Add draft of Bloom filter type hierarchy.

src/BloomFilter.h

@@ -0,0 +1,266 @@
+#ifndef BloomFilter_h
+#define BloomFilter_h
+
+#include <vector>
+#include "BitVector.h"
+#include "Hash.h"
+#include "H3.h"
+
+/**
+ * A vector of counters, each of which have a fixed number of bits.
+ */
+class CounterVector : SerialObj {
+public:
+  /**
+   * Constructs a counter vector having cells of a given width.
+   *
+   * @param width The number of bits that each cell occupies.
+   */
+  explicit CounterVector(unsigned width);
+
+  /**
+   * Increments a given cell.
+   *
+   * @param cell The cell to increment.
+   *
+   * @param value The value to add to the current counter in *cell*.
+   *
+   * @return `true` if adding *value* to the counter in *cell* succeeded.
+   */
+  bool Increment(size_type cell, count_type value);
+
+  /**
+   * Decrements a given cell.
+   *
+   * @param cell The cell to decrement.
+   *
+   * @param value The value to subtract from the current counter in *cell*.
+   *
+   * @return `true` if subtracting *value* from the counter in *cell* succeeded.
+   */
+  bool Decrement(size_type cell, count_type value);
+
+  /**
+   * Retrieves the counter of a given cell.
+   *
+   * @param cell The cell index to retrieve the count for.
+   *
+   * @return The counter associated with *cell*.
+   */
+  count_type Count(size_type cell) const;
+
+  /**
+   * Retrieves the number of cells in the storage.
+   *
+   * @return The number of cells.
+   */
+  size_type Size() const;
+
+  bool Serialize(SerialInfo* info) const;
+  static CounterVector* Unserialize(UnserialInfo* info);
+
+protected:
+  DECLARE_SERIAL(CounterVector);
+
+  CounterVector();
+
+private:
+  BitVector bits_;
+  unsigned width_;
+};
+
+/**
+ * The abstract base class for hash policies.
+ * @tparam Codomain An integral type.
+ */
+class HashPolicy {
+public:
+  typedef hash_t hash_type;
+  virtual ~HashPolicy() { }
+  size_t k() const { return k; }
+  virtual std::vector<hash_type> Hash(const void* x, size_t n) const = 0;
+protected:
+  /**
+   * A functor that computes a universal hash function.
+   * @tparam Codomain An integral type.
+   */
+  template <typename Codomain = hash_type>
+  class Hasher {
+  public:
+    template <typename Domain>
+    Codomain operator()(const Domain& x) const
+      {
+      return h3_(&x, sizeof(x));
+      }
+    Codomain operator()(const void* x, size_t n) const
+      {
+      return h3_(x, n);
+      }
+  private:
+    // FIXME: The hardcoded value of 36 comes from UHASH_KEY_SIZE defined in
+    // Hash.h. I do not know how this value impacts the hash function behavior
+    // so I'll just copy it verbatim. (Matthias)
+    H3<Codomain, 36> h3_;
+  };
+
+  HashPolicy(size_t k) : k_(k) { }
+private:
+  size_t k_;
+};
+
+/**
+ * The *default* hashing policy. Performs *k* hash function computations.
+ */
+class DefaultHashing : public HashPolicy {
+public:
+  DefaultHashing(size_t k) : HashPolicy(k), hashers_(k) { }
+  virtual ~DoubleHashing() { }
+
+  virtual std::vector<hash_type> Hash(const void* x, size_t n) const
+    {
+    std::vector<hash_type> h(k(), 0);
+    for (size_t i = 0; i < h.size(); ++i)
+      h[i] = hashers_[i](x, n);
+    return h;
+    }
+
+private:
+  std::vector< Hasher<hash_type> > hashers_;
+};
+
+/**
+ * The *double-hashing* policy. Uses a linear combination of 2 hash functions.
+ */
+class DoubleHashing : public HashPolicy {
+public:
+  DoubleHashing(size_t k) : HashPolicy(k), hashers_(k) { }
+  virtual ~DoubleHashing() { }
+
+  virtual std::vector<hash_type> Hash(const void* x, size_t n) const
+    {
+    Codomain h1 = hasher1_(x);
+    Codomain h2 = hasher2_(x);
+    std::vector<hash_type> h(k(), 0);
+    for (size_t i = 0; i < h.size(); ++i)
+      h[i] = h1 + i * h2;
+    return h;
+    }
+
+private:
+  Hasher<hash_type> hasher1_;
+  Hasher<hash_type> hasher2_;
+};
+
+/**
+ * The abstract base class for Bloom filters.
+ */
+class BloomFilter : SerialObj {
+public:
+  virtual ~BloomFilter() { delete hash_; }
+
+  /**
+   * Adds an element of type T to the Bloom filter.
+   * @param x The element to add
+   */
+  template <typename T>
+  void Add(const T& x)
+    {
+    ++elements_;
+    AddImpl(hash_->Hash(x));
+    }
+
+  /**
+   * Retrieves the associated count of a given value.
+   *
+   * @param x The value of type `T` to check.
+   *
+   * @return The counter associated with *x*.
+   */
+  template <typename T>
+  size_t Count(const T& x) const
+    {
+    return CountImpl(hash_->Hash(x));
+    }
+
+  /**
+   * Retrieves the number of elements added to the Bloom filter.
+   *
+   * @return The number of elements in this Bloom filter.
+   */
+  size_t Size() const
+    {
+    return elements_;
+    }
+
+protected:
+  typedef std::vector<HashPolicy::hash_value> HashVector;
+
+  /**
+   * Default-constructs a Bloom filter.
+   */
+	BloomFilter();
+
+  /**
+   * Constructs a BloomFilter.
+   * @param hash The hashing policy.
+   */
+  BloomFilter(HashPolicy* hash);
+
+  virtual void AddImpl(const HashVector& hashes) = 0;
+
+  virtual size_t CountImpl(const HashVector& hashes) const = 0;
+
+  std::vector<HashPolicy::hash_value> Hash(const T& x) const
+    {
+    return hash_->Hash(&x, sizeof(x));
+    }
+
+private:
+  HashPolicy<T>* hash_;  // Owned by *this.
+
+  size_t elements_;
+};
+
+/**
+ * A basic Bloom filter.
+ */
+class BasicBloomFilter : public BloomFilter {
+public:
+  BasicBloomFilter();
+  BasicBloomFilter(HashPolicy* hash);
+
+protected:
+  virtual void AddImpl(const HashVector& h)
+    {
+    for ( size_t i = 0; i < h.size(); ++i )
+      bits_.set(h[i] % h.size());
+    }
+
+  virtual size_t CountImpl(const HashVector& h) const
+    {
+    for ( size_t i = 0; i < h.size(); ++i )
+      if ( ! bits_[h[i] % h.size()] )
+        return 0;
+    return 1;
+    }
+
+private:
+  BitVector bits_;
+};
+
+/**
+ * A counting Bloom filter.
+ */
+class CountingBloomFilter : public BloomFilter {
+public:
+  CountingBloomFilter(unsigned width);
+  CountingBloomFilter(HashPolicy* hash);
+
+protected:
+  CountingBloomFilter();
+
+private:
+  CounterVector cells_;
+};
+
+#endif

src/CMakeLists.txt

@@ -304,6 +304,7 @@ set(bro_SRCS
     BitTorrent.cc
     BitTorrentTracker.cc
     BitVector.cc
+    BloomFilter.cc
     BPF_Program.cc
     BroDoc.cc
     BroDocObj.cc