[x265] [PATCH 2 of 2] rc: Remove the redundant calculation on slidingWindow

[Ximing Cheng]

# HG changeset patch
# User Ximing Cheng <ximingcheng at tencent.com>
# Date 1444616617 -28800
#      Mon Oct 12 10:23:37 2015 +0800
# Node ID 0d1cfbb2716edcf9ba5b8ccc8b0fd585f4de59d7
# Parent  667253981f61f18c36bf5c7f607fbf6ea8cc6474
rc: Remove the redundant calculation on slidingWindow

diff -r 667253981f61 -r 0d1cfbb2716e source/encoder/ratecontrol.cpp
--- a/source/encoder/ratecontrol.cpp	Mon Oct 12 10:18:55 2015 +0800
+++ b/source/encoder/ratecontrol.cpp	Mon Oct 12 10:23:37 2015 +0800
@@ -219,6 +219,7 @@
     m_cutreeStatFileOut = m_cutreeStatFileIn = NULL;
     m_rce2Pass = NULL;
     m_lastBsliceSatdCost = 0;
+    m_movingAvgSum = 0.0;
 
     // vbv initialization
     m_param->rc.vbvBufferSize = x265_clip3(0, 2000000, m_param->rc.vbvBufferSize);
@@ -1347,18 +1348,28 @@
     {
         if (m_isAbr)
         {
-            double slidingWindowCplxSum = 0;
-            int start = m_sliderPos > s_slidingWindowFrames ?  m_sliderPos : 0;
-            for (int cnt = 0; cnt < s_slidingWindowFrames; cnt++, start++)
+            int pos = m_sliderPos % s_slidingWindowFrames;
+            int addPos = (pos + s_slidingWindowFrames - 1) % s_slidingWindowFrames;
+            if (m_sliderPos > s_slidingWindowFrames)
             {
-                int pos = start % s_slidingWindowFrames;
-                slidingWindowCplxSum *= 0.5;
-                if (!m_satdCostWindow[pos])
-                    break;
-                slidingWindowCplxSum += m_satdCostWindow[pos];
+                const static double base = pow(0.5, s_slidingWindowFrames - 1);
+                m_movingAvgSum -= m_lastRemovedSatdCost * base;
+                m_movingAvgSum *= 0.5;
+                m_movingAvgSum += m_satdCostWindow[addPos];
             }
-            rce->movingAvgSum = slidingWindowCplxSum;
-            m_satdCostWindow[m_sliderPos % s_slidingWindowFrames] = rce->lastSatd;
+            else if (m_sliderPos == s_slidingWindowFrames)
+            {
+                m_movingAvgSum += m_satdCostWindow[addPos];
+            }
+            else if (m_sliderPos > 0)
+            {
+                m_movingAvgSum += m_satdCostWindow[addPos];
+                m_movingAvgSum *= 0.5;
+            }
+
+            rce->movingAvgSum = m_movingAvgSum;
+            m_lastRemovedSatdCost = m_satdCostWindow[pos];
+            m_satdCostWindow[pos] = rce->lastSatd;
             m_sliderPos++;
         }
     }
diff -r 667253981f61 -r 0d1cfbb2716e source/encoder/ratecontrol.h
--- a/source/encoder/ratecontrol.h	Mon Oct 12 10:18:55 2015 +0800
+++ b/source/encoder/ratecontrol.h	Mon Oct 12 10:23:37 2015 +0800
@@ -167,6 +167,8 @@
     int64_t m_satdCostWindow[50];
     int64_t m_encodedBitsWindow[50];
     int     m_sliderPos;
+    int64_t m_lastRemovedSatdCost;
+    double  m_movingAvgSum;
 
     /* To detect a pattern of low detailed static frames in single pass ABR using satdcosts */
     int64_t m_lastBsliceSatdCost;