uuid.cc

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// -*- C++ -*-
#include <random>
#include <ctime>
#include <chrono>
#include "base/uuid.h"
 
#include <iostream>
 
namespace CNORXZ
{
 
    constexpr std::tm mkTRef()
    {
    std::tm o = {};
    o.tm_sec = 0;
    o.tm_min = 0;
    o.tm_hour = 0;
    o.tm_mday = 1;
    o.tm_mon = 0;
    o.tm_year = 70;
    o.tm_wday = 4;
    o.tm_yday = 0;
    o.tm_isdst = 0;
    return o;
    }
    
    // the node bits are created randomly (no search for mac or similar)
    Uuid mkUuid()
    {
    static constexpr uint64_t diff_1970_1582_ns =
        141427ull * 86400ull * 1000ull * 1000ull * 1000ull;
    static std::tm tref_1970 = mkTRef();
    static uint16_t version = 1;
    std::tm tref_1970_tmp = tref_1970;
    const auto ref = std::chrono::system_clock::from_time_t(std::mktime(&tref_1970_tmp));
    const auto now = std::chrono::system_clock::now();
    const uint64_t diff_ns = std::chrono::duration_cast<std::chrono::duration<uint64_t,std::nano>>
        (now - ref).count() + diff_1970_1582_ns;
 
    // following nomenclature of wikipedia
    const uint32_t time_low = diff_ns & 0xffffffff;
    const uint16_t time_mid = (diff_ns >> 32) & 0xffff;
    const uint16_t time_hi_and_version = ((diff_ns >> 48) & 0x0fff) | ( version << 12 );
    const uint8_t clock_seq_high_and_reserved = ((diff_ns >> 8) & 0x3f) | ( 0x02 << 6 );
    const uint8_t clock_seq_low = diff_ns & 0xff;
 
    static std::mt19937_64 gen {diff_ns};
    const uint64_t node = gen();
 
    const Uuid id =
        { ( static_cast<uint64_t>(time_low) << 32 ) |
          ( static_cast<uint64_t>(time_mid) << 16 ) |
          ( static_cast<uint64_t>(time_hi_and_version) ),
          ( static_cast<uint64_t>(clock_seq_high_and_reserved) << 56 ) |
          ( static_cast<uint64_t>(clock_seq_low) << 48 ) |
          ( node & 0xffffffffffff )
        };
    return id;
    }
}