diff --git a/fastlib/trunk/contrib/dongryel/thesis_research/core/math/math_lib.h b/fastlib/trunk/contrib/dongryel/thesis_research/core/math/math_lib.h
index 4b67f3cb1a..0feda64013 100644
--- a/fastlib/trunk/contrib/dongryel/thesis_research/core/math/math_lib.h
+++ b/fastlib/trunk/contrib/dongryel/thesis_research/core/math/math_lib.h
@@ -202,25 +202,40 @@ void RandomCombination(
   }
 }
 
+/** @brief Implements Algorithm 1 in "Fast Construction of $k$-Nearest
+ *         Neighbor Graphs for Point Clouds" by Connor and Kumar, TVCG
+ *         2009.
+ */
 template<typename T>
 int XorMsb(T a, T b) {
 
-  union {
+  typedef union {
     T float_rep_;
     int int_rep_;
   } float_helper;
 
-  // The number of Mantissa bits.
-  int num_mantissa_bits = std::numeric_limits<T>::digits();
   int a_exp, b_exp;
-  union float_helper a_mantissa, b_mantissa;
+  float_helper a_mantissa, b_mantissa;
   a_mantissa.float_rep_ = frexp(a, &a_exp);
   b_mantissa.float_rep_ = frexp(b, &b_exp);
-  if(false) {
-    a_exp -= 0;
-    return a_exp;
+  if(a_exp == b_exp) {
+
+    // Take the XOR of the two Mantissa bit representations and find
+    // the most significant bit.
+    int a_mantissa_xor_b_mantissa = a_mantissa.int_rep_ ^ b_mantissa.int_rep_;
+    int most_significant_bit = 0;
+    int shift_bit = 1;
+    int num_bits_in_int = std::numeric_limits<int>::digits;
+    for(int i = 0; i <= num_bits_in_int; i++) {
+      if((shift_bit & a_mantissa_xor_b_mantissa) != 0) {
+        most_significant_bit = shift_bit;
+      }
+      shift_bit = shift_bit << 1;
+    }
+    return a_exp - shift_bit;
   }
-  if(false) {
+  if(b_exp < a_exp) {
+    return a_exp;
   }
   else {
     return b_exp;
@@ -235,7 +250,7 @@ inline bool MortonOrderPoints(const PointType &a, const PointType &b) {
   int selected_dim = 0;
 
   for(int d = 0; d < a.length(); d++) {
-    int y = XorMsb(a[d], b[d]);
+    long int y = XorMsb(a[d], b[d]);
     if(x < y) {
       x = y;
       selected_dim = d;
diff --git a/fastlib/trunk/contrib/dongryel/thesis_research/core/tree/distributed_tree.test.cc b/fastlib/trunk/contrib/dongryel/thesis_research/core/tree/distributed_tree.test.cc
index ac767eac73..dae987b767 100644
--- a/fastlib/trunk/contrib/dongryel/thesis_research/core/tree/distributed_tree.test.cc
+++ b/fastlib/trunk/contrib/dongryel/thesis_research/core/tree/distributed_tree.test.cc
@@ -92,17 +92,27 @@ class TestDistributedTree {
 };
 };
 
-BOOST_AUTO_TEST_SUITE(TestSuiteDistributedTree)
-BOOST_AUTO_TEST_CASE(TestCaseDistributedTree) {
+int main(int argc, char *argv[]) {
+
+  // Initialize boost MPI.
+  boost::mpi::environment env(argc, argv);
+  boost::mpi::communicator world;
 
   // Tree type: hard-coded for a metric tree.
-  typedef core::table::Table <
-  core::tree::GenMetricTree<core::tree::AbstractStatistic> > TableType;
+  typedef core::tree::GenMetricTree<core::tree::AbstractStatistic> TreeSpecType;
+  typedef core::table::Table <TreeSpecType> TableType;
+  typedef core::table::DistributedTable<TreeSpecType> DistributedTableType;
+
+  DistributedTableType distributed_table;
+  core::tree::DistributedTreeBuilder<DistributedTableType> builder;
+  builder.Init(distributed_table, 0.2);
+  core::metric_kernels::LMetric<2> l2_metric;
+  builder.Build(l2_metric, world);
 
   // Call the tests.
   core::tree::TestDistributedTree<TableType> tree_test;
   tree_test.StressTestMain();
 
   std::cout << "All tests passed!\n";
+  return 0;
 }
-BOOST_AUTO_TEST_SUITE_END()
diff --git a/fastlib/trunk/contrib/dongryel/thesis_research/core/tree/distributed_tree_builder.h b/fastlib/trunk/contrib/dongryel/thesis_research/core/tree/distributed_tree_builder.h
index b6050ebce8..5652b894c4 100644
--- a/fastlib/trunk/contrib/dongryel/thesis_research/core/tree/distributed_tree_builder.h
+++ b/fastlib/trunk/contrib/dongryel/thesis_research/core/tree/distributed_tree_builder.h
@@ -31,6 +31,12 @@ class DistributedTreeBuilder {
 
   private:
 
+    static bool MortonOrderNodes_(TreeType *first_node, TreeType *second_node) {
+      return
+        core::math::MortonOrderPoints(
+          first_node->bound().center(), second_node->bound().center());
+    }
+
     void AugmentNodes_(
       boost::mpi::communicator &world,
       const typename TreeType::BoundType &root_bound,
@@ -57,7 +63,6 @@ class DistributedTreeBuilder {
         }
         tmp_point_alias = (1.0 / static_cast<double>(num_samples)) *
                           tmp_point_alias;
-        tmp_point_alias = 0.5 * (tmp_point_alias + random_point_on_surface);
         top_leaf_nodes.push_back(new TreeType());
         top_leaf_nodes[ top_leaf_nodes.size() - 1 ]->bound().center().Copy(
           tmp_point);
@@ -88,7 +93,7 @@ class DistributedTreeBuilder {
       // send to the master. This is a MPI gather operation.
       TableType sampled_table;
       std::vector<int> sampled_indices;
-      SelectSubset_(sampling_rate_, &sampled_indices);
+      SelectSubset_(&sampled_indices);
 
       // Send the number of points chosen in this process to the
       // master so that the master can allocate the appropriate amount
@@ -123,8 +128,13 @@ class DistributedTreeBuilder {
         if(top_leaf_nodes_out->size() <
             static_cast<unsigned int>(world.size())) {
           AugmentNodes_(
-            world, sampled_table.get_tree()->bound(), top_leaf_nodes_out);
+            world, sampled_table.get_tree()->bound(), *top_leaf_nodes_out);
         }
+
+        // Sort the nodes by Z-ordering their centroids.
+        std::sort(
+          top_leaf_nodes_out->begin(), top_leaf_nodes_out->end(),
+          MortonOrderNodes_);
       }
       boost::mpi::broadcast(world, *top_leaf_nodes_out, 0);
     }
@@ -157,7 +167,7 @@ class DistributedTreeBuilder {
       sampling_rate_ = sampling_rate_in;
     }
 
-    void BuildTree(
+    void Build(
       const core::metric_kernels::AbstractMetric &metric_in,
       boost::mpi::communicator &world) {
 
@@ -165,8 +175,6 @@ class DistributedTreeBuilder {
       std::vector<TreeType *> top_leaf_nodes;
       BuildSampleTree_(metric_in, world, &top_leaf_nodes);
 
-      // Sort the top leaf nodes by their Z-ordering.
-
     }
 };
 };