windows-server-2003/enduser/sakit/common/inc/randgen.h

/*
 * FILE: RandGen.h 
 * 
 * PURPOSE: Header file for a random number generator, based on
 *          original code by George Marsaglia.
 *
 * AUTHOR: Karl Denninghoff, November 1998
 *
 * Copyright: Microsoft Corporation, 1998
 */


#ifndef RANDGEN_H
#define RANDGEN_H


#ifndef _BASETSD_H_ // if the base sized types not defined (header file not included)
    typedef unsigned __int32 UINT32 ;
#endif

typedef unsigned __int16 UINT16 ;

    // maximum number returned by RandInt()
const UINT32 MAX_RANDGEN = 0xffffffffL; 

//-------------------------------------------------------------
//
// CLASS CSARandGen
//
// PURPOSE: Generates random numbers of 32 bits with a period of
//          about 2^250. However, since the seed is 32 bits, there
//          are only 2^32 different possible sequences accessible
//          through the interface provided.
//
// USAGE RULES and REMARKS: 
//       1) You may have as many instances (random number generators)
//          as you wish simultneously in a process.
//       2) The code is not thread-safe, i.e., you must not make
//          simultaneous calls to a particular random number generator
//          (CSARandGen instance) on different threads. If more than 
//          one thread is to call a particular generator, you should 
//          provide the synchronization necessary in some wrapper class.
//       3) Generation and subsequent conversion to a random real 
//          uniformly distributed over the interval [0,1] is provided 
//          by the RandReal() member function.
//       4) If you do not explicitly seed the generator, then the sequence
//          generated will with high probability be indestinguishable from
//          sequences generated by another instance. It will be an 
//          unrelated sequence that you will not be able to re-generate.
//       5) The constructor seeds the generator automatically using 
//          system clock input. However, it does not tell you this value.
//          If you want a random seed (one you likely have not used before) and
//          you also want to be able to repeat the sequence later, then
//          the following technique will work well.
//
//          CSARandGen *pRandGen = new CSARandGen;
//          UINT32 ulSeed = pRandGen->RandInt(); // gets a random seed value
//          pRandGen->RandSeed( ulSeed );
//              // now save ulSeed so you can use it again to seed
//              // a generator. Any CSARandGen instance will produce
//              // the same sequence after calling the seed function
//              // with the same seed value.
//
//
class CSARandGen {
    public: // public functions
        _stdcall CSARandGen();

            // seeds the random number generator, can be called at 
            // any time to re-seed, seeding with the same number starts
            // the same sequence. 
        void _stdcall RandSeed( UINT32 ulSeed );

            // returns uniformly distributed random number 
            // between 0 and MAX_RANDGEN inclusive, period about 2^250
        UINT32 _stdcall RandInt(); 

            // returns uniformly distributed random floating point number
            // between 0 and 1. Two adjacent possible numbers are 
            // 1/MAX_RANDGEN apart.
        double _stdcall RandReal()
        {
            return double(RandInt())/double(MAX_RANDGEN);
        };


    private: // private data members
        UINT16 mother1[10];
        UINT16 mother2[10];
        static LONG slCInstances; // keeps count of instantiations, used to ensure
                                  // uniqueness of default seeds when two instantiations
                                  // result in the same tick and filetime.
};

#endif