Avoid slow AudioParam automation path when possible

third_party/WebKit/Source/modules/webaudio/AudioParamTimeline.cpp

 /*
  * Copyright (C) 2011 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  *
  * 1.  Redistributions of source code must retain the above copyright
  *     notice, this list of conditions and the following disclaimer.
  * 2.  Redistributions in binary form must reproduce the above copyright
@@ skipping 383 matching lines @@
     if (!values || !(numberOfValues >= 1))
         return defaultValue;
 
     // Return default value if there are no events matching the desired time range.
     if (!m_events.size() || (endFrame / sampleRate <= m_events[0].time())) {
         for (unsigned i = 0; i < numberOfValues; ++i)
             values[i] = defaultValue;
         return defaultValue;
     }
 
+    // Optimize the case where the last event is in the past.
+    if (m_events.size() > 0) {
+        ParamEvent& lastEvent = m_events[m_events.size() - 1];
+        ParamEvent::Type lastEventType = lastEvent.getType();
+        double lastEventTime = lastEvent.time();
+        double currentTime = startFrame / sampleRate;
+
+        // If the last event is in the past and the event has ended, then we can
+        // just propagate the same value.  Except for SetTarget which lasts
+        // "forever".  SetValueCurve also has an explicit SetValue at the end of
+        // the curve, so we don't need to worry that SetValueCurve time is a
+        // start time, not an end time.
+        if (lastEventTime < currentTime && lastEventType != ParamEvent::SetTarget) {
+            // The event has finished, so just copy the default value out.
+            // Since all events are now also in the past, we can just remove all
+            // timeline events too because |defaultValue| has the expected
+            // value.
+            for (unsigned i = 0; i < numberOfValues; ++i)
+                values[i] = defaultValue;
+            m_smoothedValue = defaultValue;
+            m_events.clear();
+            return defaultValue;
+        }
+    }
+
     // Maintain a running time (frame) and index for writing the values buffer.
     size_t currentFrame = startFrame;
     unsigned writeIndex = 0;
 
     // If first event is after startFrame then fill initial part of values buffer with defaultValue
     // until we reach the first event time.
     double firstEventTime = m_events[0].time();
     if (firstEventTime > startFrame / sampleRate) {
         // |fillToFrame| is an exclusive upper bound, so use ceil() to compute the bound from the
         // firstEventTime.
@@ skipping 502 matching lines @@
     for (; writeIndex < numberOfValues; ++writeIndex)
         values[writeIndex] = value;
 
     // This value is used to set the .value attribute of the AudioParam.  it should be the last
     // computed value.
     return values[numberOfValues - 1];
 }
 
 } // namespace blink