Fast prng is pcg

CHANGELOG.md

@@ -6,6 +6,7 @@ Version 217:
 * Fix file_body_win32
 * Use async_initiate
 * Check BOOST_NO_CXX11_THREAD_LOCAL
+* Fast prng is pcg
 
 --------------------------------------------------------------------------------
 

include/boost/beast/core/detail/pcg.hpp

@@ -0,0 +1,65 @@
+//
+// Copyright (c) 2016-2019 Vinnie Falco (vinnie dot falco at gmail dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+// Official repository: https://github.com/boostorg/beast
+//
+
+#ifndef BOOST_BEAST_CORE_DETAIL_PCG_HPP
+#define BOOST_BEAST_CORE_DETAIL_PCG_HPP
+
+#include <boost/core/ignore_unused.hpp>
+#include <cstdint>
+#include <random>
+
+namespace boost {
+namespace beast {
+namespace detail {
+
+class pcg
+{
+    std::uint64_t state_ = 0;
+    std::uint64_t increment_;
+
+public:
+    using result_type = std::uint32_t;
+
+    // Initialize the generator.
+    // There are no restrictions on the input values.
+    pcg(
+        std::uint64_t seed,
+        std::uint64_t stream)
+    {
+        // increment must be odd
+        increment_ = 2 * stream + 1;
+        boost::ignore_unused((*this)());
+        state_ += seed;
+        boost::ignore_unused((*this)());
+    }
+
+    std::uint32_t
+    operator()()
+    {
+        std::uint64_t const p = state_;
+        state_ = p *
+            6364136223846793005ULL +
+            increment_;
+        std::uint32_t const x =
+            static_cast<std::uint32_t>(
+            ((p >> 18) ^ p) >> 27);
+        std::uint32_t const r = p >> 59;
+    #ifdef BOOST_MSVC
+        return _rotr(x, r);
+    #else
+        return (x >> r) | (x << ((1 + ~r) & 31));
+    #endif
+    }
+};
+
+} // detail
+} // beast
+} // boost
+
+#endif

include/boost/beast/websocket/detail/impl/prng.ipp

@@ -11,6 +11,7 @@
 #define BOOST_BEAST_WEBSOCKET_DETAIL_IMPL_PRNG_IPP
 
 #include <boost/beast/core/detail/chacha.hpp>
+#include <boost/beast/core/detail/pcg.hpp>
 #include <boost/align/aligned_alloc.hpp>
 #include <boost/throw_exception.hpp>
 #include <atomic>
@@ -119,21 +120,25 @@ make_prng_no_tls(bool secure)
     class fast_prng final : public prng
     {
         int refs_ = 0;
-        std::minstd_rand r_;
+        beast::detail::pcg r_;
 
     public:
         fast_prng* next = nullptr;
 
         fast_prng()
-            : r_([]
+            : r_(
-                {
+                []{
-                    static std::atomic<
-                        std::uint64_t> nonce{0};
                     auto const pv = prng_seed();
-                    return static_cast<value_type>(
+                    return
-                        pv[0] + pv[1] + pv[2] + pv[3] +
+                        ((static_cast<std::uint64_t>(pv[0])<<32)+pv[1]) ^
-                        pv[4] + pv[5] + pv[6] + pv[7] +
+                        ((static_cast<std::uint64_t>(pv[2])<<32)+pv[3]) ^
-                        ++nonce);
+                        ((static_cast<std::uint64_t>(pv[4])<<32)+pv[5]) ^
+                        ((static_cast<std::uint64_t>(pv[6])<<32)+pv[7]);
+                }(),
+                []{
+                    static std::atomic<
+                        std::uint32_t> nonce{0};
+                    return ++nonce;
                 }())
         {
         }
@@ -215,19 +220,23 @@ make_prng_tls(bool secure)
 {
     class fast_prng final : public prng
     {
-        std::minstd_rand r_;
+        beast::detail::pcg r_;
 
     public:
         fast_prng()
-            : r_([]
+            : r_(
-                {
+                []{
-                    static std::atomic<
-                        std::uint64_t> nonce{0};
                     auto const pv = prng_seed();
-                    return static_cast<value_type>(
+                    return
-                        pv[0] + pv[1] + pv[2] + pv[3] +
+                        ((static_cast<std::uint64_t>(pv[0])<<32)+pv[1]) ^
-                        pv[4] + pv[5] + pv[6] + pv[7] +
+                        ((static_cast<std::uint64_t>(pv[2])<<32)+pv[3]) ^
-                        ++nonce);
+                        ((static_cast<std::uint64_t>(pv[4])<<32)+pv[5]) ^
+                        ((static_cast<std::uint64_t>(pv[6])<<32)+pv[7]);
+                }(),
+                []{
+                    static std::atomic<
+                        std::uint32_t> nonce{0};
+                    return ++nonce;
                 }())
         {
         }