From 57819d1dd98d23f2a59f59bdb752420b5ae11d52 Mon Sep 17 00:00:00 2001
From: Daniel James <daniel@calamity.org.uk>
Date: Sun, 23 Feb 2014 10:16:14 +0000
Subject: [PATCH] Always use prime policy for integers. Fixes trac #9282.

---
 include/boost/unordered/detail/buckets.hpp    | 40 +++++++++++++++++++
 include/boost/unordered/detail/equivalent.hpp |  4 +-
 include/boost/unordered/detail/unique.hpp     |  4 +-
 3 files changed, 44 insertions(+), 4 deletions(-)

diff --git a/include/boost/unordered/detail/buckets.hpp b/include/boost/unordered/detail/buckets.hpp
index 38c32f5a..6ad3808b 100644
--- a/include/boost/unordered/detail/buckets.hpp
+++ b/include/boost/unordered/detail/buckets.hpp
@@ -666,11 +666,51 @@ namespace boost { namespace unordered { namespace detail {
         typedef mix64_policy<std::size_t> type;
     };
 
+    template <typename T>
     struct pick_policy :
         pick_policy_impl<
             std::numeric_limits<std::size_t>::digits,
             std::numeric_limits<std::size_t>::radix> {};
 
+    // While the mix policy is generally faster, the prime policy is a lot
+    // faster when a large number consecutive integers are used, because
+    // there are no collisions. Since that is probably quite common, use
+    // prime policy for integeral types. But not the smaller ones, as they
+    // don't have enough unique values for this to be an issue.
+
+    template <>
+    struct pick_policy<int> {
+        typedef prime_policy<std::size_t> type;
+    };
+
+    template <>
+    struct pick_policy<unsigned int> {
+        typedef prime_policy<std::size_t> type;
+    };
+
+    template <>
+    struct pick_policy<long> {
+        typedef prime_policy<std::size_t> type;
+    };
+
+    template <>
+    struct pick_policy<unsigned long> {
+        typedef prime_policy<std::size_t> type;
+    };
+
+    // TODO: Maybe not if std::size_t is smaller than long long.
+#if !defined(BOOST_NO_LONG_LONG)
+    template <>
+    struct pick_policy<long long> {
+        typedef prime_policy<std::size_t> type;
+    };
+
+    template <>
+    struct pick_policy<unsigned long long> {
+        typedef prime_policy<std::size_t> type;
+    };
+#endif
+
     ////////////////////////////////////////////////////////////////////////////
     // Functions
 
diff --git a/include/boost/unordered/detail/equivalent.hpp b/include/boost/unordered/detail/equivalent.hpp
index ab175313..5b6cdfa6 100644
--- a/include/boost/unordered/detail/equivalent.hpp
+++ b/include/boost/unordered/detail/equivalent.hpp
@@ -146,7 +146,7 @@ namespace boost { namespace unordered { namespace detail {
         typedef boost::unordered::detail::grouped_table_impl<types> table;
         typedef boost::unordered::detail::set_extractor<value_type> extractor;
 
-        typedef boost::unordered::detail::pick_policy::type policy;
+        typedef boost::unordered::detail::pick_policy<T>::type policy;
     };
 
     template <typename A, typename K, typename M, typename H, typename P>
@@ -171,7 +171,7 @@ namespace boost { namespace unordered { namespace detail {
         typedef boost::unordered::detail::map_extractor<key_type, value_type>
             extractor;
 
-        typedef boost::unordered::detail::pick_policy::type policy;
+        typedef boost::unordered::detail::pick_policy<T>::type policy;
     };
 
     template <typename Types>
diff --git a/include/boost/unordered/detail/unique.hpp b/include/boost/unordered/detail/unique.hpp
index 88bbf0b6..67416a19 100644
--- a/include/boost/unordered/detail/unique.hpp
+++ b/include/boost/unordered/detail/unique.hpp
@@ -139,7 +139,7 @@ namespace boost { namespace unordered { namespace detail {
         typedef boost::unordered::detail::table_impl<types> table;
         typedef boost::unordered::detail::set_extractor<value_type> extractor;
 
-        typedef boost::unordered::detail::pick_policy::type policy;
+        typedef boost::unordered::detail::pick_policy<T>::type policy;
     };
 
     template <typename A, typename K, typename M, typename H, typename P>
@@ -164,7 +164,7 @@ namespace boost { namespace unordered { namespace detail {
         typedef boost::unordered::detail::map_extractor<key_type, value_type>
             extractor;
 
-        typedef boost::unordered::detail::pick_policy::type policy;
+        typedef boost::unordered::detail::pick_policy<T>::type policy;
     };
 
     template <typename Types>