Fix handling of overflow in shortest-path algorithms

[SVN r37814]

doc/history.html

@@ -76,6 +76,10 @@ September 27, 2000.
 <h2>Changes by version</h2>
 <a name="by-version">
 <ul>
+  <a name="1.34.1"></a><li>Version 1.34.1</br><b>Bug Fixes</b><br>
+  <ul>
+     <li><a href="bellman_ford_shortest.html"><tt>bellman_ford_shortest_paths</tt></a>: fixed a bug where certain negative cycles were not correctly detected.</li>
+  </ul>
   <a name="1.34.0"></a><li>Version 1.34.0<br><b>New algorithms and components</b>
     <ul>
       <li><a href="maximum_matching.html"><tt>edmonds_maximum_cardinality_matching</tt></a>, from Aaron Windsor.</li>

include/boost/graph/relax.hpp

@@ -22,16 +22,13 @@ namespace boost {
     template <class T>
     struct closed_plus
     {
-      // std::abs just isn't portable :(
-      template <class X>
-      inline X my_abs(const X& x) const { return x < 0 ? -x : x; }
-
       T operator()(const T& a, const T& b) const {
         using namespace std;
-        T inf = (numeric_limits<T>::max)();
-        if (b > 0 && my_abs(inf - a) < b)
-          return inf;
-        return a + b;
+	T zero(0);
+	T result = a + b;
+	if (result < zero && a >= zero && b >= zero)
+	  return (numeric_limits<T>::max)();
+	return result;
       }
     };