More indeterminism fixes

Author: chschulte

changelog.in

@@ -81,6 +81,18 @@ using memory addresses for determining the order of variables in
 some propagators which in turn affected which propagator might
 record failure first and hence influenced the branching decisions.
 
+[ENTRY]
+Module: int
+What:   bug
+Rank:   major
+[DESCRIPTION]
+For the combination of binpacking and linear constraints with
+shared variable selection branching (that is, AFC, Action, and
+CHB) the behavior of Gecode was indeterminstic. The indeterminism
+was based on using memory addresses for determining the order of
+variables which in turn affected which propagator might record
+failure first and hence influenced the branching decisions.
+
 [ENTRY]
 Module: example
 What:   new

gecode/int/bin-packing/propagate.hpp

@@ -80,8 +80,7 @@ namespace Gecode { namespace Int { namespace BinPacking {
   /// For sorting according to size
   forceinline bool
   operator <(const Item& i, const Item& j) {
-    return ((i.size() > j.size()) ||
-            ((i.size() == j.size()) && (i.bin() < j.bin())));
+    return i.size() > j.size();
   }
 
 

gecode/int/linear.hh

@@ -1339,6 +1339,8 @@ namespace Gecode { namespace Int { namespace Linear {
     int a;
     /// View
     View x;
+    /// Original position in array (for sorting into canonical order)
+    int p;
   };
 
   /** \brief Estimate lower and upper bounds

gecode/int/linear/post.hpp

@@ -65,14 +65,25 @@ namespace Gecode { namespace Int { namespace Linear {
 
   /// Sort linear terms by view
   template<class View>
-  class TermLess {
+  class TermByView {
   public:
     forceinline bool
     operator ()(const Term<View>& a, const Term<View>& b) {
       return a.x < b.x;
     }
   };
 
+  /// Sort linear terms by coefficient size and original position
+  template<class View>
+  class TermBySizePos {
+  public:
+    forceinline bool
+    operator ()(const Term<View>& a, const Term<View>& b) {
+      assert((a.a > 0) && (b.a > 0));
+      return (a.a > b.a) || ((a.a == b.a) && (a.p < b.p));
+    }
+  };
+
   /// Compute the greatest common divisor of \a a and \a b
   inline int
   gcd(int a, int b) {
@@ -116,28 +127,34 @@ namespace Gecode { namespace Int { namespace Linear {
             Term<View>* &t_p, int &n_p,
             Term<View>* &t_n, int &n_n,
             int& g) {
+    // Number terms by position
+    for (int i=0; i<n; i++)
+      t[i].p = i;
+
     /*
      * Join coefficients for aliased variables:
      *
      */
     {
       // Group same variables
-      TermLess<View> tl;
-      Support::quicksort<Term<View>,TermLess<View> >(t,n,tl);
+      TermByView<View> tl;
+      Support::quicksort<Term<View>,TermByView<View>>(t,n,tl);
 
       // Join adjacent variables
       int i = 0;
       int j = 0;
       while (i < n) {
         Limits::check(t[i].a,"Int::linear");
         long long int a = t[i].a;
+        int p = t[i].p;
         View x = t[i].x;
         while ((++i < n) && (t[i].x == x)) {
           a += t[i].a;
+          p = std::min(p,t[i].p);
           Limits::check(a,"Int::linear");
         }
         if (a != 0) {
-          t[j].a = static_cast<int>(a); t[j].x = x; j++;
+          t[j].a = static_cast<int>(a); t[j].x = x; t[j].p = p; j++;
         }
       }
       n = j;
@@ -170,6 +187,15 @@ namespace Gecode { namespace Int { namespace Linear {
     for (int i=0; i<n_n; i++)
       t_n[i].a = -t_n[i].a;
 
+    /*
+     * Sort terms into canonical order (to avoid indeterminstic order)
+     */
+    {
+      TermBySizePos<View> tl;
+      Support::quicksort<Term<View>,TermBySizePos<View>>(t_p,n_p,tl);
+      Support::quicksort<Term<View>,TermBySizePos<View>>(t_n,n_n,tl);
+    }
+    
     /*
      * Compute greatest common divisor
      *