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added closed plus

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[SVN r11005]
This commit is contained in:
Jeremy Siek
2001-09-03 20:36:22 +00:00
parent 8e55436641
commit 020fff0e68
1 changed files with 14 additions and 10 deletions
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24
include/boost/graph/relax.hpp
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@@ -41,11 +41,19 @@ namespace std { using ::abs; }
namespace boost {
// warning: when weight of e is size_t and weight of e is
// close to max of size_t, du + wuv will overflow. To avoid
// this, be careful about the value of weight. If it is larger
// than the half of current max of the type, change the type of
// weight to have more bytes.
// The following version of the plus functor prevents
// problems due to overflow at positive infinity.
template <class T>
struct closed_plus
{
T operator()(const T& a, const T& b) const {
T inf = std::numeric_limits<T>::max();
if (b > 0 && std::abs(inf - a) < b)
return inf;
return a + b;
}
};
template <class Graph, class WeightMap,
class PredecessorMap, class DistanceMap,
@@ -61,10 +69,6 @@ namespace boost {
typedef typename property_traits<WeightMap>::value_type W;
D d_u = get(d, u), d_v = get(d, v);
W w_e = get(w, e);
// workaround overflow problem, don't relax if d_u is close to inf
if (w_e > 0 && std::abs(std::numeric_limits<D>::max() - d_u) < w_e)
return false;
if ( compare(combine(d_u, w_e), d_v) ) {
put(d, v, combine(d_u, w_e));
@@ -80,7 +84,7 @@ namespace boost {
const Graph& g, WeightMap w, PredecessorMap p, DistanceMap d)
{
typedef typename property_traits<DistanceMap>::value_type D;
typedef std::plus<D> Combine;
typedef closed_plus<D> Combine;
typedef std::less<D> Compare;
return relax(e, g, w, p, d, Combine(), Compare());
}