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