randgen.h

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#ifndef _RANDGEN_H
#define _RANDGEN_H


#include <ctime>        // for time()
#include <cstdlib> 
#include <iostream>
#include <cmath> 
#include <climits>  // for INT_MAX

// designed for implementation-independent randomization
// if all system-dependent calls included in this class, then
// other classes can make use of this class in independent manner
// all random numbers are uniformly distributed in given range
//
// RandGen() ---      constructor sets seed of random # generator
//                    once per program, not per class/object
//     
// RandInt(int max)
// RandInt(int low,int max) - return random integer in range [0..max)
//                     when one parameter used, [low..max] when
//                     two parameters used
//
//       examples:    rnd.RandInt(6) is random integer [0..5] or [0..6)
//                    rnd.RandInt(3,10) is random integer [3..10]
//                    rnd.RandInt()  is random integer [0..INT_MAX)
//
// RandReal()       -- returns random double in range [0..1)
// RandReal(double low, double max) -- random double in range [low..max)

class RandGen
{
  public:
    RandGen();                          // set seed for all instances
    int RandInt(int max = INT_MAX);     // returns int in [0..max)
    int RandInt(int low, int max);      // returns int in [low..max]
    double RandReal();                  // returns double in [0..1)
    double RandReal(double low, double max); // range [low..max]

    static void SetSeed(int seed);      // static (per class) seed set
private:
    static int ourInitialized;          // for 'per-class' initialization
};


/*************** DEFINITIONS ****************/

int RandGen::ourInitialized = 0;

void RandGen::SetSeed(int seed)
// postcondition: system srand() used to initialize seed
//                once per program (this is a static function)
{
    if (0 == ourInitialized)
    {   ourInitialized = 1;   // only call srand once
        srand(seed);          // randomize
    }
}


RandGen::RandGen()
// postcondition: system srand() used to initialize seed
//                once per program
{
    if (0 == ourInitialized)
    {   ourInitialized = 1;          // only call srand once
        srand(unsigned(time(0)));    // randomize
    }
}

int RandGen::RandInt(int max)
// precondition: max > 0
// postcondition: returns int in [0..max)
{
    return int(RandReal() * max);
}

int RandGen::RandInt(int low, int max)
// precondition: low <= max
// postcondition: returns int in [low..max]
{
    return low + RandInt(max-low+1);
}

double RandGen::RandReal()
// postcondition: returns double in [0..1)
{
    return rand() / (double(RAND_MAX) + 1);
}

double RandGen::RandReal(double low, double high)
{
    double width = fabs(high-low);
    double thelow = low < high ? low : high;
    return RandReal()*width + thelow;
}

#endif