rand/rdrand: add rdrand generator

CMakeLists.txt

@@ -440,6 +440,8 @@ list (
     rand/mwc64x.hpp
     rand/pcg.cpp
     rand/pcg.hpp
+    rand/rdrand.cpp
+    rand/rdrand.hpp
     rand/system.hpp
     random.cpp
     random.hpp

rand/rdrand.cpp

@@ -0,0 +1,44 @@
+/*
+ * 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 "rdrand.hpp"
+
+using cruft::rand::rdrand;
+
+
+///////////////////////////////////////////////////////////////////////////////
+rdrand::rdrand ()
+{ ; }
+
+
+//---------------------------------------------------------------------------------------
+rdrand::rdrand (std::string const &)
+    : rdrand ()
+{ ; }
+
+
+///////////////////////////////////////////////////////////////////////////////
+rdrand::result_type
+rdrand::operator() ()
+{
+    uint64_t res;
+    char success;
+
+    __asm__ __volatile__ (
+        "rdrand %0;"
+        "setc %1;"
+
+        : "=r" (res)
+        , "=qm" (success)
+    );
+
+    if (!__builtin_expect(success, 1))
+        throw std::runtime_error ("no value available for rdrand");
+
+    return res;
+}

rand/rdrand.hpp

@@ -0,0 +1,40 @@
+/*
+ * 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>
+ */
+
+#pragma once
+
+#include "../posix/fd.hpp"
+
+
+namespace cruft::rand {
+    /// Models std::random_device and is suitable as a drop-in replacement.
+    ///
+    /// This implementation assumes that the CPU supports the `rdrand`
+    /// instruction, and does not check that this is the case.
+    ///
+    /// It is safe to instantiatate the object even if the instructions are
+    /// not supported, but it is the users responsibility to prevent calls to
+    /// the object if this is not the case.
+    class rdrand {
+    public:
+        using result_type = unsigned;
+
+        rdrand ();
+        rdrand (std::string const&);
+        rdrand (rdrand const &) = delete;
+
+        rdrand& operator= (rdrand 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 (); }
+    };
+}

test/rand/buckets.cpp

@@ -55,6 +55,7 @@ main (int,char**)
     test_buckets<cruft::rand::mwc64x> (tap, 0x1234u);
     test_buckets<cruft::rand::pcg_xsh_rr<>> (tap, 0x1234u);
     test_buckets<cruft::rand::system> (tap);
+    test_buckets<cruft::rand::rdrand> (tap);
 
     return tap.status ();
 }