rand/xorshift: add trivial xorshift RNG

Makefile.am

@@ -263,6 +263,8 @@ UTIL_FILES   =			\
     quaternion.cpp		\
     quaternion.hpp		\
     raii.hpp			\
+    rand/xorshift.cpp		\
+    rand/xorshift.hpp		\
     random.cpp			\
     random.hpp			\
     random.ipp			\
@@ -421,6 +423,7 @@ TEST_BIN = 			\
     test/point			\
     test/polynomial		\
     test/pool			\
+    test/rand/xorshift		\
     test/random			\
     test/range 			\
     test/rational		\

rand/xorshift.cpp

@@ -0,0 +1,66 @@
+/*
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ * Copyright 2015-2016 Danny Robson <danny@nerdcruft.net>
+ */
+
+#include "./xorshift.hpp"
+
+#include "../debug.hpp"
+
+#include <cstdint>
+
+using util::rand::xorshift;
+
+
+///////////////////////////////////////////////////////////////////////////////
+template <typename T>
+xorshift<T>::xorshift (T seed):
+    m_state (seed)
+{
+    // state must not be zero, or the period will be zero.
+    CHECK_NEZ (m_state);
+}
+
+
+///////////////////////////////////////////////////////////////////////////////
+namespace util { namespace rand {
+    template <>
+    uint32_t
+    xorshift<uint32_t>::operator() (void)
+    {
+        m_state ^= m_state << 13u;
+        m_state ^= m_state >> 17u;
+        m_state ^= m_state <<  5u;
+
+        return m_state;
+    }
+
+
+    //-----------------------------------------------------------------------------
+    template <>
+    uint64_t
+    xorshift<uint64_t>::operator() (void)
+    {
+        m_state ^= m_state << 13u;
+        m_state ^= m_state >>  7u;
+        m_state ^= m_state << 17u;
+
+        return m_state;
+    }
+} }
+
+
+///////////////////////////////////////////////////////////////////////////////
+template struct util::rand::xorshift<uint32_t>;
+template struct util::rand::xorshift<uint64_t>;

rand/xorshift.hpp

@@ -0,0 +1,38 @@
+/*
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ * Copyright 2015-2016 Danny Robson <danny@nerdcruft.net>
+ */
+
+#ifndef __UTIL_RAND_XORSHIFT_HPP
+#define __UTIL_RAND_XORSHIFT_HPP
+
+namespace util { namespace rand {
+    // implements a naive xorshift random generator.
+    //
+    // * does not comply with the c++11 rng class requirements
+    // * users may not rely on identical output across executions or library
+    //   updates. internal constants may change across releases
+    template <typename T>
+    struct xorshift {
+    public:
+        xorshift (T seed);
+
+        T operator() (void);
+
+    private:
+        T m_state;
+    };
+} }
+
+#endif