src/core/random_func.hpp

   1 /* $Id: random_func.hpp 25893 2013-10-20 14:48:08Z fonsinchen $ */
   2
   3 /*
   4  * This file is part of OpenTTD.
   5  * OpenTTD 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, version 2.
   6  * OpenTTD 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.
   7  * See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with OpenTTD. If not, see <http://www.gnu.org/licenses/>.
   8  */
   9
  10 /** @file random_func.hpp Pseudo random number generator. */
  11
  12 #ifndef RANDOM_FUNC_HPP
  13 #define RANDOM_FUNC_HPP
  14
  15 #if defined(__APPLE__)
  16         /* Apple already has Random declared */
  17         #define Random OTTD_Random
  18 #endif /* __APPLE__ */
  19
  20 /**
  21  * Structure to encapsulate the pseudo random number generators.
  22  */
  23 struct Randomizer {
  24         /** The state of the randomizer */
  25         uint32 state[2];
  26
  27         uint32 Next();
  28         uint32 Next(uint32 limit);
  29         void SetSeed(uint32 seed);
  30 };
  31 extern Randomizer _random; ///< Random used in the game state calculations
  32 extern Randomizer _interactive_random; ///< Random used every else where is does not (directly) influence the game state
  33
  34 /** Stores the state of all random number generators */
  35 struct SavedRandomSeeds {
  36         Randomizer random;
  37         Randomizer interactive_random;
  38 };
  39
  40 /**
  41  * Saves the current seeds
  42  * @param storage Storage for saving
  43  */
  44 static inline void SaveRandomSeeds(SavedRandomSeeds *storage)
  45 {
  46         storage->random = _random;
  47         storage->interactive_random = _interactive_random;
  48 }
  49
  50 /**
  51  * Restores previously saved seeds
  52  * @param storage Storage where SaveRandomSeeds() stored th seeds
  53  */
  54 static inline void RestoreRandomSeeds(const SavedRandomSeeds &storage)
  55 {
  56         _random = storage.random;
  57         _interactive_random = storage.interactive_random;
  58 }
  59
  60 void SetRandomSeed(uint32 seed);
  61 #ifdef RANDOM_DEBUG
  62         #ifdef __APPLE__
  63                 #define OTTD_Random() DoRandom(__LINE__, __FILE__)
  64         #else
  65                 #define Random() DoRandom(__LINE__, __FILE__)
  66         #endif
  67         uint32 DoRandom(int line, const char *file);
  68         #define RandomRange(limit) DoRandomRange(limit, __LINE__, __FILE__)
  69         uint32 DoRandomRange(uint32 limit, int line, const char *file);
  70 #else
  71         static inline uint32 Random()
  72         {
  73                 return _random.Next();
  74         }
  75
  76         /**
  77          * Pick a random number between 0 and \a limit - 1, inclusive. That means 0
  78          * can be returned and \a limit - 1 can be returned, but \a limit can not be
  79          * returned.
  80          * @param limit Limit for the range to be picked from.
  81          * @return A random number in [0,\a limit).
  82          */
  83         static inline uint32 RandomRange(uint32 limit)
  84         {
  85                 return _random.Next(limit);
  86         }
  87 #endif
  88
  89 static inline uint32 InteractiveRandom()
  90 {
  91         return _interactive_random.Next();
  92 }
  93
  94 static inline uint32 InteractiveRandomRange(uint32 limit)
  95 {
  96         return _interactive_random.Next(limit);
  97 }
  98
  99 /**
 100  * Checks if a given randomize-number is below a given probability.
 101  *
 102  * This function is used to check if the given probability by the fraction of (a/b)
 103  * is greater than low 16 bits of the given randomize-number r.
 104  *
 105  * Do not use this function twice on the same random 16 bits as it will yield
 106  * the same result. One can use a random number for two calls to Chance16I,
 107  * where one call sends the low 16 bits and the other the high 16 bits.
 108  *
 109  * @param a The numerator of the fraction
 110  * @param b The denominator of the fraction, must of course not be null
 111  * @param r The given randomize-number
 112  * @return True if the probability given by r is less or equal to (a/b)
 113  */
 114 static inline bool Chance16I(const uint a, const uint b, const uint32 r)
 115 {
 116         assert(b != 0);
 117         return (((uint16)r * b + b / 2) >> 16) < a;
 118 }
 119
 120 /**
 121  * Flips a coin with given probability.
 122  *
 123  * This function returns true with (a/b) probability.
 124  *
 125  * @see Chance16I()
 126  * @param a The nominator of the fraction
 127  * @param b The denominator of the fraction
 128  * @return True with (a/b) probability
 129  */
 130 #ifdef RANDOM_DEBUG
 131         #define Chance16(a, b) Chance16I(a, b, DoRandom(__LINE__, __FILE__))
 132 #else
 133 static inline bool Chance16(const uint a, const uint b)
 134 {
 135         return Chance16I(a, b, Random());
 136 }
 137 #endif /* RANDOM_DEBUG */
 138
 139 /**
 140  * Flips a coin with a given probability and saves the randomize-number in a variable.
 141  *
 142  * This function uses the same parameters as Chance16. The third parameter
 143  * must be a variable the randomize-number from Random() is saved in.
 144  *
 145  * The low 16 bits of r will already be used and can therefore not be passed to
 146  * Chance16I. One can only send the high 16 bits to Chance16I.
 147  *
 148  * @see Chance16I()
 149  * @param a The numerator of the fraction
 150  * @param b The denominator of the fraction
 151  * @param r The variable to save the randomize-number from Random()
 152  * @return True in (a/b) percent
 153  */
 154 #ifdef RANDOM_DEBUG
 155         #define Chance16R(a, b, r) (r = DoRandom(__LINE__, __FILE__), Chance16I(a, b, r))
 156 #else
 157 static inline bool Chance16R(const uint a, const uint b, uint32 &r)
 158 {
 159         r = Random();
 160         return Chance16I(a, b, r);
 161 }
 162 #endif /* RANDOM_DEBUG */
 163
 164 #endif /* RANDOM_FUNC_HPP */