Index: media/base/moving_average.cc |
diff --git a/media/base/moving_average.cc b/media/base/moving_average.cc |
index b78f4c0e3dc90a13b00068e31c031a4e39739813..5dd140377b953e76e0d7a2b86c024ab1dad32676 100644 |
--- a/media/base/moving_average.cc |
+++ b/media/base/moving_average.cc |
@@ -9,8 +9,7 @@ |
namespace media { |
MovingAverage::MovingAverage(size_t depth) |
- : depth_(depth), count_(0), samples_(depth_) { |
-} |
+ : depth_(depth), count_(0), samples_(depth_), square_sum_us_(0) {} |
MovingAverage::~MovingAverage() { |
} |
@@ -20,6 +19,8 @@ void MovingAverage::AddSample(base::TimeDelta sample) { |
// exceeds |depth_|. |
base::TimeDelta& oldest = samples_[count_++ % depth_]; |
total_ += sample - oldest; |
+ square_sum_us_ += sample.InMicroseconds() * sample.InMicroseconds() - |
+ oldest.InMicroseconds() * oldest.InMicroseconds(); |
oldest = sample; |
} |
@@ -32,9 +33,22 @@ base::TimeDelta MovingAverage::Average() const { |
return total_ / std::min(static_cast<uint64_t>(depth_), count_); |
} |
+base::TimeDelta MovingAverage::Deviation() const { |
+ DCHECK_GT(count_, 0u); |
+ |
+ const double size = std::min(static_cast<uint64_t>(depth_), count_); |
+ const double average_us = total_.InMicroseconds() / size; |
+ double sqr_deviation_us = square_sum_us_ / size - average_us * average_us; |
+ if (sqr_deviation_us < 0) |
+ sqr_deviation_us = 0; |
+ |
+ return base::TimeDelta::FromMicroseconds(sqrt(sqr_deviation_us)); |
+} |
+ |
void MovingAverage::Reset() { |
count_ = 0; |
total_ = base::TimeDelta(); |
+ square_sum_us_ = 0; |
std::fill(samples_.begin(), samples_.end(), base::TimeDelta()); |
} |