feat():initial version

install/boost_1_75_0/include/boost/graph/relax.hpp

@@ -0,0 +1,135 @@
+//=======================================================================
+// Copyright 1997, 1998, 1999, 2000 University of Notre Dame.
+// Authors: Andrew Lumsdaine, Lie-Quan Lee, Jeremy G. Siek,
+//
+// Distributed under the Boost Software License, Version 1.0. (See
+// accompanying file LICENSE_1_0.txt or copy at
+// http://www.boost.org/LICENSE_1_0.txt)
+//=======================================================================
+#ifndef BOOST_GRAPH_RELAX_HPP
+#define BOOST_GRAPH_RELAX_HPP
+
+#include <functional>
+#include <boost/limits.hpp> // for numeric limits
+#include <boost/graph/graph_traits.hpp>
+#include <boost/property_map/property_map.hpp>
+
+namespace boost
+{
+
+// The following version of the plus functor prevents
+// problems due to overflow at positive infinity.
+
+template < class T > struct closed_plus
+{
+    const T inf;
+
+    closed_plus() : inf((std::numeric_limits< T >::max)()) {}
+    closed_plus(T inf) : inf(inf) {}
+
+    T operator()(const T& a, const T& b) const
+    {
+        using namespace std;
+        if (a == inf)
+            return inf;
+        if (b == inf)
+            return inf;
+        return a + b;
+    }
+};
+
+template < class Graph, class WeightMap, class PredecessorMap,
+    class DistanceMap, class BinaryFunction, class BinaryPredicate >
+bool relax(typename graph_traits< Graph >::edge_descriptor e, const Graph& g,
+    const WeightMap& w, PredecessorMap& p, DistanceMap& d,
+    const BinaryFunction& combine, const BinaryPredicate& compare)
+{
+    typedef typename graph_traits< Graph >::directed_category DirCat;
+    bool is_undirected = is_same< DirCat, undirected_tag >::value;
+    typedef typename graph_traits< Graph >::vertex_descriptor Vertex;
+    Vertex u = source(e, g), v = target(e, g);
+    typedef typename property_traits< DistanceMap >::value_type D;
+    typedef typename property_traits< WeightMap >::value_type W;
+    const D d_u = get(d, u);
+    const D d_v = get(d, v);
+    const W& w_e = get(w, e);
+
+    // The seemingly redundant comparisons after the distance puts are to
+    // ensure that extra floating-point precision in x87 registers does not
+    // lead to relax() returning true when the distance did not actually
+    // change.
+    if (compare(combine(d_u, w_e), d_v))
+    {
+        put(d, v, combine(d_u, w_e));
+        if (compare(get(d, v), d_v))
+        {
+            put(p, v, u);
+            return true;
+        }
+        else
+        {
+            return false;
+        }
+    }
+    else if (is_undirected && compare(combine(d_v, w_e), d_u))
+    {
+        put(d, u, combine(d_v, w_e));
+        if (compare(get(d, u), d_u))
+        {
+            put(p, u, v);
+            return true;
+        }
+        else
+        {
+            return false;
+        }
+    }
+    else
+        return false;
+}
+
+template < class Graph, class WeightMap, class PredecessorMap,
+    class DistanceMap, class BinaryFunction, class BinaryPredicate >
+bool relax_target(typename graph_traits< Graph >::edge_descriptor e,
+    const Graph& g, const WeightMap& w, PredecessorMap& p, DistanceMap& d,
+    const BinaryFunction& combine, const BinaryPredicate& compare)
+{
+    typedef typename graph_traits< Graph >::vertex_descriptor Vertex;
+    typedef typename property_traits< DistanceMap >::value_type D;
+    typedef typename property_traits< WeightMap >::value_type W;
+    const Vertex u = source(e, g);
+    const Vertex v = target(e, g);
+    const D d_u = get(d, u);
+    const D d_v = get(d, v);
+    const W& w_e = get(w, e);
+
+    // The seemingly redundant comparisons after the distance puts are to
+    // ensure that extra floating-point precision in x87 registers does not
+    // lead to relax() returning true when the distance did not actually
+    // change.
+    if (compare(combine(d_u, w_e), d_v))
+    {
+        put(d, v, combine(d_u, w_e));
+        if (compare(get(d, v), d_v))
+        {
+            put(p, v, u);
+            return true;
+        }
+    }
+    return false;
+}
+
+template < class Graph, class WeightMap, class PredecessorMap,
+    class DistanceMap >
+bool relax(typename graph_traits< Graph >::edge_descriptor e, const Graph& g,
+    WeightMap w, PredecessorMap p, DistanceMap d)
+{
+    typedef typename property_traits< DistanceMap >::value_type D;
+    typedef closed_plus< D > Combine;
+    typedef std::less< D > Compare;
+    return relax(e, g, w, p, d, Combine(), Compare());
+}
+
+} // namespace boost
+
+#endif /* BOOST_GRAPH_RELAX_HPP */