diff options
Diffstat (limited to 'src')
| -rw-r--r-- | src/Makefile.am | 1 | ||||
| -rw-r--r-- | src/blockfilter.cpp | 151 | ||||
| -rw-r--r-- | src/blockfilter.h | 5 |
3 files changed, 157 insertions, 0 deletions
diff --git a/src/Makefile.am b/src/Makefile.am index d8f8e57b4d..3701ee8f3c 100644 --- a/src/Makefile.am +++ b/src/Makefile.am @@ -220,6 +220,7 @@ libbitcoin_server_a_SOURCES = \ addrman.cpp \ bloom.cpp \ blockencodings.cpp \ + blockfilter.cpp \ chain.cpp \ checkpoints.cpp \ consensus/tx_verify.cpp \ diff --git a/src/blockfilter.cpp b/src/blockfilter.cpp new file mode 100644 index 0000000000..e4c95ccfbd --- /dev/null +++ b/src/blockfilter.cpp @@ -0,0 +1,151 @@ +// 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. + +#include <blockfilter.h> +#include <hash.h> +#include <streams.h> + +/// SerType used to serialize parameters in GCS filter encoding. +static constexpr int GCS_SER_TYPE = SER_NETWORK; + +/// Protocol version used to serialize parameters in GCS filter encoding. +static constexpr int GCS_SER_VERSION = 0; + +template <typename OStream> +static void GolombRiceEncode(BitStreamWriter<OStream>& bitwriter, uint8_t P, uint64_t x) +{ + // Write quotient as unary-encoded: q 1's followed by one 0. + uint64_t q = x >> P; + while (q > 0) { + int nbits = q <= 64 ? static_cast<int>(q) : 64; + bitwriter.Write(~0ULL, nbits); + q -= nbits; + } + bitwriter.Write(0, 1); + + // Write the remainder in P bits. Since the remainder is just the bottom + // P bits of x, there is no need to mask first. + bitwriter.Write(x, P); +} + +template <typename IStream> +static uint64_t GolombRiceDecode(BitStreamReader<IStream>& bitreader, uint8_t P) +{ + // Read unary-encoded quotient: q 1's followed by one 0. + uint64_t q = 0; + while (bitreader.Read(1) == 1) { + ++q; + } + + uint64_t r = bitreader.Read(P); + + return (q << P) + r; +} + +// Map a value x that is uniformly distributed in the range [0, 2^64) to a +// value uniformly distributed in [0, n) by returning the upper 64 bits of +// x * n. +// +// See: https://lemire.me/blog/2016/06/27/a-fast-alternative-to-the-modulo-reduction/ +static uint64_t MapIntoRange(uint64_t x, uint64_t n) +{ + // To perform the calculation on 64-bit numbers without losing the + // result to overflow, split the numbers into the most significant and + // least significant 32 bits and perform multiplication piece-wise. + // + // See: https://stackoverflow.com/a/26855440 + uint64_t x_hi = x >> 32; + uint64_t x_lo = x & 0xFFFFFFFF; + uint64_t n_hi = n >> 32; + uint64_t n_lo = n & 0xFFFFFFFF; + + uint64_t ac = x_hi * n_hi; + uint64_t ad = x_hi * n_lo; + uint64_t bc = x_lo * n_hi; + uint64_t bd = x_lo * n_lo; + + uint64_t mid34 = (bd >> 32) + (bc & 0xFFFFFFFF) + (ad & 0xFFFFFFFF); + uint64_t upper64 = ac + (bc >> 32) + (ad >> 32) + (mid34 >> 32); + return upper64; +} + +uint64_t GCSFilter::HashToRange(const Element& element) const +{ + uint64_t hash = CSipHasher(m_siphash_k0, m_siphash_k1) + .Write(element.data(), element.size()) + .Finalize(); + return MapIntoRange(hash, m_F); +} + +std::vector<uint64_t> GCSFilter::BuildHashedSet(const ElementSet& elements) const +{ + std::vector<uint64_t> hashed_elements; + hashed_elements.reserve(elements.size()); + for (const Element& element : elements) { + hashed_elements.push_back(HashToRange(element)); + } + std::sort(hashed_elements.begin(), hashed_elements.end()); + return hashed_elements; +} + +GCSFilter::GCSFilter(uint64_t siphash_k0, uint64_t siphash_k1, uint8_t P, uint32_t M) + : m_siphash_k0(siphash_k0), m_siphash_k1(siphash_k1), m_P(P), m_M(M), m_N(0), m_F(0) +{} + +GCSFilter::GCSFilter(uint64_t siphash_k0, uint64_t siphash_k1, uint8_t P, uint32_t M, + std::vector<unsigned char> encoded_filter) + : GCSFilter(siphash_k0, siphash_k1, P, M) +{ + m_encoded = std::move(encoded_filter); + + VectorReader stream(GCS_SER_TYPE, GCS_SER_VERSION, m_encoded, 0); + + uint64_t N = ReadCompactSize(stream); + m_N = static_cast<uint32_t>(N); + if (m_N != N) { + throw std::ios_base::failure("N must be <2^32"); + } + m_F = static_cast<uint64_t>(m_N) * static_cast<uint64_t>(m_M); + + // Verify that the encoded filter contains exactly N elements. If it has too much or too little + // data, a std::ios_base::failure exception will be raised. + BitStreamReader<VectorReader> bitreader(stream); + for (uint64_t i = 0; i < m_N; ++i) { + GolombRiceDecode(bitreader, m_P); + } + if (!stream.empty()) { + throw std::ios_base::failure("encoded_filter contains excess data"); + } +} + +GCSFilter::GCSFilter(uint64_t siphash_k0, uint64_t siphash_k1, uint8_t P, uint32_t M, + const ElementSet& elements) + : GCSFilter(siphash_k0, siphash_k1, P, M) +{ + size_t N = elements.size(); + m_N = static_cast<uint32_t>(N); + if (m_N != N) { + throw std::invalid_argument("N must be <2^32"); + } + m_F = static_cast<uint64_t>(m_N) * static_cast<uint64_t>(m_M); + + CVectorWriter stream(GCS_SER_TYPE, GCS_SER_VERSION, m_encoded, 0); + + WriteCompactSize(stream, m_N); + + if (elements.empty()) { + return; + } + + BitStreamWriter<CVectorWriter> bitwriter(stream); + + uint64_t last_value = 0; + for (uint64_t value : BuildHashedSet(elements)) { + uint64_t delta = value - last_value; + GolombRiceEncode(bitwriter, m_P, delta); + last_value = value; + } + + bitwriter.Flush(); +} diff --git a/src/blockfilter.h b/src/blockfilter.h index c0bd69b332..7809e6875a 100644 --- a/src/blockfilter.h +++ b/src/blockfilter.h @@ -31,6 +31,11 @@ private: 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. */ |