Fixing init time error in smoothing filter.

webrtc/common_audio/smoothing_filter.cc

 /*
  *  Copyright (c) 2016 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/smoothing_filter.h"
 
 #include <cmath>
 
 namespace webrtc {
 
-SmoothingFilterImpl::SmoothingFilterImpl(int init_time_ms_, const Clock* clock)
-    : init_time_ms_(init_time_ms_),
+SmoothingFilterImpl::SmoothingFilterImpl(int init_time_ms, const Clock* clock)

[minyue-webrtc, 2016/12/21 14:10:17]

this was an old error, no actual problem, but bad style.

+    : init_time_ms_(init_time_ms),
       // Duing the initalization time, we use an increasing alpha. Specifically,
       //   alpha(n) = exp(pow(init_factor_, n)),
       // where |init_factor_| is chosen such that
       //   alpha(init_time_ms_) = exp(-1.0f / init_time_ms_),
       init_factor_(pow(init_time_ms_, 1.0f / init_time_ms_)),
       // |init_const_| is to a factor to help the calculation during
       // initialization phase.
       init_const_(1.0f / (init_time_ms_ -
                           pow(init_time_ms_, 1.0f - 1.0f / init_time_ms_))),
       clock_(clock) {
+  RTC_DCHECK_GT(init_time_ms_, 1);
   UpdateAlpha(init_time_ms_);
 }
 
 SmoothingFilterImpl::~SmoothingFilterImpl() = default;
 
 void SmoothingFilterImpl::AddSample(float sample) {
   const int64_t now_ms = clock_->TimeInMilliseconds();
 
   if (!first_sample_time_ms_) {
     // This is equivalent to assuming the filter has been receiving the same
@@ skipping 77 matching lines @@
 //     &= \exp\left(\frac{\gamma^m - \gamma^n}{1 - \gamma} \right)
 //   \end{align}
 // We know $\gamma = T^\frac{1}{T}$, where $T$ denotes init\_time\_ms\_. Then
 // $1 - \gamma$ approaches zero when $T$ increases. This can cause numerical
 // difficulties. We multiply $T$ to both numerator and denominator in the
 // fraction. See.
 //   \begin{align}
 //     \frac{\gamma^m - \gamma^n}{1 - \gamma}
 //     &= \frac{T^\frac{T-m}{T} - T^\frac{T-n}{T}}{T - T^{1-\frac{1}{T}}}
 //   \end{align}