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author | upstream source tree <ports@midipix.org> | 2015-03-15 20:14:05 -0400 |
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committer | upstream source tree <ports@midipix.org> | 2015-03-15 20:14:05 -0400 |
commit | 554fd8c5195424bdbcabf5de30fdc183aba391bd (patch) | |
tree | 976dc5ab7fddf506dadce60ae936f43f58787092 /libstdc++-v3/testsuite/ext/pb_ds/example/store_hash.cc | |
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Diffstat (limited to 'libstdc++-v3/testsuite/ext/pb_ds/example/store_hash.cc')
-rw-r--r-- | libstdc++-v3/testsuite/ext/pb_ds/example/store_hash.cc | 97 |
1 files changed, 97 insertions, 0 deletions
diff --git a/libstdc++-v3/testsuite/ext/pb_ds/example/store_hash.cc b/libstdc++-v3/testsuite/ext/pb_ds/example/store_hash.cc new file mode 100644 index 000000000..f762bfdb2 --- /dev/null +++ b/libstdc++-v3/testsuite/ext/pb_ds/example/store_hash.cc @@ -0,0 +1,97 @@ +// -*- 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 store_hash_example.cpp + * An example showing how to store hash-values with + * each entry in a hash-based container. + */ + +/** + * This example shows how to configure a hash-based container to store + * the hash value of each key along with each entry. This technique + * is useful for complex keys (e.g., strings in this example), since + * it lowers the cost of collisions. For simpler types (e.g., integers), + * where the cost of comparing keys is of the same order as the cost + * of comparing hash values, this technique adds unnecessary overhead. + */ + +#include <functional> +#include <string> +#include <ext/pb_ds/assoc_container.hpp> +#include <ext/pb_ds/hash_policy.hpp> + +using namespace std; +using namespace __gnu_pbds; + +// A string hash functor. +struct string_hash : public unary_function<string, size_t> +{ + inline size_t + operator()(string str) const + { + string::const_iterator b = str.begin(); + string::const_iterator e = str.end(); + + size_t hash = 0; + while (b != e) + { + hash *= 5; + hash += static_cast<size_t>(*b); + ++b; + } + return hash; + } +}; + +int main() +{ + // A collision-chaining hash table mapping strings to ints. + typedef + cc_hash_table< + string, + int, + string_hash, + equal_to<string>, + direct_mask_range_hashing<>, + hash_standard_resize_policy<>, + true> + map_t; + + map_t h; + + // Use regularly. + h["Hello, "] = 0; + h["world"] = 1; + + return 0; +} + |