large_bitset.hh

/*
 * Copyright (C) 2015-present ScyllaDB
 */

/*
 * SPDX-License-Identifier: LicenseRef-ScyllaDB-Source-Available-1.0
 */

// A bitset containing a very large number of bits, so it uses fragmented
// storage in order not to stress the memory allocator.

#pragma once

#include <limits>
#include "utils/chunked_vector.hh"

class large_bitset {
    using int_type = uint64_t;
    static constexpr size_t bits_per_int() {
        return std::numeric_limits<int_type>::digits;
    }
    size_t _nr_bits = 0;
    utils::chunked_vector<int_type> _storage;
public:
    explicit large_bitset(size_t nr_bits);
    explicit large_bitset(size_t nr_bits, utils::chunked_vector<int_type> storage) : _nr_bits(nr_bits), _storage(std::move(storage)) {}
    large_bitset(large_bitset&&) = default;
    large_bitset(const large_bitset&) = delete;
    large_bitset& operator=(const large_bitset&) = delete;
    size_t size() const {
        return _nr_bits;
    }

    size_t memory_size() const {
        return _storage.memory_size();
    }

    bool test(size_t idx) const {
        auto idx1 = idx / bits_per_int();
        idx %= bits_per_int();
        auto idx2 = idx;
        return (_storage[idx1] >> idx2) & 1;
    }
    void set(size_t idx) {
        auto idx1 = idx / bits_per_int();
        idx %= bits_per_int();
        auto idx2 = idx;
        _storage[idx1] |= int_type(1) << idx2;
    }
    void clear(size_t idx) {
        auto idx1 = idx / bits_per_int();
        idx %= bits_per_int();
        auto idx2 = idx;
        _storage[idx1] &= ~(int_type(1) << idx2);
    }
    void clear();

    const utils::chunked_vector<int_type>& get_storage() const {
        return _storage;
    }
};