improved randShuffle as suggested by John Stark in http://code.opencv.org/issues/3730

modules/core/src/rand.cpp

@@ -748,29 +748,35 @@ namespace cv
 {
 
 template<typename T> static void
-randShuffle_( Mat& _arr, RNG& rng, double iterFactor )
+randShuffle_( Mat& _arr, RNG& rng, double )
 {
-    int sz = _arr.rows*_arr.cols, iters = cvRound(iterFactor*sz);
+    unsigned sz = (unsigned)_arr.total();
     if( _arr.isContinuous() )
     {
         T* arr = _arr.ptr<T>();
-        for( int i = 0; i < iters; i++ )
+        for( unsigned i = 0; i < sz; i++ )
         {
-            int j = (unsigned)rng % sz, k = (unsigned)rng % sz;
-            std::swap( arr[j], arr[k] );
+            unsigned j = (unsigned)rng % sz;
+            std::swap( arr[j], arr[i] );
         }
     }
     else
     {
+        CV_Assert( _arr.dims <= 2 );
         uchar* data = _arr.ptr();
         size_t step = _arr.step;
+        int rows = _arr.rows;
         int cols = _arr.cols;
-        for( int i = 0; i < iters; i++ )
+        for( int i0 = 0; i0 < rows; i0++ )
         {
-            int j1 = (unsigned)rng % sz, k1 = (unsigned)rng % sz;
-            int j0 = j1/cols, k0 = k1/cols;
-            j1 -= j0*cols; k1 -= k0*cols;
-            std::swap( ((T*)(data + step*j0))[j1], ((T*)(data + step*k0))[k1] );
+            T* p = _arr.ptr<T>(i0);
+            for( int j0 = 0; j0 < cols; j0++ )
+            {
+                unsigned k1 = (unsigned)rng % sz;
+                int i1 = (int)(k1 / cols);
+                int j1 = (int)(k1 - (unsigned)i1*(unsigned)cols);
+                std::swap( p[j0], ((T*)(data + step*i1))[j1] );
+            }
         }
     }
 }