rand: add mwc64x generator

Makefile.am

@@ -210,6 +210,8 @@ UTIL_FILES   =			\
     rand/lcg.hpp		\
     rand/xorshift.cpp		\
     rand/xorshift.hpp		\
+    rand/mwc64x.cpp		\
+    rand/mwc64x.hpp		\
     random.cpp			\
     random.hpp			\
     random.ipp			\

rand/mwc64x.cpp

@@ -0,0 +1,45 @@
+/*
+ * 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 2016 Danny Robson <danny@nerdcruft.net>
+ */
+
+
+#include "./mwc64x.hpp"
+
+#include "../debug.hpp"
+
+using util::rand::mwc64x;
+
+
+///////////////////////////////////////////////////////////////////////////////
+mwc64x::mwc64x (seed_type _seed):
+    m_state (_seed)
+{
+    CHECK_NEZ (m_state);
+}
+
+
+///////////////////////////////////////////////////////////////////////////////
+mwc64x::value_type
+mwc64x::operator() (void)
+{
+    CHECK_NEZ (m_state);
+
+    uint32_t c = m_state >> 32u;
+    uint32_t x = m_state & 0xFFFFFFFFu;
+
+    m_state = x * 4294883355ULL + c;
+
+    return x ^ c;
+}

rand/mwc64x.hpp

@@ -0,0 +1,43 @@
+/*
+ * 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 2016 Danny Robson <danny@nerdcruft.net>
+ */
+
+#ifndef __UTIL_RAND_MWC64X_HPP
+#define __UTIL_RAND_MWC64X_HPP
+
+#include <cstdint>
+
+namespace util { namespace rand {
+    // multiply-with-carry style generator suitable for rapid seeking and
+    // GPU generation.
+    //
+    // as with all such style generators, the seed value is very important.
+    // don't allow either half of the uint64_t to be zero.
+    struct mwc64x {
+    public:
+        using value_type = uint32_t;
+        using seed_type  = uint64_t;
+
+        mwc64x (seed_type);
+
+        value_type operator() (void);
+
+    private:
+        uint64_t m_state;
+    };
+} }
+
+
+#endif

test/rand/buckets.cpp

@@ -1,5 +1,6 @@
 #include "rand/xorshift.hpp"
 #include "rand/lcg.hpp"
+#include "rand/mwc64x.hpp"
 
 #include "tap.hpp"
 #include "maths.hpp"
@@ -15,9 +16,9 @@ template <>
 std::string
 type_to_string<util::rand::xorshift<uint64_t>> (void) { return "xorshift<uint64_t>"; }
 
-template <>
-std::string
-type_to_string<util::rand::lcg_t> (void) { return "lcg_t"; }
+template <> std::string type_to_string<util::rand::lcg_t> (void) { return "lcg_t"; }
+
+template <> std::string type_to_string<util::rand::mwc64x> (void) { return "mwc64x"; }
 
 
 ///////////////////////////////////////////////////////////////////////////////
@@ -43,9 +44,10 @@ test_buckets (util::TAP::logger &tap, Args&& ...args)
     for (unsigned i = 0; i < ITERATIONS; ++i)
         ++buckets[gen () & BUCKET_MASK];
 
-    tap.expect (std::find_if (std::cbegin (buckets),
+    tap.expect (
+        std::find_if (std::cbegin (buckets),
                       std::cend   (buckets),
-                              [] (auto v) { return v < EXPECTED * 3 / 4; }) == std::cend (buckets),
+                      [] (auto v) { return v < EXPECTED * 7 / 8; }) == std::cend (buckets),
         "bucket counts for %s", type_to_string<G> ());
 }
 
@@ -59,6 +61,7 @@ main (int,char**)
     test_buckets<util::rand::xorshift<uint32_t>> (tap, 0x1234u);
     test_buckets<util::rand::xorshift<uint64_t>> (tap, 0x1234u);
     test_buckets<util::rand::lcg_t> (tap, 0x1234u);
+    test_buckets<util::rand::mwc64x> (tap, 0x1234u);
 
     return tap.status ();
 }