e928bcaf19
Like boost::dynamic_bitset, but less capable. On the other hand it avoids very large allocations, which are incurred by the bloom filter's bitset on even moderately sized sstables.
62 lines
1.8 KiB
C++
62 lines
1.8 KiB
C++
/*
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* Copyright (C) 2015 Cloudius Systems, Ltd.
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*/
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// A bitset containing a very large number of bits, so it uses fragmented
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// storage in order not to stress the memory allocator.
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#pragma once
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#include <memory>
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#include <vector>
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#include <limits>
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class large_bitset {
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static constexpr size_t block_size() { return 128 * 1024; }
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using int_type = unsigned long;
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static constexpr size_t bits_per_int() {
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return std::numeric_limits<int_type>::digits;
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}
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static constexpr size_t ints_per_block() {
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return block_size() / sizeof(int_type);
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}
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static constexpr size_t bits_per_block() {
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return ints_per_block() * bits_per_int();
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}
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size_t _nr_bits = 0;
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std::vector<std::unique_ptr<int_type[]>> _storage;
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public:
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explicit large_bitset(size_t nr_bits);
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large_bitset(large_bitset&&) = default;
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large_bitset(const large_bitset&) = delete;
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large_bitset& operator=(const large_bitset&) = delete;
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size_t size() const {
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return _nr_bits;
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}
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bool test(size_t idx) const {
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auto idx1 = idx / bits_per_block();
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idx %= bits_per_block();
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auto idx2 = idx / bits_per_int();
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idx %= bits_per_int();
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auto idx3 = idx;
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return (_storage[idx1][idx2] >> idx3) & 1;
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}
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void set(size_t idx) {
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auto idx1 = idx / bits_per_block();
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idx %= bits_per_block();
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auto idx2 = idx / bits_per_int();
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idx %= bits_per_int();
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auto idx3 = idx;
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_storage[idx1][idx2] |= int_type(1) << idx3;
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}
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void clear(size_t idx) {
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auto idx1 = idx / bits_per_block();
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idx %= bits_per_block();
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auto idx2 = idx / bits_per_int();
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idx %= bits_per_int();
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auto idx3 = idx;
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_storage[idx1][idx2] &= ~(int_type(1) << idx3);
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}
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void clear();
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};
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