From e1c115c71ae7e02245d578c80f98408010e66bcd Mon Sep 17 00:00:00 2001
From: Danny Robson <danny@nerdcruft.net>
Date: Fri, 1 Jul 2016 17:01:21 +1000
Subject: [PATCH] murmur2: make mixing constexpr and inline

---
 hash/murmur/murmur2.cpp | 61 ++------------------------------
 hash/murmur/murmur2.hpp |  6 ++--
 hash/murmur/murmur2.ipp | 78 +++++++++++++++++++++++++++++++++++++++++
 3 files changed, 85 insertions(+), 60 deletions(-)
 create mode 100644 hash/murmur/murmur2.ipp

diff --git a/hash/murmur/murmur2.cpp b/hash/murmur/murmur2.cpp
index 2cc80061..79773fa3 100644
--- a/hash/murmur/murmur2.cpp
+++ b/hash/murmur/murmur2.cpp
@@ -21,61 +21,6 @@
 #include "common.hpp"
 
 
-///////////////////////////////////////////////////////////////////////////////
-template <typename T> struct constants { };
-
-template <>
-struct constants<uint32_t> {
-    static const uint32_t m = 0x5bd1e995;
-    static const  int32_t r = 24;
-};
-
-template <>
-struct constants<uint64_t> {
-    static const uint64_t m = 0xc6a4a7935bd1e995;
-    static const  int64_t r = 47;
-};
-
-
-/////////////////////////////////////////////////////////////////////
-uint32_t
-util::hash::murmur2::mix (uint32_t h, uint32_t k)
-{
-    static const uint32_t m = constants<uint32_t>::m;
-    static const uint32_t r = constants<uint32_t>::r;
-
-    k *= m;
-    k ^= k >> r;
-    k *= m;
-
-    h *= m;
-    h ^= k;
-
-    return h;
-}
-
-
-//-----------------------------------------------------------------------------
-// 64 bit murmur2 mixing function. Note the last two lines are swapped
-// compared with 32 bit murmur2_mix. It's not clear if this is deliberate
-// in the canonical implementation, so we just leave it to help compatibility.
-uint64_t
-util::hash::murmur2::mix (uint64_t h, uint64_t k)
-{
-    static const uint64_t m = constants<uint64_t>::m;
-    static const uint64_t r = constants<uint64_t>::r;
-
-    k *= m;
-    k ^= k >> r;
-    k *= m;
-
-    h ^= k;
-    h *= m;
-
-    return h;
-}
-
-
 ///////////////////////////////////////////////////////////////////////////////
 uint32_t
 util::hash::murmur2::hash_32 (const void *restrict key,
@@ -85,7 +30,7 @@ util::hash::murmur2::hash_32 (const void *restrict key,
     CHECK (key);
 
     // setup
-    static const auto m = constants<uint32_t>::m;
+    constexpr auto m = detail::constants<uint32_t>::m;
     uint32_t h = seed ^ uint32_t (len);
 
     // body
@@ -116,8 +61,8 @@ util::hash::murmur2::hash_64 (const void *restrict key,
                               uint64_t seed)
 {
     // setup
-    const auto m = constants<uint64_t>::m;
-    const auto r = constants<uint64_t>::r;
+    constexpr auto m = detail::constants<uint64_t>::m;
+    constexpr auto r = detail::constants<uint64_t>::r;
 
     uint64_t h = seed ^ (len * m);
 
diff --git a/hash/murmur/murmur2.hpp b/hash/murmur/murmur2.hpp
index 50973d8d..84fa4c3c 100644
--- a/hash/murmur/murmur2.hpp
+++ b/hash/murmur/murmur2.hpp
@@ -24,12 +24,14 @@
 // variants is deliberately not provided. You can damn well align your data or
 // fix the algorithm.
 namespace util { namespace hash { namespace murmur2 {
-    uint32_t mix (uint32_t, uint32_t);
-    uint64_t mix (uint64_t, uint64_t);
+    constexpr uint32_t mix (uint32_t, uint32_t);
+    constexpr uint64_t mix (uint64_t, uint64_t);
 
     uint32_t hash_32 (const void *restrict data, size_t len, uint32_t seed);
     uint64_t hash_64 (const void *restrict data, size_t len, uint64_t seed);
 } } }
 
+#include "./murmur2.ipp"
+
 #endif
 
diff --git a/hash/murmur/murmur2.ipp b/hash/murmur/murmur2.ipp
new file mode 100644
index 00000000..5af8a497
--- /dev/null
+++ b/hash/murmur/murmur2.ipp
@@ -0,0 +1,78 @@
+/*
+ * 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>
+ */
+
+#if defined(__UTIL_HASH_MURMUR_MURMUR2_IPP)
+#error
+#endif
+
+#define __UTIL_HASH_MURMUR_MURMUR2_IPP
+
+
+///////////////////////////////////////////////////////////////////////////////
+namespace util { namespace hash { namespace murmur2 { namespace detail {
+    template <typename T> struct constants;
+
+    template <>
+    struct constants<uint32_t> {
+        static const uint32_t m = 0x5bd1e995;
+        static const  int32_t r = 24;
+    };
+
+    template <>
+    struct constants<uint64_t> {
+        static const uint64_t m = 0xc6a4a7935bd1e995;
+        static const  int64_t r = 47;
+    };
+} } } }
+
+
+/////////////////////////////////////////////////////////////////////
+constexpr uint32_t
+util::hash::murmur2::mix (uint32_t h, uint32_t k)
+{
+    constexpr uint32_t m = detail::constants<uint32_t>::m;
+    constexpr uint32_t r = detail::constants<uint32_t>::r;
+
+    k *= m;
+    k ^= k >> r;
+    k *= m;
+
+    h *= m;
+    h ^= k;
+
+    return h;
+}
+
+
+//-----------------------------------------------------------------------------
+// 64 bit murmur2 mixing function. Note the last two lines are swapped
+// compared with 32 bit murmur2_mix. It's not clear if this is deliberate
+// in the canonical implementation, so we just leave it to help compatibility.
+constexpr uint64_t
+util::hash::murmur2::mix (uint64_t h, uint64_t k)
+{
+    constexpr uint64_t m = detail::constants<uint64_t>::m;
+    constexpr uint64_t r = detail::constants<uint64_t>::r;
+
+    k *= m;
+    k ^= k >> r;
+    k *= m;
+
+    h ^= k;
+    h *= m;
+
+    return h;
+}