118 lines
2.8 KiB
C
118 lines
2.8 KiB
C
/*
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random.c - random generator
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Copyright (C) 2007 Uncle Mike
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This program is free software: you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation, either version 3 of the License, or
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(at your option) any later version.
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This program is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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*/
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#include "common.h"
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static long idum = 0;
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#define MAX_RANDOM_RANGE 0x7FFFFFFFUL
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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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#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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void Com_SetRandomSeed( long lSeed )
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{
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if( lSeed ) idum = lSeed;
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else idum = -time( NULL );
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if( 1000 < idum )
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idum = -idum;
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else if( -1000 < idum )
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idum -= 22261048;
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}
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long lran1( 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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float fran1( void )
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{
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float temp = (float)AM * lran1();
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if( temp > RNMX )
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return (float)RNMX;
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return temp;
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}
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float Com_RandomFloat( float flLow, float flHigh )
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{
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float fl;
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if( idum == 0 ) Com_SetRandomSeed(0);
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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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long Com_RandomLong( long lLow, long lHigh )
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{
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dword maxAcceptable;
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dword n, x = lHigh-lLow + 1;
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if( idum == 0 ) Com_SetRandomSeed(0);
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if( x <= 0 || MAX_RANDOM_RANGE < x-1 )
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return lLow;
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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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maxAcceptable = MAX_RANDOM_RANGE - ((MAX_RANDOM_RANGE+1) % x );
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do
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{
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n = lran1();
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} while( n > maxAcceptable );
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return lLow + (n % x);
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} |