/**
* Constructs a proof finder for the given log.
*
* @ensures this.log' = log
*/
NodePruner(TranslationLog log) {
visited = new IdentityHashSet<Node>();
relevant = new IdentityHashSet<Node>();
final RecordFilter filter =
new RecordFilter() {
public boolean accept(
Node node, Formula translated, int literal, Map<Variable, TupleSet> env) {
return env.isEmpty();
}
};
constNodes = new LinkedHashMap<Formula, Boolean>();
for (Iterator<TranslationRecord> itr = log.replay(filter); itr.hasNext(); ) {
TranslationRecord rec = itr.next();
int lit = rec.literal();
if (Math.abs(lit) != Integer.MAX_VALUE) {
constNodes.remove(rec.translated());
} else if (lit == Integer.MAX_VALUE) {
constNodes.put(rec.translated(), Boolean.TRUE);
} else {
constNodes.put(rec.translated(), Boolean.FALSE);
}
}
}
/**
* {@inheritDoc}
*
* @see kodkod.engine.Proof#highLevelCore()
*/
public final Map<Formula, Node> highLevelCore() {
if (coreRoots == null) {
final Iterator<TranslationRecord> itr = core();
final Set<Formula> roots = log().roots();
coreRoots = new LinkedHashMap<Formula, Node>();
while (itr.hasNext()) {
TranslationRecord rec = itr.next();
if (roots.contains(rec.translated())) coreRoots.put(rec.translated(), rec.node());
}
coreRoots = Collections.unmodifiableMap(coreRoots);
}
return coreRoots;
}
/**
* Minimizes the current core using the trivial strategy that does one of the following: (1) if
* there is a root that simplified to FALSE, sets the minimal core to that root; or (2) if not,
* there must be two roots that translated to x and -x, where x is a boolean literal, so we pick
* those two as the minimal core. The strategy argument is ignored (it can be null).
*
* @see Proof#minimize(ReductionStrategy)
*/
@Override
public void minimize(ReductionStrategy strategy) {
final Map<Formula, int[]> rootLits = new LinkedHashMap<Formula, int[]>();
final Map<Formula, Node> rootNodes = new LinkedHashMap<Formula, Node>();
final Set<Formula> roots = log().roots();
for (Iterator<TranslationRecord> itr = core(); itr.hasNext(); ) {
final TranslationRecord rec = itr.next();
if (roots.contains(rec.translated())) {
// simply record the most recent output value for each formula:
// this is guaranteed to be the final output value for that
// formula because of the translation log guarantee that the
// log is replayed in the order of translation: i.e. a child's
// output value is always recorded before the parent's
int[] val = rootLits.get(rec.translated());
if (val == null) {
val = new int[1];
rootLits.put(rec.translated(), val);
}
val[0] = rec.literal();
rootNodes.put(rec.translated(), rec.node());
}
}
final SparseSequence<Formula> lits = new TreeSequence<Formula>();
for (Map.Entry<Formula, int[]> entry : rootLits.entrySet()) {
final int lit = entry.getValue()[0];
if (lit == -Integer.MAX_VALUE) {
coreRoots = Collections.singletonMap(entry.getKey(), rootNodes.get(entry.getKey()));
break;
} else if (lits.containsIndex(-lit)) {
final Formula f0 = lits.get(-lit);
final Formula f1 = entry.getKey();
coreRoots = new LinkedHashMap<Formula, Node>(3);
coreRoots.put(f0, rootNodes.get(f0));
coreRoots.put(f1, rootNodes.get(f1));
coreRoots = Collections.unmodifiableMap(coreRoots);
break;
} else {
lits.put(lit, entry.getKey());
}
}
coreFilter = null;
assert coreRoots.size() == 1
&& rootLits.get(coreRoots.keySet().iterator().next())[0] == -Integer.MAX_VALUE
|| coreRoots.size() == 2;
}