text: // Copyright (c) 2012-2020 The shitecoin Core developers
  // Distributed under the MIT software license, see the accompanying
  // file COPYING or http://www.opensource.org/licenses/mit-license.php.
  
  #ifndef shitecoin_BLOOM_H
  #define shitecoin_BLOOM_H
  
  #include <serialize.h>
  
  #include <vector>
  
  class COutPoint;
  class CTransaction;
  class uint256;
  
  //! 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 send them.
   *
   * This allows for significantly more efficient transaction and block downloads.
   *
   * Because bloom filters are probabilistic, a SPV node can increase the false-
   * positive rate, making us send it transactions which aren't actually its,
   * allowing clients to trade more bandwidth for more privacy by obfuscating which
   * keys are controlled by them.
   */
  class CBloomFilter
  {
  private:
      std::vector<unsigned char> vData;
      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(const unsigned int nElements, const double nFPRate, const unsigned int nTweak, unsigned char nFlagsIn);
      CBloomFilter() : nHashFuncs(0), nTweak(0), nFlags(0) {}
  
      SERIALIZE_METHODS(CBloomFilter, obj) { READWRITE(obj.vData, obj.nHashFuncs, obj.nTweak, obj.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);
  };
  
  /**
   * RollingBloomFilter is a probabilistic "keep track of most recently inserted" set.
   * Construct it with the number of items to keep track of, and a false-positive
   * rate. Unlike CBloomFilter, by default nTweak is set to a cryptographically
   * secure random value for you. Similarly rather than clear() the method
   * reset() is provided, which also changes nTweak to decrease the impact of
   * false-positives.
   *
   * contains(item) will always return true if item was one of the last N to 1.5*N
   * insert()'ed ... but may also return true for items that were not inserted.
   *
   * It needs around 1.8 bytes per element per factor 0.1 of false positive rate.
   * For example, if we want 1000 elements, we'd need:
   * - ~1800 bytes for a false positive rate of 0.1
   * - ~3600 bytes for a false positive rate of 0.01
   * - ~5400 bytes for a false positive rate of 0.001
   *
   * If we make these simplifying assumptions:
   * - logFpRate / log(0.5) doesn't get rounded or clamped in the nHashFuncs calculation
   * - nElements is even, so that nEntriesPerGeneration == nElements / 2
   *
   * Then we get a more accurate estimate for filter bytes:
   *
   *     3/(log(256)*log(2)) * log(1/fpRate) * nElements
   */
  class CRollingBloomFilter
  {
  public:
      CRollingBloomFilter(const unsigned int nElements, const double nFPRate);
  
      void insert(const std::vector<unsigned char>& vKey);
      void insert(const uint256& hash);
      bool contains(const std::vector<unsigned char>& vKey) const;
      bool contains(const uint256& hash) const;
  
      void reset();
  
  private:
      int nEntriesPerGeneration;
      int nEntriesThisGeneration;
      int nGeneration;
      std::vector<uint64_t> data;
      unsigned int nTweak;
      int nHashFuncs;
  };
  
  #endif // shitecoin_BLOOM_H
  