/// searchForAssignment - Look for a cached solution for a query.
///
/// \param key - The query to look up.
/// \param result [out] - The cached result, if the lookup is succesful. This is
/// either a satisfying assignment (for a satisfiable query), or 0 (for an
/// unsatisfiable query).
/// \return - True if a cached result was found.
bool CexCachingSolver::searchForAssignment(KeyType &key, Assignment *&result) {
AssignmentCacheWrapper * const *lookup = cache.lookup(key);
if (lookup) {
result = (*lookup)->getAssignment();
unsatCore = (*lookup)->getCore();
return true;
}
if (CexCacheTryAll) {
// Look for a satisfying assignment for a superset, which is trivially an
// assignment for any subset.
AssignmentCacheWrapper **lookup = 0;
if (CexCacheSuperSet)
lookup = cache.findSuperset(key, NonNullAssignment());
// Otherwise, look for a subset which is unsatisfiable, see below.
if (!lookup)
lookup = cache.findSubset(key, NullAssignment());
// If either lookup succeeded, then we have a cached solution.
if (lookup) {
result = (*lookup)->getAssignment();
unsatCore = (*lookup)->getCore();
return true;
}
// Otherwise, iterate through the set of current assignments to see if one
// of them satisfies the query.
for (assignmentsTable_ty::iterator it = assignmentsTable.begin(),
ie = assignmentsTable.end(); it != ie; ++it) {
Assignment *a = *it;
if (a->satisfies(key.begin(), key.end())) {
result = a;
unsatCore.clear();
return true;
}
}
} else {
// FIXME: Which order? one is sure to be better.
// Look for a satisfying assignment for a superset, which is trivially an
// assignment for any subset.
AssignmentCacheWrapper **lookup = 0;
if (CexCacheSuperSet)
lookup = cache.findSuperset(key, NonNullAssignment());
// Otherwise, look for a subset which is unsatisfiable -- if the subset is
// unsatisfiable then no additional constraints can produce a valid
// assignment. While searching subsets, we also explicitly the solutions for
// satisfiable subsets to see if they solve the current query and return
// them if so. This is cheap and frequently succeeds.
if (!lookup)
lookup = cache.findSubset(key, NullOrSatisfyingAssignment(key));
// If either lookup succeeded, then we have a cached solution.
if (lookup) {
result = (*lookup)->getAssignment();
unsatCore = (*lookup)->getCore();
return true;
}
}
return false;
}
