boost/random/bernoulli_distribution.hpp

   1 /* boost random/bernoulli_distribution.hpp header file
   2  *
   3  * Copyright Jens Maurer 2000-2001
   4  * Distributed under the Boost Software License, Version 1.0. (See
   5  * accompanying file LICENSE_1_0.txt or copy at
   6  * http://www.boost.org/LICENSE_1_0.txt)
   7  *
   8  * See http://www.boost.org for most recent version including documentation.
   9  *
  10  * $Id$
  11  *
  12  * Revision history
  13  *  2001-02-18  moved to individual header files
  14  */
  15
  16 #ifndef BOOST_RANDOM_BERNOULLI_DISTRIBUTION_HPP
  17 #define BOOST_RANDOM_BERNOULLI_DISTRIBUTION_HPP
  18
  19 #include <cassert>
  20 #include <iostream>
  21 #include <boost/random/detail/config.hpp>
  22
  23 namespace boost {
  24
  25 // Bernoulli distribution: p(true) = p, p(false) = 1-p   (boolean)
  26 template<class RealType = double>
  27 class bernoulli_distribution
  28 {
  29 public:
  30   // In principle, this could work with both integer and floating-point
  31   // types.  Generating floating-point random numbers in the first
  32   // place is probably more expensive, so use integer as input.
  33   typedef int input_type;
  34   typedef bool result_type;
  35
  36   explicit bernoulli_distribution(const RealType& p_arg = RealType(0.5))
  37     : _p(p_arg)
  38   {
  39     assert(_p >= 0);
  40     assert(_p <= 1);
  41   }
  42
  43   // compiler-generated copy ctor and assignment operator are fine
  44
  45   RealType p() const { return _p; }
  46   void reset() { }
  47
  48   template<class Engine>
  49   result_type operator()(Engine& eng)
  50   {
  51     if(_p == RealType(0))
  52       return false;
  53     else
  54       return RealType(eng() - (eng.min)()) <= _p * RealType((eng.max)()-(eng.min)());
  55   }
  56
  57 #ifndef BOOST_RANDOM_NO_STREAM_OPERATORS
  58   template<class CharT, class Traits>
  59   friend std::basic_ostream<CharT,Traits>&
  60   operator<<(std::basic_ostream<CharT,Traits>& os, const bernoulli_distribution& bd)
  61   {
  62     os << bd._p;
  63     return os;
  64   }
  65
  66   template<class CharT, class Traits>
  67   friend std::basic_istream<CharT,Traits>&
  68   operator>>(std::basic_istream<CharT,Traits>& is, bernoulli_distribution& bd)
  69   {
  70     is >> std::ws >> bd._p;
  71     return is;
  72   }
  73 #endif
  74
  75 private:
  76   RealType _p;
  77 };
  78
  79 } // namespace boost
  80
  81 #endif // BOOST_RANDOM_BERNOULLI_DISTRIBUTION_HPP