text: // Copyright (c) 2012 The Om developers
  // Distributed under the MIT/X11 software license, see the accompanying
  // file COPYING or http://www.opensource.org/licenses/mit-license.php.
  #ifndef BITCOIN_BLOOM_H
  #define BITCOIN_BLOOM_H
  
  #include <vector>
  
  #include "uint256.h"
  #include "serialize.h"
  
  class COutPoint;
  class CTransaction;
  
  // 20,000 items with fp rate < 0.1% or 10,000 items and <0.0001%
  static const unsigned int MAX_BLOOM_FILTER_SIZE = 36000; // bytes
  static const unsigned int MAX_HASH_FUNCS = 50;
  
  // First two bits of nFlags control how much IsRelevantAndUpdate actually updates
  // The remaining bits are reserved
  enum bloomflags
  {
      BLOOM_UPDATE_NONE = 0,
      BLOOM_UPDATE_ALL = 1,
      // Only adds outpoints to the filter if the output is a pay-to-pubkey/pay-to-multisig script
      BLOOM_UPDATE_P2PUBKEY_ONLY = 2,
      BLOOM_UPDATE_MASK = 3,
  };
  
  /**
   * BloomFilter is a probabilistic filter which SPV clients provide
   * so that we can filter the transactions we sends them.
   * 
   * This allows for significantly more efficient transaction and block downloads.
   * 
   * Because bloom filters are probabilistic, an SPV node can increase the false-
   * positive rate, making us send them transactions which aren't actually theirs, 
   * allowing clients to trade more bandwidth for more privacy by obfuscating which
   * keys are owned by them.
   */
  class CBloomFilter
  {
  private:
      std::vector<unsigned char> vData;
      bool isFull;
      bool isEmpty;
      unsigned int nHashFuncs;
      unsigned int nTweak;
      unsigned char nFlags;
  
      unsigned int Hash(unsigned int nHashNum, const std::vector<unsigned char>& vDataToHash) const;
  
  public:
      // Creates a new bloom filter which will provide the given fp rate when filled with the given number of elements
      // Note that if the given parameters will result in a filter outside the bounds of the protocol limits,
      // the filter created will be as close to the given parameters as possible within the protocol limits.
      // This will apply if nFPRate is very low or nElements is unreasonably high.
      // nTweak is a constant which is added to the seed value passed to the hash function
      // It should generally always be a random value (and is largely only exposed for unit testing)
      // nFlags should be one of the BLOOM_UPDATE_* enums (not _MASK)
      CBloomFilter(unsigned int nElements, double nFPRate, unsigned int nTweak, unsigned char nFlagsIn);
      CBloomFilter() : isFull(true) {}
  
      IMPLEMENT_SERIALIZE
      (
          READWRITE(vData);
          READWRITE(nHashFuncs);
          READWRITE(nTweak);
          READWRITE(nFlags);
      )
  
      void insert(const std::vector<unsigned char>& vKey);
      void insert(const COutPoint& outpoint);
      void insert(const uint256& hash);
  
      bool contains(const std::vector<unsigned char>& vKey) const;
      bool contains(const COutPoint& outpoint) const;
      bool contains(const uint256& hash) const;
  
      // True if the size is <= MAX_BLOOM_FILTER_SIZE and the number of hash functions is <= MAX_HASH_FUNCS
      // (catch a filter which was just deserialized which was too big)
      bool IsWithinSizeConstraints() const;
  
      // Also adds any outputs which match the filter to the filter (to match their spending txes)
      bool IsRelevantAndUpdate(const CTransaction& tx, const uint256& hash);
  
      // Checks for empty and full filters to avoid wasting cpu
      void UpdateEmptyFull();
  };
  
  #endif /* BITCOIN_BLOOM_H */
  