blockfilter: Declare GCSFilter class for BIP 158 impl.

Author: Jim Posen

src/Makefile.am

@@ -96,6 +96,7 @@ BITCOIN_CORE_H = \
   bech32.h \
   bloom.h \
   blockencodings.h \
+  blockfilter.h \
   chain.h \
   chainparams.h \
   chainparamsbase.h \

src/blockfilter.h

@@ -0,0 +1,66 @@
+// 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;
+
+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