00dae56e19
dynamic_bitset allocates only when constructed. then on it doesn't throw. Though not that accessing bits out of range is undefined behavior. Signed-off-by: Benny Halevy <bhalevy@scylladb.com>
69 lines
2.0 KiB
C++
69 lines
2.0 KiB
C++
/*
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* Copyright 2015-present ScyllaDB
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*/
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/*
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* SPDX-License-Identifier: AGPL-3.0-or-later
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*/
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#pragma once
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#include <limits>
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#include <vector>
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#include <seastar/core/align.hh>
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#include <seastar/core/bitops.hh>
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namespace utils {
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class dynamic_bitset {
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using int_type = uint64_t;
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static constexpr size_t bits_per_int = std::numeric_limits<int_type>::digits;
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static constexpr int_type all_set = std::numeric_limits<int_type>::max();
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static constexpr unsigned level_shift = seastar::log2ceil(bits_per_int);
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private:
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std::vector<std::vector<int_type>> _bits; // level n+1 = 64:1 summary of level n
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size_t _bits_count = 0;
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private:
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// For n in range 0..(bits_per_int-1), produces a mask with all bits < n set
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static int_type mask_lower_bits(size_t n) noexcept {
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return (int_type(1) << n) - 1;
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}
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// For n in range 0..(bits_per_int-1), produces a mask with all bits >= n set
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static int_type mask_higher_bits(size_t n) noexcept {
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return ~mask_lower_bits(n);
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}
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// For bit n, produce index into _bits[level]
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static size_t level_idx(unsigned level, size_t n) noexcept {
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return n >> ((level + 1) * level_shift);
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}
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// For bit n, produce bit number in _bits[level][level_idx]
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static unsigned level_remainder(unsigned level, size_t n) noexcept {
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return (n >> (level * level_shift)) & (bits_per_int - 1);
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}
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public:
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enum : size_t {
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npos = std::numeric_limits<size_t>::max()
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};
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public:
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explicit dynamic_bitset(size_t nr_bits);
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// undefined if n >= size
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bool test(size_t n) const noexcept {
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auto idx = n / bits_per_int;
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return _bits[0][idx] & (int_type(1u) << (n % bits_per_int));
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}
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// undefined if n >= size
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void set(size_t n) noexcept;
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// undefined if n >= size
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void clear(size_t n) noexcept;
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size_t size() const noexcept { return _bits_count; }
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size_t find_first_set() const noexcept;
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size_t find_next_set(size_t n) const noexcept;
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size_t find_last_set() const noexcept;
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};
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}
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