/window_generator.cc @@ -0,0 +1,71 @@ +/* + * 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 "common_audio/window_generator.h" + +#include <cmath> +#include <complex> + +#include "rtc_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 |