136 lines
4.3 KiB
C++
136 lines
4.3 KiB
C++
//=======================================================================
|
|
// 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 */
|