From 0be18aca81aa154f4020bf0296d93765463fb39c Mon Sep 17 00:00:00 2001
From: Maksim Shabunin <Maksim.Shabunin@itseez.com>
Date: Fri, 8 Aug 2014 16:58:35 +0400
Subject: [PATCH] Revert "Allows to choose orthogonal sub-vectors for LSH
 without using a static table among LshTable instances"

This reverts commit e63d7de87c3565555e4a73220a465ed39488160d.
---
 modules/flann/include/opencv2/flann/lsh_index.h | 14 +-----------
 modules/flann/include/opencv2/flann/lsh_table.h | 30 ++++++++++++++++++-------
 2 files changed, 23 insertions(+), 21 deletions(-)

diff --git a/modules/flann/include/opencv2/flann/lsh_index.h b/modules/flann/include/opencv2/flann/lsh_index.h
index 2530a01..4d4670e 100644
--- a/modules/flann/include/opencv2/flann/lsh_index.h
+++ b/modules/flann/include/opencv2/flann/lsh_index.h
@@ -109,22 +109,10 @@ public:
      */
     void buildIndex()
     {
-        std::vector<size_t> indices(feature_size_ * CHAR_BIT);
-
         tables_.resize(table_number_);
         for (unsigned int i = 0; i < table_number_; ++i) {
-
-            //re-initialize the random indices table that the LshTable will use to pick its sub-dimensions
-            if( (indices.size() == feature_size_ * CHAR_BIT) || (indices.size() < key_size_) )
-            {
-              indices.resize( feature_size_ * CHAR_BIT );
-              for (size_t i = 0; i < feature_size_ * CHAR_BIT; ++i)
-                  indices[i] = i;
-              std::random_shuffle(indices.begin(), indices.end());
-            }
-
             lsh::LshTable<ElementType>& table = tables_[i];
-            table = lsh::LshTable<ElementType>(feature_size_, key_size_, indices);
+            table = lsh::LshTable<ElementType>(feature_size_, key_size_);
 
             // Add the features to the table
             table.add(dataset_);
diff --git a/modules/flann/include/opencv2/flann/lsh_table.h b/modules/flann/include/opencv2/flann/lsh_table.h
index 956e14e..5da0e3f 100644
--- a/modules/flann/include/opencv2/flann/lsh_table.h
+++ b/modules/flann/include/opencv2/flann/lsh_table.h
@@ -153,7 +153,7 @@ public:
      * @param feature_size is the size of the feature (considered as a ElementType[])
      * @param key_size is the number of bits that are turned on in the feature
      */
-    LshTable(unsigned int /*feature_size*/, unsigned int /*key_size*/, std::vector<size_t> & /*indices*/)
+    LshTable(unsigned int /*feature_size*/, unsigned int /*key_size*/)
     {
         std::cerr << "LSH is not implemented for that type" << std::endl;
         assert(0);
@@ -339,20 +339,34 @@ private:
 // Specialization for unsigned char
 
 template<>
-inline LshTable<unsigned char>::LshTable( unsigned int feature_size,
-                                          unsigned int subsignature_size,
-                                          std::vector<size_t> & indices  )
+inline LshTable<unsigned char>::LshTable(unsigned int feature_size, unsigned int subsignature_size)
 {
     initialize(subsignature_size);
     // Allocate the mask
     mask_ = std::vector<size_t>((size_t)ceil((float)(feature_size * sizeof(char)) / (float)sizeof(size_t)), 0);
 
+    // A bit brutal but fast to code
+    static std::vector<size_t>* indices = NULL;
+
+    //Ensure the Nth bit will be selected only once among the different LshTables
+    //to avoid having two different tables with signatures sharing many dimensions/many bits
+    if( indices == NULL )
+    {
+        indices = new std::vector<size_t>( feature_size * CHAR_BIT );
+    }
+    else if( indices->size() < key_size_ )
+    {
+      indices->resize( feature_size * CHAR_BIT );
+      for (size_t i = 0; i < feature_size * CHAR_BIT; ++i) {
+          (*indices)[i] = i;
+      }
+      std::random_shuffle(indices->begin(), indices->end());
+    }
+
     // Generate a random set of order of subsignature_size_ bits
     for (unsigned int i = 0; i < key_size_; ++i) {
-        //Ensure the Nth bit will be selected only once among the different LshTables
-        //to avoid having two different tables with signatures sharing many dimensions/many bits
-        size_t index = indices[0];
-        indices.erase( indices.begin() );
+        size_t index = (*indices)[0];
+        indices->erase( indices->begin() );
 
         // Set that bit in the mask
         size_t divisor = CHAR_BIT * sizeof(size_t);
-- 
2.7.4