From 0ebb3ab0ea65b8565e5a84d609258d7a573b787a Mon Sep 17 00:00:00 2001
From: Ilya Lavrenov <ilya.lavrenov@itseez.com>
Date: Tue, 28 Jan 2014 23:10:43 +0400
Subject: [PATCH] optimized createHanningWindow

---
 modules/imgproc/perf/perf_phasecorr.cpp | 22 ++++++++++++++++++++++
 modules/imgproc/src/phasecorr.cpp       | 24 ++++++++++++------------
 2 files changed, 34 insertions(+), 12 deletions(-)
 create mode 100644 modules/imgproc/perf/perf_phasecorr.cpp

diff --git a/modules/imgproc/perf/perf_phasecorr.cpp b/modules/imgproc/perf/perf_phasecorr.cpp
new file mode 100644
index 000000000..ee9d94e31
--- /dev/null
+++ b/modules/imgproc/perf/perf_phasecorr.cpp
@@ -0,0 +1,22 @@
+#include "perf_precomp.hpp"
+
+using namespace std;
+using namespace cv;
+using namespace perf;
+using namespace testing;
+using std::tr1::make_tuple;
+using std::tr1::get;
+
+typedef TestBaseWithParam<Size > CreateHanningWindowFixture;
+
+PERF_TEST_P( CreateHanningWindowFixture, CreateHanningWindow, Values(szVGA, sz1080p))
+{
+    const Size size = GetParam();
+    Mat dst(size, CV_32FC1);
+
+    declare.in(dst, WARMUP_RNG).out(dst);
+
+    TEST_CYCLE() cv::createHanningWindow(dst, size, CV_32FC1);
+
+    SANITY_CHECK(dst, 1e-6, ERROR_RELATIVE);
+}
diff --git a/modules/imgproc/src/phasecorr.cpp b/modules/imgproc/src/phasecorr.cpp
index d21a4938f..f513e84e2 100644
--- a/modules/imgproc/src/phasecorr.cpp
+++ b/modules/imgproc/src/phasecorr.cpp
@@ -576,20 +576,23 @@ void cv::createHanningWindow(OutputArray _dst, cv::Size winSize, int type)
     _dst.create(winSize, type);
     Mat dst = _dst.getMat();
 
-    int rows = dst.rows;
-    int cols = dst.cols;
+    int rows = dst.rows, cols = dst.cols;
+
+    AutoBuffer<double> _wc(cols);
+    double * const wc = (double *)_wc;
+
+    double coeff0 = 2.0 * CV_PI / (double)(cols - 1), coeff1 = 2.0f * CV_PI / (double)(rows - 1);
+    for(int j = 0; j < cols; j++)
+        wc[j] = 0.5 * (1.0 - cos(coeff0 * j));
 
     if(dst.depth() == CV_32F)
     {
         for(int i = 0; i < rows; i++)
         {
             float* dstData = dst.ptr<float>(i);
-            double wr = 0.5 * (1.0f - cos(2.0f * CV_PI * (double)i / (double)(rows - 1)));
+            double wr = 0.5 * (1.0 - cos(coeff1 * i));
             for(int j = 0; j < cols; j++)
-            {
-                double wc = 0.5 * (1.0f - cos(2.0f * CV_PI * (double)j / (double)(cols - 1)));
-                dstData[j] = (float)(wr * wc);
-            }
+                dstData[j] = (float)(wr * wc[j]);
         }
     }
     else
@@ -597,12 +600,9 @@ void cv::createHanningWindow(OutputArray _dst, cv::Size winSize, int type)
         for(int i = 0; i < rows; i++)
         {
             double* dstData = dst.ptr<double>(i);
-            double wr = 0.5 * (1.0 - cos(2.0 * CV_PI * (double)i / (double)(rows - 1)));
+            double wr = 0.5 * (1.0 - cos(coeff1 * i));
             for(int j = 0; j < cols; j++)
-            {
-                double wc = 0.5 * (1.0 - cos(2.0 * CV_PI * (double)j / (double)(cols - 1)));
-                dstData[j] = wr * wc;
-            }
+                dstData[j] = wr * wc[j];
         }
     }