From 27fb20f3abcd9250c66c7641ef2636f7513bbd99 Mon Sep 17 00:00:00 2001
From: Vinnie Falco <vinnie.falco@gmail.com>
Date: Sun, 4 Jan 2015 16:01:07 -0800
Subject: [PATCH] Add xor_shift_engine

---
 src/beast/beast/random/xor_shift_engine.h | 127 ++++++++++++++++++++++
 1 file changed, 127 insertions(+)
 create mode 100644 src/beast/beast/random/xor_shift_engine.h

diff --git a/src/beast/beast/random/xor_shift_engine.h b/src/beast/beast/random/xor_shift_engine.h
new file mode 100644
index 0000000000..3e02a86408
--- /dev/null
+++ b/src/beast/beast/random/xor_shift_engine.h
@@ -0,0 +1,127 @@
+//------------------------------------------------------------------------------
+/*
+    This file is part of Beast: https://github.com/vinniefalco/Beast
+    Copyright 2014, Vinnie Falco <vinnie.falco@gmail.com>
+
+    Permission to use, copy, modify, and/or distribute this software for any
+    purpose  with  or without fee is hereby granted, provided that the above
+    copyright notice and this permission notice appear in all copies.
+
+    THE  SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+    WITH  REGARD  TO  THIS  SOFTWARE  INCLUDING  ALL  IMPLIED  WARRANTIES  OF
+    MERCHANTABILITY  AND  FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+    ANY  SPECIAL ,  DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+    WHATSOEVER  RESULTING  FROM  LOSS  OF USE, DATA OR PROFITS, WHETHER IN AN
+    ACTION  OF  CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+    OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+*/
+//==============================================================================
+
+#ifndef BEAST_RANDOM_XOR_SHIFT_ENGINE_H_INCLUDED
+#define BEAST_RANDOM_XOR_SHIFT_ENGINE_H_INCLUDED
+
+#include <beast/config/CompilerConfig.h>
+#include <cstdint>
+#include <limits>
+#include <stdexcept>
+
+namespace beast {
+
+namespace detail {
+
+template <class = void>
+class xor_shift_engine
+{
+public:
+    using result_type = std::uint64_t;
+
+    xor_shift_engine(xor_shift_engine const&) = default;
+    xor_shift_engine& operator=(xor_shift_engine const&) = default;
+
+    explicit
+    xor_shift_engine (result_type val = 1977u);
+
+    void
+    seed (result_type seed);
+
+    result_type
+    operator()();
+
+    static 
+    result_type BEAST_CONSTEXPR
+    min()
+    {
+        return std::numeric_limits<result_type>::min();
+    }
+
+    static
+    result_type BEAST_CONSTEXPR
+    max()
+    {
+        return std::numeric_limits<result_type>::max();
+    }
+
+private:
+    result_type s_[2];
+
+    static
+    result_type
+    murmurhash3 (result_type x);
+};
+
+template <class _>
+xor_shift_engine<_>::xor_shift_engine (
+    result_type val)
+{
+    seed (val);
+}
+
+template <class _>
+void
+xor_shift_engine<_>::seed (result_type seed)
+{
+    if (seed == 0)
+        throw std::domain_error("invalid seed");
+    s_[0] = murmurhash3 (seed);
+    s_[1] = murmurhash3 (s_[0]);
+}
+
+template <class _>
+auto
+xor_shift_engine<_>::operator()() ->
+    result_type
+{
+    result_type s1 = s_[0];
+    result_type const s0 = s_[1];
+    s_[0] = s0;
+    s1 ^= s1 << 23;
+    return (s_[1] = (s1 ^ s0 ^ (s1 >> 17) ^ (s0 >> 26))) + s0;
+}
+
+template <class _>
+auto
+xor_shift_engine<_>::murmurhash3 (result_type x)
+    -> result_type
+{
+    x ^= x >> 33;
+    x *= 0xff51afd7ed558ccdULL;
+    x ^= x >> 33;
+    x *= 0xc4ceb9fe1a85ec53ULL;
+    return x ^= x >> 33;
+}
+
+} // detail
+
+/** XOR-shift Generator.
+
+    Meets the requirements of UniformRandomNumberGenerator.
+
+    Simple and fast RNG based on:
+    http://xorshift.di.unimi.it/xorshift128plus.c
+    does not accept seed==0
+*/
+using xor_shift_engine = detail::xor_shift_engine<>;
+
+}
+
+#endif