ceph/src/boost/boost/beast/core/detail/pcg.hpp

   1 //
   2 // Copyright (c) 2016-2019 Vinnie Falco (vinnie dot falco at gmail dot com)
   3 //
   4 // Distributed under the Boost Software License, Version 1.0. (See accompanying
   5 // file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
   6 //
   7 // Official repository: https://github.com/boostorg/beast
   8 //
   9
  10 #ifndef BOOST_BEAST_CORE_DETAIL_PCG_HPP
  11 #define BOOST_BEAST_CORE_DETAIL_PCG_HPP
  12
  13 #include <boost/core/ignore_unused.hpp>
  14 #include <cstdint>
  15 #include <random>
  16
  17 namespace boost {
  18 namespace beast {
  19 namespace detail {
  20
  21 class pcg
  22 {
  23     std::uint64_t state_ = 0;
  24     std::uint64_t increment_;
  25
  26 public:
  27     using result_type = std::uint32_t;
  28
  29     // Initialize the generator.
  30     // There are no restrictions on the input values.
  31     pcg(
  32         std::uint64_t seed,
  33         std::uint64_t stream)
  34     {
  35         // increment must be odd
  36         increment_ = 2 * stream + 1;
  37         boost::ignore_unused((*this)());
  38         state_ += seed;
  39         boost::ignore_unused((*this)());
  40     }
  41
  42     std::uint32_t
  43     operator()()
  44     {
  45         std::uint64_t const p = state_;
  46         state_ = p *
  47             6364136223846793005ULL +
  48             increment_;
  49         std::uint32_t const x =
  50             static_cast<std::uint32_t>(
  51             ((p >> 18) ^ p) >> 27);
  52         std::uint32_t const r = p >> 59;
  53     #ifdef BOOST_MSVC
  54         return _rotr(x, r);
  55     #else
  56         return (x >> r) | (x << ((1 + ~r) & 31));
  57     #endif
  58     }
  59 };
  60
  61 } // detail
  62 } // beast
  63 } // boost
  64
  65 #endif