1 files changed, 142 insertions, 0 deletions
diff --git a/Source/cmComputeComponentGraph.cxx b/Source/cmComputeComponentGraph.cxx
new file mode 100644
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--- /dev/null
+++ b/Source/cmComputeComponentGraph.cxx
@@ -0,0 +1,142 @@
+/*============================================================================
+  CMake - Cross Platform Makefile Generator
+  Copyright 2000-2009 Kitware, Inc., Insight Software Consortium
+
+  Distributed under the OSI-approved BSD License (the "License");
+  see accompanying file Copyright.txt for details.
+
+  This software is distributed WITHOUT ANY WARRANTY; without even the
+  implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
+  See the License for more information.
+============================================================================*/
+#include "cmComputeComponentGraph.h"
+
+#include <algorithm>
+
+#include <assert.h>
+
+cmComputeComponentGraph::cmComputeComponentGraph(Graph const& input)
+  : InputGraph(input)
+{
+  // Identify components.
+  this->Tarjan();
+
+  // Compute the component graph.
+  this->ComponentGraph.resize(0);
+  this->ComponentGraph.resize(this->Components.size());
+  this->TransferEdges();
+}
+
+cmComputeComponentGraph::~cmComputeComponentGraph()
+{
+}
+
+void cmComputeComponentGraph::Tarjan()
+{
+  int n = static_cast<int>(this->InputGraph.size());
+  TarjanEntry entry = { 0, 0 };
+  this->TarjanEntries.resize(0);
+  this->TarjanEntries.resize(n, entry);
+  this->TarjanComponents.resize(0);
+  this->TarjanComponents.resize(n, -1);
+  this->TarjanWalkId = 0;
+  this->TarjanVisited.resize(0);
+  this->TarjanVisited.resize(n, 0);
+  for (int i = 0; i < n; ++i) {
+    // Start a new DFS from this node if it has never been visited.
+    if (!this->TarjanVisited[i]) {
+      assert(this->TarjanStack.empty());
+      ++this->TarjanWalkId;
+      this->TarjanIndex = 0;
+      this->TarjanVisit(i);
+    }
+  }
+}
+
+void cmComputeComponentGraph::TarjanVisit(int i)
+{
+  // We are now visiting this node.
+  this->TarjanVisited[i] = this->TarjanWalkId;
+
+  // Initialize the entry.
+  this->TarjanEntries[i].Root = i;
+  this->TarjanComponents[i] = -1;
+  this->TarjanEntries[i].VisitIndex = ++this->TarjanIndex;
+  this->TarjanStack.push(i);
+
+  // Follow outgoing edges.
+  EdgeList const& nl = this->InputGraph[i];
+  for (EdgeList::const_iterator ni = nl.begin(); ni != nl.end(); ++ni) {
+    int j = *ni;
+
+    // Ignore edges to nodes that have been reached by a previous DFS
+    // walk.  Since we did not reach the current node from that walk
+    // it must not belong to the same component and it has already
+    // been assigned to a component.
+    if (this->TarjanVisited[j] > 0 &&
+        this->TarjanVisited[j] < this->TarjanWalkId) {
+      continue;
+    }
+
+    // Visit the destination if it has not yet been visited.
+    if (!this->TarjanVisited[j]) {
+      this->TarjanVisit(j);
+    }
+
+    // If the destination has not yet been assigned to a component,
+    // check if it has a better root for the current object.
+    if (this->TarjanComponents[j] < 0) {
+      if (this->TarjanEntries[this->TarjanEntries[j].Root].VisitIndex <
+          this->TarjanEntries[this->TarjanEntries[i].Root].VisitIndex) {
+        this->TarjanEntries[i].Root = this->TarjanEntries[j].Root;
+      }
+    }
+  }
+
+  // Check if we have found a component.
+  if (this->TarjanEntries[i].Root == i) {
+    // Yes.  Create it.
+    int c = static_cast<int>(this->Components.size());
+    this->Components.push_back(NodeList());
+    NodeList& component = this->Components[c];
+
+    // Populate the component list.
+    int j;
+    do {
+      // Get the next member of the component.
+      j = this->TarjanStack.top();
+      this->TarjanStack.pop();
+
+      // Assign the member to the component.
+      this->TarjanComponents[j] = c;
+      this->TarjanEntries[j].Root = i;
+
+      // Store the node in its component.
+      component.push_back(j);
+    } while (j != i);
+
+    // Sort the component members for clarity.
+    std::sort(component.begin(), component.end());
+  }
+}
+
+void cmComputeComponentGraph::TransferEdges()
+{
+  // Map inter-component edges in the original graph to edges in the
+  // component graph.
+  int n = static_cast<int>(this->InputGraph.size());
+  for (int i = 0; i < n; ++i) {
+    int i_component = this->TarjanComponents[i];
+    EdgeList const& nl = this->InputGraph[i];
+    for (EdgeList::const_iterator ni = nl.begin(); ni != nl.end(); ++ni) {
+      int j = *ni;
+      int j_component = this->TarjanComponents[j];
+      if (i_component != j_component) {
+        // We do not attempt to combine duplicate edges, but instead
+        // store the inter-component edges with suitable multiplicity.
+        this->ComponentGraph[i_component].push_back(
+          cmGraphEdge(j_component, ni->IsStrong()));
+      }
+    }
+  }
+}