BT411/engine/MUNGA/RANDOM.cpp

#include "munga.h"
#pragma hdrstop

#include "random.h"

int RandomGenerator::Numbers[250];
int RandomGenerator::Index = -1;

RandomGenerator Random;

//
//###########################################################################
//###########################################################################
//
void RandomGenerator::Init()
{
	int i, msb, mask;

	//
	//--------------------------------------------------------------------
	// After making sure the table is built only once, initialize the
	// Borland C++ random numbers with the low word of the current time in
	// milliseconds, and initialize the index pointer
	//--------------------------------------------------------------------
	//
	char *seed_spec = getenv("RANDOM");
	unsigned seed;
	if (seed_spec)
	{
		seed = (unsigned)atol(seed_spec);
	}
	else
	{
		seed = (unsigned)time(NULL);
	}
	#if defined(TEST_CLASS)
		cout << "Random Seed = " << seed << endl;
	#endif
	srand(seed);
	Index = 0;

	//
	//------------------------------------------------------------------
	// Load the random number buffer, then go thru and set the sign bit
	// randomly, increasing the range of random numbers from 0..32767 to
	// 0..65535
	//------------------------------------------------------------------
	//
	for (i=0; i<250; i++)
	{
		Numbers[i] = rand();
	}

	//
	//--------------------------------------------------------------------
	// In order to preserve a good random number mix for the XOR function,
	// mask and set the bits of 16 words in a descending manner as in
	// 1xx..., 01xx..., 001xx..., 0001xx..., ...
	//--------------------------------------------------------------------
	//
	mask = RAND_MAX >> 1;
	msb = mask + 1;
	int rand_size;
	for (rand_size=0; !(msb&(1<<rand_size)); ++rand_size);
	i = 14;
	while (rand_size--)
	{
		Verify(i<ELEMENTS(Numbers));
		Numbers[i] &= mask;
		Numbers[i] |= msb;
		mask >>= 1;
		msb >>= 1;
		i += 11;
	}
}

//
//###########################################################################
//###########################################################################
//
int RandomGenerator::GetRandomInt()
{
	int indent, result;

	//
	//------------------------------------------------------------------
	// The random number generated will be the result of an XOR with the
	// element 103 positions further (wrapping around) in the table
	//------------------------------------------------------------------
	//
	indent = (Index>=147)?Index-147:Index+103;
	result = Numbers[Index]^Numbers[indent];

	//
	//------------------------------------------------------------------------
	// Replace the current random number with the new one generated, increment
	// the buffer index pointer, and return the number
	//------------------------------------------------------------------------
	//
	Numbers[Index] = result;
	if (++Index == ELEMENTS(Numbers))
		Index=0;
	return result;
}

//
//###########################################################################
//###########################################################################
//
RandomGenerator::operator Scalar()
{
	Scalar result;

	result = GetRandomInt();
	result /= (float)(RAND_MAX + 1);
	return result;
}

//
//###########################################################################
//###########################################################################
//
int RandomGenerator::operator ()(int range)
{
	int result, max;

	max = RAND_MAX - ((RAND_MAX + 1)%range);
	do
	{
		result = GetRandomInt();
	} while (result>max);
	return result%range;
}

//
//###########################################################################
//###########################################################################
//
Die::Die(int n)
{
	dieSides = (n>1)?n:2;
	highestRandom = RAND_MAX - ((RAND_MAX+1)%dieSides);
}

//
//###########################################################################
//###########################################################################
//
Die::operator int()
{
	int result;

	//
	//------------------------------------------------------------------------
	// In order to not skew the probabilities to the low numbers, make sure
	// that the random # used is not greater than the limit determined for the
	// number of sides.
	//------------------------------------------------------------------------
	//
	do
	{
		result = Random.GetInt();
	} while (result>highestRandom);

	//
	//-------------------------------------------------------------------
	// Once the base random number is determined, do modulus division and
	// increment by 1 to map into the die range.
	//-------------------------------------------------------------------
	//
	return result % dieSides + 1;
}

#if defined(TEST_CLASS)
	#include "random.tcp"
#endif