Merge remote-tracking branch 'upstream/3.4' into merge-3.4

Author: alalek

modules/stereo/include/opencv2/stereo/descriptor.hpp

@@ -222,7 +222,7 @@ namespace cv
                     for (int j = n2 + 2; j <= width - n2 - 2; j++)
                     {
                         int c[nr_img];
-                        memset(c,0,nr_img);
+                        memset(c, 0, sizeof(c[0]) * nr_img);
                         for(int step = step_start; step <= step_end; step += step_inc)
                         {
                             for (int ii = - n2; ii <= + n2_stop; ii += step)

modules/xfeatures2d/src/sift.cpp

@@ -1147,19 +1147,20 @@ void SIFT_Impl::detectAndCompute(InputArray _image, InputArray _mask,
     }
 
     Mat base = createInitialImage(image, firstOctave < 0, (float)sigma);
-    std::vector<Mat> gpyr, dogpyr;
+    std::vector<Mat> gpyr;
     int nOctaves = actualNOctaves > 0 ? actualNOctaves : cvRound(std::log( (double)std::min( base.cols, base.rows ) ) / std::log(2.) - 2) - firstOctave;
 
     //double t, tf = getTickFrequency();
     //t = (double)getTickCount();
     buildGaussianPyramid(base, gpyr, nOctaves);
-    buildDoGPyramid(gpyr, dogpyr);
 
     //t = (double)getTickCount() - t;
     //printf("pyramid construction time: %g\n", t*1000./tf);
 
     if( !useProvidedKeypoints )
     {
+        std::vector<Mat> dogpyr;
+        buildDoGPyramid(gpyr, dogpyr);
         //t = (double)getTickCount();
         findScaleSpaceExtrema(gpyr, dogpyr, keypoints);
         KeyPointsFilter::removeDuplicatedSorted( keypoints );