153 lines
3.8 KiB
C++
153 lines
3.8 KiB
C++
#ifndef BOOST_UUID_TIME_GENERATOR_V7_HPP_INCLUDED
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#define BOOST_UUID_TIME_GENERATOR_V7_HPP_INCLUDED
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// Copyright 2024 Peter Dimov
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// Distributed under the Boost Software License, Version 1.0.
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// https://www.boost.org/LICENSE_1_0.txt
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#include <boost/uuid/uuid.hpp>
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#include <boost/uuid/detail/chacha20.hpp>
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#include <boost/uuid/detail/random_provider.hpp>
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#include <boost/uuid/detail/endian.hpp>
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#include <random>
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#include <cstdint>
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#include <cstring>
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namespace boost {
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namespace uuids {
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// time_generator_v7
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class time_generator_v7
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{
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private:
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// Bit layout from high to low:
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// 48 bits: millisecond part of Unix epoch timestamp
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// 10 bits: microsecond part of Unix epoch timestamp
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// 6 bits: conflict resolution counter
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using state_type = std::uint64_t;
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state_type state_ = {};
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detail::chacha20_12 rng_;
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public:
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using result_type = uuid;
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time_generator_v7();
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time_generator_v7( time_generator_v7 const& rhs );
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time_generator_v7( time_generator_v7&& rhs ) noexcept;
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time_generator_v7& operator=( time_generator_v7 const& rhs ) noexcept;
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time_generator_v7& operator=( time_generator_v7&& rhs ) noexcept;
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result_type operator()() noexcept;
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private:
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static state_type get_new_state( state_type const& oldst ) noexcept;
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};
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// constructors
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inline time_generator_v7::time_generator_v7()
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{
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detail::random_provider seeder;
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rng_.seed( seeder );
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}
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inline time_generator_v7::time_generator_v7( time_generator_v7 const& rhs ): state_( rhs.state_ )
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{
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detail::random_provider seeder;
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rng_.seed( seeder );
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}
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inline time_generator_v7::time_generator_v7( time_generator_v7&& rhs ) noexcept: state_( std::move( rhs.state_ ) ), rng_( std::move( rhs.rng_ ) )
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{
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rhs.rng_.perturb();
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}
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// assignment
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inline time_generator_v7& time_generator_v7::operator=( time_generator_v7 const& rhs ) noexcept
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{
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state_ = rhs.state_;
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return *this;
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}
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inline time_generator_v7& time_generator_v7::operator=( time_generator_v7&& rhs ) noexcept
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{
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state_ = std::move( rhs.state_ );
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rng_ = std::move( rhs.rng_ );
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rhs.rng_.perturb();
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return *this;
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}
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// get_new_state
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inline time_generator_v7::state_type time_generator_v7::get_new_state( state_type const& oldst ) noexcept
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{
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// `now()` in microseconds
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std::uint64_t now_in_us = std::chrono::time_point_cast< std::chrono::microseconds >( std::chrono::system_clock::now() ).time_since_epoch().count();
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std::uint64_t time_ms = now_in_us / 1000; // timestamp, ms part
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std::uint64_t time_us = now_in_us % 1000; // timestamp, us part
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std::uint64_t newst = ( time_ms << 16 ) | ( time_us << 6 );
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// if the time has advanced, reset counter to zero
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if( newst > oldst )
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{
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return newst;
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}
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// if time_in_ms has gone backwards, we can't be monotonic
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if( time_ms < ( oldst >> 16 ) )
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{
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return newst;
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}
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// otherwise, use the old value and increment the counter
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return oldst + 1;
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}
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// operator()
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inline time_generator_v7::result_type time_generator_v7::operator()() noexcept
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{
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uuid result;
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// set lower 64 bits to random values
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std::uniform_int_distribution<std::uint32_t> dist;
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detail::store_native_u32( result.data + 8, dist( rng_ ) );
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detail::store_native_u32( result.data + 12, dist( rng_ ) );
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// get new timestamp
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state_ = get_new_state( state_ );
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std::uint64_t time_ms = state_ >> 16; // timestamp, ms part
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std::uint64_t time_us = ( state_ & 0xFFFF ) >> 6; // timestamp, us part
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std::uint64_t timestamp = ( time_ms << 16 ) | 0x7000 | time_us;
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detail::store_big_u64( result.data + 0, timestamp );
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// set variant and counter
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result.data[ 8 ] = static_cast< std::uint8_t >( 0x80 | ( state_ & 0x3F ) );
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return result;
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}
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}} // namespace boost::uuids
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#endif // BOOST_UUID_TIME_GENERATOR_V7_HPP_INCLUDED
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