109 lines
3.0 KiB
C++
109 lines
3.0 KiB
C++
/* boost random/uniform_smallint.hpp header file
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*
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* Copyright Jens Maurer 2000-2001
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* Distributed under the Boost Software License, Version 1.0. (See
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* accompanying file LICENSE_1_0.txt or copy at
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* http://www.boost.org/LICENSE_1_0.txt)
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*
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* See http://www.boost.org for most recent version including documentation.
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*
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* $Id: uniform_smallint.hpp 52492 2009-04-19 14:55:57Z steven_watanabe $
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*
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* Revision history
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* 2001-04-08 added min<max assertion (N. Becker)
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* 2001-02-18 moved to individual header files
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*/
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#ifndef BOOST_RANDOM_UNIFORM_SMALLINT_HPP
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#define BOOST_RANDOM_UNIFORM_SMALLINT_HPP
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#include <cassert>
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#include <iostream>
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#include <boost/config.hpp>
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#include <boost/limits.hpp>
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#include <boost/static_assert.hpp>
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#include <boost/random/detail/config.hpp>
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#include <boost/random/uniform_01.hpp>
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#include <boost/detail/workaround.hpp>
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namespace boost {
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// uniform integer distribution on a small range [min, max]
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template<class IntType = int>
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class uniform_smallint
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{
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public:
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typedef IntType input_type;
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typedef IntType result_type;
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explicit uniform_smallint(IntType min_arg = 0, IntType max_arg = 9)
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: _min(min_arg), _max(max_arg)
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{
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#ifndef BOOST_NO_LIMITS_COMPILE_TIME_CONSTANTS
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// MSVC fails BOOST_STATIC_ASSERT with std::numeric_limits at class scope
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BOOST_STATIC_ASSERT(std::numeric_limits<IntType>::is_integer);
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#endif
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}
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result_type min BOOST_PREVENT_MACRO_SUBSTITUTION () const { return _min; }
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result_type max BOOST_PREVENT_MACRO_SUBSTITUTION () const { return _max; }
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void reset() { }
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template<class Engine>
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result_type operator()(Engine& eng)
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{
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typedef typename Engine::result_type base_result;
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base_result _range = static_cast<base_result>(_max-_min)+1;
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base_result _factor = 1;
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// LCGs get bad when only taking the low bits.
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// (probably put this logic into a partial template specialization)
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// Check how many low bits we can ignore before we get too much
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// quantization error.
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base_result r_base = (eng.max)() - (eng.min)();
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if(r_base == (std::numeric_limits<base_result>::max)()) {
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_factor = 2;
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r_base /= 2;
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}
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r_base += 1;
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if(r_base % _range == 0) {
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// No quantization effects, good
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_factor = r_base / _range;
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} else {
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// carefully avoid overflow; pessimizing here
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for( ; r_base/_range/32 >= _range; _factor *= 2)
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r_base /= 2;
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}
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return ((eng() - (eng.min)()) / _factor) % _range + _min;
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}
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#ifndef BOOST_RANDOM_NO_STREAM_OPERATORS
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template<class CharT, class Traits>
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friend std::basic_ostream<CharT,Traits>&
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operator<<(std::basic_ostream<CharT,Traits>& os, const uniform_smallint& ud)
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{
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os << ud._min << " " << ud._max;
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return os;
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}
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template<class CharT, class Traits>
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friend std::basic_istream<CharT,Traits>&
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operator>>(std::basic_istream<CharT,Traits>& is, uniform_smallint& ud)
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{
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is >> std::ws >> ud._min >> std::ws >> ud._max;
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return is;
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}
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#endif
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private:
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result_type _min;
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result_type _max;
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};
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} // namespace boost
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#endif // BOOST_RANDOM_UNIFORM_SMALLINT_HPP
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