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>
130 lines
3.1 KiB
C++
130 lines
3.1 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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#include <seastar/core/bitops.hh>
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#include <seastar/core/align.hh>
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#include <boost/range/adaptor/reversed.hpp>
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#include <boost/range/irange.hpp>
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#include "utils/dynamic_bitset.hh"
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#include "seastarx.hh"
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namespace utils {
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void dynamic_bitset::set(size_t n) noexcept {
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for (auto& level : _bits) {
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auto idx = n / bits_per_int;
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auto old = level[idx];
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level[idx] |= int_type(1u) << (n % bits_per_int);
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if (old) {
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break;
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}
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n = idx; // prepare for next level
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}
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}
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void dynamic_bitset::clear(size_t n) noexcept {
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for (auto& level : _bits) {
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auto idx = n / bits_per_int;
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auto old = level[idx];
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level[idx] &= ~(int_type(1u) << (n % bits_per_int));
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if (!old || level[idx]) {
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break;
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}
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n = idx; // prepare for next level
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}
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}
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size_t dynamic_bitset::find_first_set() const noexcept
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{
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size_t pos = 0;
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for (auto& vv : _bits | boost::adaptors::reversed) {
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auto v = vv[pos];
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pos *= bits_per_int;
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if (v) {
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pos += count_trailing_zeros(v);
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} else {
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return npos;
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}
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}
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return pos;
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}
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size_t dynamic_bitset::find_next_set(size_t n) const noexcept
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{
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++n;
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unsigned level = 0;
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unsigned nlevels = _bits.size();
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// Climb levels until we find a set bit in the right place
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while (level != nlevels) {
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if (n >= _bits_count) {
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return npos;
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}
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auto v = _bits[level][level_idx(level, n)];
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v &= ~mask_lower_bits(level_remainder(level, n));
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if (v) {
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break;
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}
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++level;
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n = align_up(n, size_t(1) << (level_shift * level));
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}
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if (level == nlevels) {
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return npos;
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}
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// Descend levels until we reach level 0
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do {
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auto v = _bits[level][level_idx(level, n)];
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v &= ~mask_lower_bits(level_remainder(level, n));
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n = align_down(n, size_t(1) << (level_shift * (level + 1)));
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n += count_trailing_zeros(v) << (level_shift * level);
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} while (level-- != 0);
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return n;
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}
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size_t dynamic_bitset::find_last_set() const noexcept
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{
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size_t pos = 0;
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for (auto& vv : _bits | boost::adaptors::reversed) {
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auto v = vv[pos];
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pos *= bits_per_int;
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if (v) {
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pos += bits_per_int - 1 - count_leading_zeros(v);
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} else {
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return npos;
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}
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}
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return pos;
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}
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dynamic_bitset::dynamic_bitset(size_t nr_bits)
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: _bits_count(nr_bits)
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{
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auto div_ceil = [] (size_t num, size_t den) {
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return (num + den - 1) / den;
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};
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// 1-64: 1 level
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// 65-4096: 2 levels
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// 4097-262144: 3 levels
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// etc.
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unsigned nr_levels = div_ceil(log2ceil(align_up(nr_bits, size_t(bits_per_int))), level_shift);
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_bits.resize(nr_levels);
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size_t level_bits = nr_bits;
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for (unsigned level = 0; level != nr_levels; ++level) {
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auto level_words = align_up(level_bits, bits_per_int) / bits_per_int;
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_bits[level].resize(level_words);
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level_bits = level_words; // for next iteration
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}
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}
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}
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