windows-server-2003/enduser/netmeeting/t120/mst120/randchnl.cpp

#include "precomp.h"
#include "fsdiag.h"
DEBUG_FILEZONE(ZONE_T120_MCSNC);
/*
 *	randchnl.cpp
 *
 *	Copyright (c) 1995 by DataBeam Corporation, Lexington, KY
 *
 *	Abstract:
 *		This is the implementation file for the RandomChannelGenerator class,
 *		which inherits from the RandomNumberGenerator class.  On instantiation,
 *		instances of this class will internally generate a random number which
 *		falls within the allowable range of dynamic channels values.  Channel
 *		assignments are then generated by incrementing this value each time a
 *		new assignment is requested.  Once the maximum allowable value has been
 *		assigned, the next value to be generated "wraps around" to the minimum
 *		allowable value.
 *
 *		Obviously, this class does not generate completely random channel
 *		values for each request.  With a completely random generator, it is
 *		possible to delete a channel in MCS, and then have the random number
 *		generator assign the same value as the deleted channel before all
 *		components of the system even know that the channel was deleted to
 *		start with, thus causing erratic behavior in the system.  In this
 *		class, no channel can be reassigned until all other possible channels
 *		have been assigned.
 *
 *		This class can be modifed in the future to incorporate additional
 *		"randomness" into the algorithm and still not reassign any channel
 *		numbers before all other possible values are used.  This, however,
 *		would be at the expense of performance and/or memory resources.
 *                  
 *	Caveats:
 *		None.
 *
 *	Author:
 *		Alan D. May
 */
#include "randchnl.h"

/*
 *	These macros define the mimimum and maximum allowable dynamic channel
 *	values.
 */
#define MINIMUM_DYNAMIC_CHANNEL		1001
#define MAXIMUM_DYNAMIC_CHANNEL		65535

/*
 *	RandomChannelGenerator ()
 *
 *	Public
 *
 *	Functional Description:
 *		This version of the constructor is used to create a random channel
 *		generator object that has been automatically seeded with the current
 *		time.
 */
RandomChannelGenerator::RandomChannelGenerator()
{
	Current_Channel = (GetTickCount() % (MAXIMUM_DYNAMIC_CHANNEL + 1 - MINIMUM_DYNAMIC_CHANNEL)) + MINIMUM_DYNAMIC_CHANNEL;
}

/*
 *	~RandomChannelGenerator ()
 *
 *	Public
 *
 *	Functional Description:
 *		This is the destructor for the RandomChannelGenerator class.
 */
RandomChannelGenerator::~RandomChannelGenerator ()
{
}

/*
 *	GetRandomChannel ()
 *
 *	Public
 *
 *	Functional Description:
 *		This method returns a valid dynamic channel number.
 */
RandomValue		RandomChannelGenerator::GetRandomChannel (Void)
{
	/*
	 *	Increment the current channel value.
	 */
	++Current_Channel;

	/*
	 *	Determine if the current channel value needs to wrap around.
	 */	if (Current_Channel > MAXIMUM_DYNAMIC_CHANNEL)
	{
		Current_Channel = MINIMUM_DYNAMIC_CHANNEL;
	}

	/*
	 *	Return the current channel value.
	 */
	return (Current_Channel);
}