Merge unordered and hash from trunk.

- Only use Visual C++ pragma with appropriate compilers.
- Working link for Thomas Wang's hash function.
- Updated unordered rationale.
- Fix `unnecessary_copy_tests` for Visual C++ 12.
- Some extra insert tests.


[SVN r86728]

doc/rationale.qbk

@@ -3,7 +3,7 @@
  / file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt) ]
 
 [def __wang__
-    [@http://www.concentric.net/~Ttwang/tech/inthash.htm
+    [@http://web.archive.org/web/20121102023700/http://www.concentric.net/~Ttwang/tech/inthash.htm
     Thomas Wang's article on integer hash functions]]
 
 [section:rationale Implementation Rationale]
@@ -85,7 +85,8 @@ of 2.
 
 Using a prime number of buckets, and choosing a bucket by using the modulus
 of the hash function's result will usually give a good result. The downside
-is that the required modulus operation is fairly expensive.
+is that the required modulus operation is fairly expensive. This is what the
+containers do in most cases.
 
 Using a power of 2 allows for much quicker selection of the bucket
 to use, but at the expense of loosing the upper bits of the hash value.
@@ -95,12 +96,16 @@ functions this can't be relied on.
 
 To avoid this a transformation could be applied to the hash function, for an
 example see __wang__.  Unfortunately, a transformation like Wang's requires
-knowledge of the number of bits in the hash value, so it isn't portable enough.
-This leaves more expensive methods, such as Knuth's Multiplicative Method
-(mentioned in Wang's article). These don't tend to work as well as taking the
-modulus of a prime, and the extra computation required might negate
-efficiency advantage of power of 2 hash tables.
+knowledge of the number of bits in the hash value, so it isn't portable enough
+to use as a default. It can applicable in certain cases so the containers
+have a policy based implementation that can use this alternative technique.
 
-So, this implementation uses a prime number for the hash table size.
+Currently this is only done on 64 bit architecures, where prime number
+modulus can be expensive. Although this varies depending on the architecture,
+so I probably should revisit it.
+
+I'm also thinking of introducing a mechanism whereby a hash function can
+indicate that it's safe to be used directly with power of 2 buckets, in
+which case a faster plain power of 2 implementation can be used.
 
 [endsect]

test/unordered/insert_tests.cpp

@@ -576,6 +576,21 @@ UNORDERED_TEST(map_insert_range_test2,
 
 #if !defined(BOOST_NO_CXX11_HDR_INITIALIZER_LIST)
 
+struct initialize_from_two_ints
+{
+    int a, b;
+
+    friend std::size_t hash_value(initialize_from_two_ints const& x)
+    {
+        return x.a + x.b;
+    }
+
+    bool operator==(initialize_from_two_ints const& x) const
+    {
+        return a == x.a && b == x.b;
+    }
+};
+
 UNORDERED_AUTO_TEST(insert_initializer_list_set)
 {
     boost::unordered_set<int> set;
@@ -583,6 +598,30 @@ UNORDERED_AUTO_TEST(insert_initializer_list_set)
     BOOST_TEST_EQ(set.size(), 3u);
     BOOST_TEST(set.find(1) != set.end());
     BOOST_TEST(set.find(4) == set.end());
+
+    boost::unordered_set<initialize_from_two_ints> set2;
+
+    set2.insert({1, 2});
+    BOOST_TEST(set2.size() == 1);
+    BOOST_TEST(set2.find({1,2}) != set2.end());
+    BOOST_TEST(set2.find({2,1}) == set2.end());
+
+    set2.insert({{3,4},{5,6},{7,8}});
+    BOOST_TEST(set2.size() == 4);
+    BOOST_TEST(set2.find({1,2}) != set2.end());
+    BOOST_TEST(set2.find({3,4}) != set2.end());
+    BOOST_TEST(set2.find({5,6}) != set2.end());
+    BOOST_TEST(set2.find({7,8}) != set2.end());
+    BOOST_TEST(set2.find({8,7}) == set2.end());
+
+    set2.insert({{2, 1}, {3,4}});
+    BOOST_TEST(set2.size() == 5);
+    BOOST_TEST(set2.find({1,2}) != set2.end());
+    BOOST_TEST(set2.find({2,1}) != set2.end());
+    BOOST_TEST(set2.find({3,4}) != set2.end());
+    BOOST_TEST(set2.find({5,6}) != set2.end());
+    BOOST_TEST(set2.find({7,8}) != set2.end());
+    BOOST_TEST(set2.find({8,7}) == set2.end());
 }
 
 UNORDERED_AUTO_TEST(insert_initializer_list_multiset)

test/unordered/unnecessary_copy_tests.cpp

@@ -374,7 +374,7 @@ namespace unnecessary_copy_tests
         // COPY_COUNT(1) would be okay here.
         reset();
         x.emplace();
-#   if BOOST_WORKAROUND(BOOST_MSVC, >= 1700)
+#   if BOOST_WORKAROUND(BOOST_MSVC, == 1700)
         // This is a little odd, Visual C++ 11 seems to move the pair, which
         // results in one copy (for the const key) and one move (for the
         // non-const mapped value). Since 'emplace(boost::move(a))' (see below)