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/* $Id$ */
/** @file random_func.hpp Pseudo random number generator. */
#ifndef RANDOM_FUNC_HPP
#define RANDOM_FUNC_HPP
#if defined(__APPLE__)
/* Apple already has Random declared */
#define Random OTTD_Random
#endif /* __APPLE__ */
/**************
* Warning: DO NOT enable this unless you understand what it does
*
* If enabled, in a network game all randoms will be dumped to the
* stdout if the first client joins (or if you are a client). This
* is to help finding desync problems.
*
* Warning: DO NOT enable this unless you understand what it does
**************/
//#define RANDOM_DEBUG
/**
* Structure to encapsulate the pseudo random number generators.
*/
struct Randomizer {
/** The state of the randomizer */
uint32 state[2];
/**
* Generate the next pseudo random number
* @return the random number
*/
uint32 Next();
/**
* Generate the next pseudo random number scaled to max
* @param max the maximum value of the returned random number
* @return the random number
*/
uint32 Next(uint16 max);
/**
* (Re)set the state of the random number generator.
* @param seed the new state
*/
void SetSeed(uint32 seed);
};
extern Randomizer _random; ///< Random used in the game state calculations
extern Randomizer _interactive_random; ///< Random used every else where is does not (directly) influence the game state
/** Stores the state of all random number generators */
struct SavedRandomSeeds {
Randomizer random;
Randomizer interactive_random;
};
/** Saves the current seeds
* @param storage Storage for saving
*/
static inline void SaveRandomSeeds(SavedRandomSeeds *storage)
{
storage->random = _random;
storage->interactive_random = _interactive_random;
}
/** Restores previously saved seeds
* @param storage Storage where SaveRandomSeeds() stored th seeds
*/
static inline void RestoreRandomSeeds(const SavedRandomSeeds &storage)
{
_random = storage.random;
_interactive_random = storage.interactive_random;
}
void SetRandomSeed(uint32 seed);
#ifdef RANDOM_DEBUG
#define Random() DoRandom(__LINE__, __FILE__)
uint32 DoRandom(int line, const char *file);
#define RandomRange(max) DoRandomRange(max, __LINE__, __FILE__)
uint DoRandomRange(uint max, int line, const char *file);
#else
static FORCEINLINE uint32 Random()
{
return _random.Next();
}
static FORCEINLINE uint32 RandomRange(uint16 max)
{
return _random.Next(max);
}
#endif
static FORCEINLINE uint32 InteractiveRandom()
{
return _interactive_random.Next();
}
static FORCEINLINE uint32 InteractiveRandomRange(uint16 max)
{
return _interactive_random.Next(max);
}
/**
* Checks if a given randomize-number is below a given probability.
*
* This function is used to check if the given probability by the fraction of (a/b)
* is greater than low 16 bits of the given randomize-number r.
*
* Do not use this function twice on the same random 16 bits as it will yield
* the same result. One can use a random number for two calls to Chance16I,
* where one call sends the low 16 bits and the other the high 16 bits.
*
* @param a The numerator of the fraction
* @param b The denominator of the fraction, must of course not be null
* @param r The given randomize-number
* @return True if the probability given by r is less or equal to (a/b)
*/
static FORCEINLINE bool Chance16I(const uint a, const uint b, const uint32 r)
{
assert(b != 0);
return (((uint16)r * b + b / 2) >> 16) < a;
}
/**
* Flips a coin with a given probability.
*
* This macro can be used to get true or false randomized according to a
* given probability. The parameter a and b create a percent value with
* (a/b). The macro returns true in (a/b) percent.
*
* @see Chance16I()
* @param a The numerator of the fraction
* @param b The denominator of the fraction
* @return True in (a/b) percent
*/
static FORCEINLINE bool Chance16(const uint a, const uint b)
{
return Chance16I(a, b, Random());
}
/**
* Flips a coin with a given probability and saves the randomize-number in a variable.
*
* This function uses the same parameters as Chance16. The third parameter
* must be a variable the randomize-number from Random() is saved in.
*
* The low 16 bits of r will already be used and can therefor not be passed to
* Chance16I. One can only send the high 16 bits to Chance16I.
*
* @see Chance16I()
* @param a The numerator of the fraction
* @param b The denominator of the fraction
* @param r The variable to save the randomize-number from Random()
* @return True in (a/b) percent
*/
static FORCEINLINE bool Chance16R(const uint a, const uint b, uint32 &r)
{
r = Random();
return Chance16I(a, b, r);
}
#endif /* RANDOM_FUNC_HPP */
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