Update sat_ddfw.h

Author: NikolajBjorner

src/ast/sls/sat_ddfw.h

@@ -72,6 +72,7 @@ namespace sat {
             double   m_reward = 0;
             double   m_last_reward = 0;
             unsigned m_make_count = 0;
+            unsigned m_timestamp = 0;
             int      m_bias = 0;
             ema      m_reward_avg = 1e-5;
         };
@@ -283,6 +284,8 @@ namespace sat {
 
         inline int& bias(bool_var v) { return m_vars[v].m_bias; }
 
+        unsigned timestamp(bool_var v) { return m_vars[v].m_timestamp; }
+
         void reserve_vars(unsigned n);
 
         void add(unsigned sz, literal const* c);