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Diffstat (limited to 'libstdc++-v3/testsuite/ext/pb_ds/example/hash_load_set_change.cc')
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1 files changed, 141 insertions, 0 deletions
diff --git a/libstdc++-v3/testsuite/ext/pb_ds/example/hash_load_set_change.cc b/libstdc++-v3/testsuite/ext/pb_ds/example/hash_load_set_change.cc new file mode 100644 index 00000000000..f8132e8e8db --- /dev/null +++ b/libstdc++-v3/testsuite/ext/pb_ds/example/hash_load_set_change.cc @@ -0,0 +1,141 @@ +// -*- C++ -*- + +// Copyright (C) 2005, 2006 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 2, 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 COPYING. If not, write to +// the Free Software Foundation, 59 Temple Place - Suite 330, Boston, +// MA 02111-1307, USA. + +// As a special exception, you may use this file as part of a free +// software library without restriction. Specifically, if other files +// instantiate templates or use macros or inline functions from this +// file, or you compile this file and link it with other files to +// produce an executable, this file does not by itself cause the +// resulting executable to be covered by the GNU General Public +// License. This exception does not however invalidate any other +// reasons why the executable file might be covered by the GNU General +// Public License. + +// 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_load_set_change_example.cpp + * An example of setting and changing the load factor of a hash-based + * container object. + */ + +/** + * This example shows how to set and change the load-factor of + * a hash-based container object through its resize-policy object. + */ + +#include <functional> +#include <cassert> +#include <ext/pb_ds/assoc_container.hpp> +#include <ext/pb_ds/hash_policy.hpp> + +using namespace std; +using namespace pb_ds; + +// A simple hash functor. +// hash could serve instead of this functor, but it is not yet +// standard everywhere. +struct int_hash : public unary_function<int, size_t> +{ + inline size_t + operator()(int i) const + { return i; } +}; + +int main() +{ + // A trigger policy type. + typedef hash_load_check_resize_trigger< true> trigger_t; + + // A resize policy type. + typedef + hash_standard_resize_policy< + hash_exponential_size_policy<>, + // Trigger type. + trigger_t, + /* Allow external access to size. + * This is not necessary for setting the load factor, + * but it allows to call get_actual_size. + */ + true> + resize_t; + + // A collision-chaining hash table mapping ints to chars. + typedef + cc_hash_table< + int, + char, + int_hash, + equal_to<int>, + // Combining function. + direct_mask_range_hashing<>, + // Resize policy. + resize_t> + map_t; + + // A trigger policy object with load between 0.3 and 0.8. + trigger_t trigger(static_cast<float>(0.3), static_cast<float>(0.8)); + + // A resize policy object with the above trigger. + resize_t resize(hash_exponential_size_policy<>(), + trigger); + + map_t r_c(int_hash(), + equal_to<int>(), + direct_mask_range_hashing<>(), + resize); + + r_c[1] = 'a'; + + // Check the loads and sizes. + assert(r_c.get_loads().first == static_cast<float>(0.3)); + assert(r_c.get_loads().second == static_cast<float>(0.8)); + assert(r_c.get_actual_size() == 8); + assert(r_c.size() == 1); + + // Note that there is a discrepancy between the loads of the policy + // object and the actual size of the container object. This is + // because the container's construction performs an implicit + // external resize. + r_c[2] = 'b'; + r_c[3] = 'c'; + r_c[4] = 'd'; + + assert(r_c.get_actual_size() == 8); + + // Change the loads. This causes (potentially) a resize. + r_c.set_loads(make_pair(static_cast<float>(0.01), + static_cast<float>(0.05))); + + // The actual size should really change in this case. + assert(r_c.get_actual_size() > 8); + + return 0; +} + |