random.cpp

来自「飞机场模拟系统」· C++ 代码 · 共 64 行

#include "Random.h"


int Random::reseed()
/*
Post: The seed is replaced by a pseudorandom successor.
*/
{
   seed = seed * multiplier + add_on;
   return seed;
}


Random::Random(bool pseudo)
/*
Post: The values of seed, add_on, and multiplier are
      initialized.  The seed is initialized randomly only if pseudo == false.
*/
{
   if (pseudo) seed = 1;
   else seed = time(NULL) % INT_MAX;
   multiplier = 2743;
   add_on = 5923;
}


double Random::random_real()
/*
Post: A random real number between 0 and 1 is returned.
*/
{
   double max = INT_MAX + 1.0;
   double temp = reseed();
   if (temp < 0) temp = temp + max;
   return temp / max;
}


int Random::random_integer(int low, int high)
/*
Post: A random integer between low and high (inclusive) is returned.
*/
{
   if (low > high) return random_integer(high, low);
   else return ((int) ((high - low + 1) * random_real())) + low;
}


int Random::poisson(double mean)
/*
Post: A random integer, reflecting a Poisson distribution
      with parameter mean, is returned.
*/
{
   double limit = exp(-mean);
   double product = random_real();
   int count = 0;
   while (product > limit) {
      count++;
      product *= random_real();
   }
   return count;
}