[dasher: 2/5] Robustness improvements to ExpansionPolicy code for finding-next-smallest double

[Patrick Welche <pwelche src gnome org>]

commit 05f3660e3b6945003b106d48c43c93e5f2909461
Author: Alan Lawrence <acl33 inf phy cam ac uk>
Date:   Sat Dec 19 21:01:21 2009 +0000

    Robustness improvements to ExpansionPolicy code for finding-next-smallest double

 Src/DasherCore/ExpansionPolicy.cpp |   10 +++++++---
 1 files changed, 7 insertions(+), 3 deletions(-)
---
diff --git a/Src/DasherCore/ExpansionPolicy.cpp b/Src/DasherCore/ExpansionPolicy.cpp
index 62b8a1d..15e8ffc 100644
--- a/Src/DasherCore/ExpansionPolicy.cpp
+++ b/Src/DasherCore/ExpansionPolicy.cpp
@@ -22,10 +22,14 @@ BudgettingPolicy::BudgettingPolicy(unsigned int iNodeBudget) : m_iNodeBudget(iNo
 double BudgettingPolicy::pushNode(CDasherNode *pNode, int iMin, int iMax, bool bExpand, double dParentCost) {
   double dRes = getCost(pNode, iMin, iMax);
   if (dRes >= dParentCost) {
-    double eps = min(1.0, abs(dParentCost));
-    while (dParentCost - (eps/2.0) < dParentCost) eps/=2.0;
-    dRes = dParentCost - eps;
+    double eps = max(abs(dParentCost),1.0) * std::numeric_limits<double>::epsilon();
+    DASHER_ASSERT((dParentCost-eps) < dParentCost);
+    for (double nRes; (nRes = dParentCost - eps) < dParentCost; eps/=2.0) {
+      //nRes<dParentCost guaranteed true by loop test - remember it!
+      dRes = nRes;
+    }
   }
+  DASHER_ASSERT(dRes < dParentCost);
   vector<pair<double, CDasherNode*> > &target = (bExpand) ? sExpand : sCollapse;
   target.push_back(pair<double, CDasherNode *>(dRes,pNode));
   return dRes;