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//========= Copyright Valve Corporation, All rights reserved. ============//
//
// Purpose: Basic random number generator
//
// $NoKeywords: $
//===========================================================================//
#include <time.h>
#include "Random.h"
// memdbgon must be the last include file in a .cpp file!!!
#include "tier0/memdbgon.h"
#define IA 16807
#define IM 2147483647
#define IQ 127773
#define IR 2836
#define NTAB 32
#define NDIV (1+(IM-1)/NTAB)
static long idum = 0;
void SeedRandomNumberGenerator(long lSeed)
{
if (lSeed)
{
idum = lSeed;
}
else
{
idum = -time(NULL);
}
if (1000 < idum)
{
idum = -idum;
}
else if (-1000 < idum)
{
idum -= 22261048;
}
}
long ran1(void)
{
int j;
long k;
static long iy=0;
static long iv[NTAB];
if (idum <= 0 || !iy)
{
if (-(idum) < 1) idum=1;
else idum = -(idum);
for (j=NTAB+7;j>=0;j--)
{
k=(idum)/IQ;
idum=IA*(idum-k*IQ)-IR*k;
if (idum < 0) idum += IM;
if (j < NTAB) iv[j] = idum;
}
iy=iv[0];
}
k=(idum)/IQ;
idum=IA*(idum-k*IQ)-IR*k;
if (idum < 0) idum += IM;
j=iy/NDIV;
iy=iv[j];
iv[j] = idum;
return iy;
}
// fran1 -- return a random floating-point number on the interval [0,1)
//
#define AM (1.0/IM)
#define EPS 1.2e-7
#define RNMX (1.0-EPS)
float fran1(void)
{
float temp = (float)AM*ran1();
if (temp > RNMX) return (float)RNMX;
else return temp;
}
#ifndef _XBOX
float RandomFloat( float flLow, float flHigh )
{
if (idum == 0)
{
SeedRandomNumberGenerator(0);
}
float fl = fran1(); // float in [0,1)
return (fl * (flHigh-flLow)) + flLow; // float in [low,high)
}
#endif
long RandomLong( long lLow, long lHigh )
{
if (idum == 0)
{
SeedRandomNumberGenerator(0);
}
unsigned long maxAcceptable;
unsigned long x = lHigh-lLow+1;
unsigned long n;
if (x <= 0 || MAX_RANDOM_RANGE < x-1)
{
return lLow;
}
// The following maps a uniform distribution on the interval [0,MAX_RANDOM_RANGE]
// to a smaller, client-specified range of [0,x-1] in a way that doesn't bias
// the uniform distribution unfavorably. Even for a worst case x, the loop is
// guaranteed to be taken no more than half the time, so for that worst case x,
// the average number of times through the loop is 2. For cases where x is
// much smaller than MAX_RANDOM_RANGE, the average number of times through the
// loop is very close to 1.
//
maxAcceptable = MAX_RANDOM_RANGE - ((MAX_RANDOM_RANGE+1) % x );
do
{
n = ran1();
} while (n > maxAcceptable);
return lLow + (n % x);
}
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