rand/system;win32: add an RtlGenRandom generator

rand/system_win32.cpp

@@ -0,0 +1,37 @@
+/*
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/.
+ *
+ * Copyright 2019 Danny Robson <danny@nerdcruft.net>
+ */
+
+#include "system_win32.hpp"
+
+#include "win32/except.hpp"
+
+#include <windows.h>
+#include <ntsecapi.h>
+
+using cruft::rand::win32::rtlgenrandom;
+
+
+///////////////////////////////////////////////////////////////////////////////
+rtlgenrandom::rtlgenrandom ()
+{ ; }
+
+
+//-----------------------------------------------------------------------------
+rtlgenrandom::rtlgenrandom (std::string const &)
+{ ; }
+
+
+///////////////////////////////////////////////////////////////////////////////
+rtlgenrandom::result_type
+rtlgenrandom::operator() ()
+{
+    result_type res;
+    if (RtlGenRandom (&res, sizeof (res)) != TRUE)
+        cruft::win32::error::throw_code ();
+    return res;
+}

rand/system_win32.hpp

@@ -6,3 +6,34 @@
  * Copyright 2019 Danny Robson <danny@nerdcruft.net>
  */
 
+#pragma once
+
+#include <limits>
+#include <string>
+
+namespace cruft::rand {
+    namespace win32 {
+        /// Models std::random_device and is suitable as a drop-in replacement.
+        ///
+        /// This uses the RtlGenRandom function which is currently deprecated.
+        class rtlgenrandom {
+        public:
+            using result_type = unsigned;
+
+            rtlgenrandom ();
+            rtlgenrandom (std::string const&);
+            rtlgenrandom (rtlgenrandom const &) = delete;
+
+            rtlgenrandom& operator= (rtlgenrandom const&) = delete;
+
+            result_type operator() (void);
+
+            double entropy (void) const noexcept;
+
+            static constexpr result_type min (void) { return std::numeric_limits<result_type>::min (); }
+            static constexpr result_type max (void) { return std::numeric_limits<result_type>::max (); }
+        };
+    }
+
+    using system = win32::rtlgenrandom;
+}