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: bernoulli_distribution.hpp,v 1.19 2004/07/27 03:43:32 dgregor Exp $

    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 

    22 namespace boost {

    23 

    24 // Bernoulli distribution: p(true) = p, p(false) = 1-p   (boolean)

    25 template<class RealType = double>

    26 class bernoulli_distribution

    27 {

    28 public:

    29   // In principle, this could work with both integer and floating-point

    30   // types.  Generating floating-point random numbers in the first

    31   // place is probably more expensive, so use integer as input.

    32   typedef int input_type;

    33   typedef bool result_type;

    34 

    35   explicit bernoulli_distribution(const RealType& p = RealType(0.5)) 

    36     : _p(p)

    37   {

    38     assert(p >= 0);

    39     assert(p <= 1);

    40   }

    41 

    42   // compiler-generated copy ctor and assignment operator are fine

    43 

    44   RealType p() const { return _p; }

    45   void reset() { }

    46 

    47   template<class Engine>

    48   result_type operator()(Engine& eng)

    49   {

    50     if(_p == RealType(0))

    51       return false;

    52     else

    53       return RealType(eng() - (eng.min)()) <= _p * RealType((eng.max)()-(eng.min)());

    54   }

    55 

    56 #if !defined(BOOST_NO_OPERATORS_IN_NAMESPACE) && !defined(BOOST_NO_MEMBER_TEMPLATE_FRIENDS)

    57   template<class CharT, class Traits>

    58   friend std::basic_ostream<CharT,Traits>&

    59   operator<<(std::basic_ostream<CharT,Traits>& os, const bernoulli_distribution& bd)

    60   {

    61     os << bd._p;

    62     return os;

    63   }

    64 

    65   template<class CharT, class Traits>

    66   friend std::basic_istream<CharT,Traits>&

    67   operator>>(std::basic_istream<CharT,Traits>& is, bernoulli_distribution& bd)

    68   {

    69     is >> std::ws >> bd._p;

    70     return is;

    71   }

    72 #endif

    73 

    74 private:

    75   RealType _p;

    76 };

    77 

    78 } // namespace boost

    79 

    80 #endif // BOOST_RANDOM_BERNOULLI_DISTRIBUTION_HPP