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// Copyright (c) 2018 The Bitcoin Core developers
// Distributed under the MIT software license, see the accompanying
// file COPYING or http://www.opensource.org/licenses/mit-license.php.
#ifndef BITCOIN_BLOCKFILTER_H
#define BITCOIN_BLOCKFILTER_H
#include <set>
#include <stdint.h>
#include <vector>
#include <serialize.h>
#include <uint256.h>
/**
* This implements a Golomb-coded set as defined in BIP 158. It is a
* compact, probabilistic data structure for testing set membership.
*/
class GCSFilter
{
public:
typedef std::vector<unsigned char> Element;
typedef std::set<Element> ElementSet;
private:
uint64_t m_siphash_k0;
uint64_t m_siphash_k1;
uint8_t m_P; //!< Golomb-Rice coding parameter
uint32_t m_M; //!< Inverse false positive rate
uint32_t m_N; //!< Number of elements in the filter
uint64_t m_F; //!< Range of element hashes, F = N * M
std::vector<unsigned char> m_encoded;
/** Hash a data element to an integer in the range [0, N * M). */
uint64_t HashToRange(const Element& element) const;
std::vector<uint64_t> BuildHashedSet(const ElementSet& elements) const;
public:
/** Constructs an empty filter. */
GCSFilter(uint64_t siphash_k0 = 0, uint64_t siphash_k1 = 0, uint8_t P = 0, uint32_t M = 0);
/** Reconstructs an already-created filter from an encoding. */
GCSFilter(uint64_t siphash_k0, uint64_t siphash_k1, uint8_t P, uint32_t M,
std::vector<unsigned char> encoded_filter);
/** Builds a new filter from the params and set of elements. */
GCSFilter(uint64_t siphash_k0, uint64_t siphash_k1, uint8_t P, uint32_t M,
const ElementSet& elements);
uint8_t GetP() const { return m_P; }
uint32_t GetN() const { return m_N; }
uint32_t GetM() const { return m_M; }
const std::vector<unsigned char>& GetEncoded() const { return m_encoded; }
/**
* Checks if the element may be in the set. False positives are possible
* with probability 1/M.
*/
bool Match(const Element& element) const;
/**
* Checks if any of the given elements may be in the set. False positives
* are possible with probability 1/M per element checked. This is more
* efficient that checking Match on multiple elements separately.
*/
bool MatchAny(const ElementSet& elements) const;
};
#endif // BITCOIN_BLOCKFILTER_H
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