Imported gcc-4.4.3

[msp430-gcc.git] / libstdc++-v3 / testsuite / ext / pb_ds / example / hash_shift_mask.cc

diff --git a/libstdc++-v3/testsuite/ext/pb_ds/example/hash_shift_mask.cc b/libstdc++-v3/testsuite/ext/pb_ds/example/hash_shift_mask.cc
new file mode 100644 (file)
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--- /dev/null
+++ b/libstdc++-v3/testsuite/ext/pb_ds/example/hash_shift_mask.cc
@@ -0,0 +1,108 @@
+// -*- C++ -*-
+
+// Copyright (C) 2005, 2006, 2009 Free Software Foundation, Inc.
+//
+// This file is part of the GNU ISO C++ Library.  This library is free
+// software; you can redistribute it and/or modify it under the terms
+// of the GNU General Public License as published by the Free Software
+// Foundation; either version 3, or (at your option) any later
+// version.
+
+// This library is distributed in the hope that it will be useful, but
+// WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+// General Public License for more details.
+
+// You should have received a copy of the GNU General Public License
+// along with this library; see the file COPYING3.  If not see
+// <http://www.gnu.org/licenses/>.
+
+
+// Copyright (C) 2004 Ami Tavory and Vladimir Dreizin, IBM-HRL.
+
+// Permission to use, copy, modify, sell, and distribute this software
+// is hereby granted without fee, provided that the above copyright
+// notice appears in all copies, and that both that copyright notice
+// and this permission notice appear in supporting documentation. None
+// of the above authors, nor IBM Haifa Research Laboratories, make any
+// representation about the suitability of this software for any
+// purpose. It is provided "as is" without express or implied
+// warranty.
+
+/**
+ * @file hash_shift_mask_example.cpp
+ * An example showing how to write a range-hasing functor.
+ */
+
+/**
+ * In some rare cases, advance knowledge of the distribution of keys allows
+ * writing more efficient hash-related policies.
+ * In the rather simplistic case of the example, it is known in advance that
+ * all keys have 0 two lowest bits. The example shows how to write
+ * a range-hashing function disregarding the two lowest bits of the hash value.
+ */
+
+#include <functional>
+#include <ext/pb_ds/assoc_container.hpp>
+#include <ext/pb_ds/hash_policy.hpp>
+
+using namespace std;
+using namespace __gnu_pbds;
+
+// A simple hash functor. hash could serve instead of this functor,
+// but it is not yet standard everywhere.
+struct simple_int_hash : public unary_function<int, size_t>
+{
+  inline size_t
+  operator()(int i) const
+  { return i; }
+};
+
+// A range-hashing function which shifts 2 bits right and then masks.
+class shift_two_mask_range_hashing : private direct_mask_range_hashing<>
+{
+public:
+  typedef size_t size_type;
+
+  // Swaps with a different instant.
+  void
+  swap(shift_two_mask_range_hashing& other)
+  { direct_mask_range_hashing<>::swap(other); }
+
+  // Called by the container when internally resized.
+  void
+  notify_resized(size_type size)
+  { direct_mask_range_hashing<>::notify_resized(size); }
+
+  // Given a hash value, returns a number in the range of the internal
+  // size of the container.
+  inline size_type
+  operator()(size_type hash) const
+  { return direct_mask_range_hashing<>::operator()(hash >> 2); }
+};
+
+int
+main()
+{
+  // A collision-chaining hash table mapping ints to chars.
+  typedef
+    cc_hash_table<
+    int,
+    char,
+    // Hash function.
+    simple_int_hash,
+    equal_to<int>,
+    // Range hashing function.
+    shift_two_mask_range_hashing>
+    map_t;
+
+  map_t h;
+
+  // Use normally.
+  h[16] = 'a';
+  h[256] = 'e';
+  h[4] = 'z';
+
+  return 0;
+}
+