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