Modified source engine (2017) developed by valve and leaked in 2020. Not for commercial purporses
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//========= Copyright Valve Corporation, All rights reserved. ============//
//
// Purpose: generates 4 randum numbers in the range 0..1 quickly, using SIMD
//
//=====================================================================================//
#include <math.h>
#include <float.h> // Needed for FLT_EPSILON
#include "basetypes.h"
#include <memory.h>
#include "tier0/dbg.h"
#include "mathlib/mathlib.h"
#include "mathlib/vector.h"
#include "mathlib/ssemath.h"
// memdbgon must be the last include file in a .cpp file!!!
#include "tier0/memdbgon.h"
// see knuth volume 3 for insight.
class SIMDRandStreamContext
{
fltx4 m_RandY[55];
fltx4 *m_pRand_J, *m_pRand_K;
public:
void Seed( uint32 seed )
{
m_pRand_J=m_RandY+23; m_pRand_K=m_RandY+54;
for(int i=0;i<55;i++)
{
for(int j=0;j<4;j++)
{
SubFloat( m_RandY[i], j) = (seed>>16)/65536.0;
seed=(seed+1)*3141592621u;
}
}
}
inline fltx4 RandSIMD( void )
{
// ret= rand[k]+rand[j]
fltx4 retval=AddSIMD( *m_pRand_K, *m_pRand_J );
// if ( ret>=1.0) ret-=1.0
fltx4 overflow_mask=CmpGeSIMD( retval, Four_Ones );
retval=SubSIMD( retval, AndSIMD( Four_Ones, overflow_mask ) );
*m_pRand_K = retval;
// update pointers w/ wrap-around
if ( --m_pRand_J < m_RandY )
m_pRand_J=m_RandY+54;
if ( --m_pRand_K < m_RandY )
m_pRand_K=m_RandY+54;
return retval;
}
};
#define MAX_SIMULTANEOUS_RANDOM_STREAMS 32
static SIMDRandStreamContext s_SIMDRandContexts[MAX_SIMULTANEOUS_RANDOM_STREAMS];
static volatile int s_nRandContextsInUse[MAX_SIMULTANEOUS_RANDOM_STREAMS];
void SeedRandSIMD(uint32 seed)
{
for( int i = 0; i<MAX_SIMULTANEOUS_RANDOM_STREAMS; i++)
s_SIMDRandContexts[i].Seed( seed+i );
}
fltx4 RandSIMD( int nContextIndex )
{
return s_SIMDRandContexts[nContextIndex].RandSIMD();
}
int GetSIMDRandContext( void )
{
for(;;)
{
for(int i=0; i < NELEMS( s_SIMDRandContexts ); i++)
{
if ( ! s_nRandContextsInUse[i] ) // available?
{
// try to take it!
if ( ThreadInterlockedAssignIf( &( s_nRandContextsInUse[i]), 1, 0 ) )
{
return i; // done!
}
}
}
Assert(0); // why don't we have enough buffers?
ThreadSleep();
}
}
void ReleaseSIMDRandContext( int nContext )
{
s_nRandContextsInUse[ nContext ] = 0;
}
fltx4 RandSIMD( void )
{
return s_SIMDRandContexts[0].RandSIMD();
}