Support emptiness check on Bloom filters.

src/OpaqueVal.cc

@@ -583,6 +583,11 @@ void BloomFilterVal::Clear()
 	bloom_filter->Clear();
 	}
 
+bool BloomFilterVal::Empty() const
+	{
+	return bloom_filter->Empty();
+	}
+
 BloomFilterVal* BloomFilterVal::Merge(const BloomFilterVal* x,
 		const BloomFilterVal* y)
 	{

src/OpaqueVal.h

@@ -126,6 +126,7 @@ public:
 	void Add(const Val* val);
 	size_t Count(const Val* val) const;
 	void Clear();
+	bool Empty() const;
 
 	static BloomFilterVal* Merge(const BloomFilterVal* x,
 				     const BloomFilterVal* y);

src/probabilistic/BitVector.cc

@@ -463,6 +463,14 @@ bool BitVector::Empty() const
 	return bits.empty();
 	}
 
+bool BitVector::AllZero() const
+	{
+	for ( size_t i = 0; i < bits.size(); ++i )
+		if ( bits[i] )
+			return false;
+	return true;
+	}
+
 BitVector::size_type BitVector::FindFirst() const
 	{
 	return find_from(0);

src/probabilistic/BitVector.h

@@ -253,6 +253,12 @@ public:
 	 */
 	bool Empty() const;
 
+	/**
+	 * Checks whether all bits are 0.
+	 * @return `true` iff all bits in all blocks are 0.
+	 */
+	bool AllZero() const;
+
 	/**
 	 * Finds the bit position of of the first 1-bit.
 	 * @return The position of the first bit that equals to one or `npos` if no

src/probabilistic/BloomFilter.cc

@@ -74,6 +74,11 @@ size_t BasicBloomFilter::K(size_t cells, size_t capacity)
 	return std::ceil(frac * std::log(2));
 	}
 
+bool BasicBloomFilter::Empty() const
+	{
+	return bits->AllZero();
+	}
+
 void BasicBloomFilter::Clear()
 	{
 	bits->Clear();
@@ -167,6 +172,11 @@ CountingBloomFilter::CountingBloomFilter(const Hasher* hasher,
 	cells = new CounterVector(width, arg_cells);
 	}
 
+bool CountingBloomFilter::Empty() const
+	{
+	return cells->AllZero();
+	}
+
 void CountingBloomFilter::Clear()
 	{
 	cells->Clear();

src/probabilistic/BloomFilter.h

@@ -47,6 +47,13 @@ public:
 		return CountImpl((*hasher)(x));
 		}
 
+	/**
+	 * Checks whether the Bloom filter is empty.
+	 *
+	 * @return `true` if the Bloom filter contains no elements.
+	 */
+	virtual bool Empty() const = 0;
+
 	/**
 	 * Removes all elements, i.e., resets all bits in the underlying bit vector.
 	 */
@@ -169,6 +176,7 @@ public:
 	static size_t K(size_t cells, size_t capacity);
 
 	// Overridden from BloomFilter.
+	virtual bool Empty() const;
 	virtual void Clear();
 	virtual bool Merge(const BloomFilter* other);
 	virtual BasicBloomFilter* Clone() const;
@@ -207,6 +215,7 @@ public:
 	CountingBloomFilter(const Hasher* hasher, size_t cells, size_t width);
 
 	// Overridden from BloomFilter.
+	virtual bool Empty() const;
 	virtual void Clear();
 	virtual bool Merge(const BloomFilter* other);
 	virtual CountingBloomFilter* Clone() const;

src/probabilistic/CounterVector.cc

@@ -70,6 +70,11 @@ bool CounterVector::Decrement(size_type cell, count_type value)
 	return carry;
 	}
 
+bool CounterVector::AllZero() const
+	{
+	return bits->AllZero();
+	}
+
 void CounterVector::Clear()
 	{
 	bits->Clear();

src/probabilistic/CounterVector.h

@@ -77,6 +77,12 @@ public:
 	 */
 	count_type Count(size_type cell) const;
 
+	/**
+	 * Checks whether all counters are 0.
+	 * @return `true` iff all counters have the value 0.
+	 */
+	bool AllZero() const;
+
 	/**
 	 * Sets all counters to 0.
 	 */

src/probabilistic/bloom-filter.bif

@@ -109,6 +109,9 @@ function bloomfilter_lookup%(bf: opaque of bloomfilter, x: any%): count
 	%{
 	const BloomFilterVal* bfv = static_cast<const BloomFilterVal*>(bf);
 
+	if ( bfv->Empty() )
+		return new Val(0, TYPE_COUNT);
+
 	if ( ! bfv->Type() )
 		reporter->Error("cannot perform lookup on untyped Bloom filter");