flann: use OpenCV theRNG()

std::rand() has no thread-safe guarantee.

backport commit: 147f3ebf

modules/flann/include/opencv2/flann/kdtree_index.h

@@ -132,7 +132,12 @@ public:
         /* Construct the randomized trees. */
         for (int i = 0; i < trees_; i++) {
             /* Randomize the order of vectors to allow for unbiased sampling. */
+#ifndef OPENCV_FLANN_USE_STD_RAND
+            cv::randShuffle(vind_);
+#else
             std::random_shuffle(vind_.begin(), vind_.end());
+#endif
+
             tree_roots_[i] = divideTree(&vind_[0], int(size_) );
         }
     }

modules/flann/include/opencv2/flann/lsh_index.h

@@ -136,7 +136,12 @@ public:
               indices.resize( feature_size_ * CHAR_BIT );
               for (size_t j = 0; j < feature_size_ * CHAR_BIT; ++j)
                   indices[j] = j;
+
+#ifndef OPENCV_FLANN_USE_STD_RAND
+              cv::randShuffle(indices);
+#else
               std::random_shuffle(indices.begin(), indices.end());
+#endif
             }
 
             lsh::LshTable<ElementType>& table = tables_[i];

modules/flann/include/opencv2/flann/random.h

@@ -40,13 +40,31 @@
 namespace cvflann
 {
 
+inline int rand()
+{
+#ifndef OPENCV_FLANN_USE_STD_RAND
+#   if INT_MAX == RAND_MAX
+    int v = cv::theRNG().next() & INT_MAX;
+#   else
+    int v = cv::theRNG().uniform(0, RAND_MAX + 1);
+#   endif
+#else
+    int v = std::rand();
+#endif // OPENCV_FLANN_USE_STD_RAND
+    return v;
+}
+
 /**
  * Seeds the random number generator
  *  @param seed Random seed
  */
 inline void seed_random(unsigned int seed)
 {
-    srand(seed);
+#ifndef OPENCV_FLANN_USE_STD_RAND
+    cv::theRNG() = cv::RNG(seed);
+#else
+    std::srand(seed);
+#endif
 }
 
 /*
@@ -60,7 +78,7 @@ inline void seed_random(unsigned int seed)
  */
 inline double rand_double(double high = 1.0, double low = 0)
 {
-    return low + ((high-low) * (std::rand() / (RAND_MAX + 1.0)));
+    return low + ((high-low) * (rand() / (RAND_MAX + 1.0)));
 }
 
 /**
@@ -71,7 +89,7 @@ inline double rand_double(double high = 1.0, double low = 0)
  */
 inline int rand_int(int high = RAND_MAX, int low = 0)
 {
-    return low + (int) ( double(high-low) * (std::rand() / (RAND_MAX + 1.0)));
+    return low + (int) ( double(high-low) * (rand() / (RAND_MAX + 1.0)));
 }
 
 /**
@@ -107,7 +125,11 @@ public:
         for (int i = 0; i < size_; ++i) vals_[i] = i;
 
         // shuffle the elements in the array
+#ifndef OPENCV_FLANN_USE_STD_RAND
+        cv::randShuffle(vals_);
+#else
         std::random_shuffle(vals_.begin(), vals_.end());
+#endif
 
         counter_ = 0;
     }