ImathRandom.h

//
// SPDX-License-Identifier: BSD-3-Clause
// Copyright Contributors to the OpenEXR Project.
//
 
//
// Generators for uniformly distributed pseudo-random numbers and
// functions that use those generators to generate numbers with
// non-uniform distributions
//
// Note: class Rand48() calls erand48() and nrand48(), which are not
// available on all operating systems.  For compatibility we include
// our own versions of erand48() and nrand48().  Our functions
// have been reverse-engineered from the corresponding Unix/Linux
// man page.
//
 
#ifndef INCLUDED_ATOMSMATHRANDOM_H
#define INCLUDED_ATOMSMATHRANDOM_H
 
#include <AtomsMath/ImathExport.h>
#include <AtomsMath/ImathNamespace.h>
 
#include <math.h>
#include <stdlib.h>
 
ATOMSMATH_INTERNAL_NAMESPACE_HEADER_ENTER
 
class ATOMSMATH_EXPORT Rand32
{
  public:
 
    ATOMSMATH_HOSTDEVICE Rand32 (unsigned long int seed = 0);
 
    ATOMSMATH_HOSTDEVICE void init (unsigned long int seed);
 
    ATOMSMATH_HOSTDEVICE bool nextb();
 
    ATOMSMATH_HOSTDEVICE unsigned long int nexti();
 
    ATOMSMATH_HOSTDEVICE float nextf();
 
    ATOMSMATH_HOSTDEVICE float nextf (float rangeMin, float rangeMax);
 
  private:
    ATOMSMATH_HOSTDEVICE void next();
 
    unsigned long int _state;
};
 
class Rand48
{
  public:
 
    ATOMSMATH_HOSTDEVICE Rand48 (unsigned long int seed = 0);
 
    ATOMSMATH_HOSTDEVICE void init (unsigned long int seed);
 
    ATOMSMATH_HOSTDEVICE bool nextb();
 
    ATOMSMATH_HOSTDEVICE long int nexti();
 
    ATOMSMATH_HOSTDEVICE double nextf();
 
    ATOMSMATH_HOSTDEVICE double nextf (double rangeMin, double rangeMax);
 
  private:
    unsigned short int _state[3];
};
 
template <class Vec, class Rand> ATOMSMATH_HOSTDEVICE Vec solidSphereRand (Rand& rand);
 
template <class Vec, class Rand> ATOMSMATH_HOSTDEVICE Vec hollowSphereRand (Rand& rand);
 
template <class Rand> ATOMSMATH_HOSTDEVICE float gaussRand (Rand& rand);
 
template <class Vec, class Rand> ATOMSMATH_HOSTDEVICE Vec gaussSphereRand (Rand& rand);
 
//---------------------------------
// erand48(), nrand48() and friends
//---------------------------------
 
#ifndef __APPLE__
ATOMSMATH_HOSTDEVICE ATOMSMATH_EXPORT double erand48 (unsigned short state[3]);
ATOMSMATH_HOSTDEVICE ATOMSMATH_EXPORT double drand48();
ATOMSMATH_HOSTDEVICE ATOMSMATH_EXPORT long int nrand48 (unsigned short state[3]);
ATOMSMATH_HOSTDEVICE ATOMSMATH_EXPORT long int lrand48();
ATOMSMATH_HOSTDEVICE ATOMSMATH_EXPORT void srand48 (long int seed);
#endif
 
//---------------
// Implementation
//---------------
 
inline void
Rand32::init (unsigned long int seed)
{
    _state = (seed * 0xa5a573a5L) ^ 0x5a5a5a5aL;
}
 
inline Rand32::Rand32 (unsigned long int seed)
{
    init (seed);
}
 
inline void
Rand32::next()
{
    _state = 1664525L * _state + 1013904223L;
}
 
inline bool
Rand32::nextb()
{
    next();
    // Return the 31st (most significant) bit, by and-ing with 2 ^ 31.
    return !!(_state & 2147483648UL);
}
 
inline unsigned long int
Rand32::nexti()
{
    next();
    return _state & 0xffffffff;
}
 
inline float
Rand32::nextf (float rangeMin, float rangeMax)
{
    float f = nextf();
    return rangeMin * (1 - f) + rangeMax * f;
}
 
inline void
Rand48::init (unsigned long int seed)
{
    seed = (seed * 0xa5a573a5L) ^ 0x5a5a5a5aL;
 
    _state[0] = (unsigned short int) (seed & 0xFFFF);
    _state[1] = (unsigned short int) ((seed >> 16) & 0xFFFF);
    _state[2] = (unsigned short int) (seed & 0xFFFF);
}
 
inline Rand48::Rand48 (unsigned long int seed)
{
    init (seed);
}
 
inline bool
Rand48::nextb()
{
    return nrand48 (_state) & 1;
}
 
inline long int
Rand48::nexti()
{
    return nrand48 (_state);
}
 
inline double
Rand48::nextf()
{
    return erand48 (_state);
}
 
inline double
Rand48::nextf (double rangeMin, double rangeMax)
{
    double f = nextf();
    return rangeMin * (1 - f) + rangeMax * f;
}
 
template <class Vec, class Rand>
Vec
solidSphereRand (Rand& rand)
{
    Vec v;
 
    do
    {
        for (unsigned int i = 0; i < Vec::dimensions(); i++)
            v[i] = (typename Vec::BaseType) rand.nextf (-1, 1);
    } while (v.length2() > 1);
 
    return v;
}
 
template <class Vec, class Rand>
Vec
hollowSphereRand (Rand& rand)
{
    Vec v;
    typename Vec::BaseType length;
 
    do
    {
        for (unsigned int i = 0; i < Vec::dimensions(); i++)
            v[i] = (typename Vec::BaseType) rand.nextf (-1, 1);
 
        length = v.length();
    } while (length > 1 || length == 0);
 
    return v / length;
}
 
template <class Rand>
float
gaussRand (Rand& rand)
{
    float x;       // Note: to avoid numerical problems with very small
    float y;       // numbers, we make these variables singe-precision
    float length2; // floats, but later we call the double-precision log()
                   // and sqrt() functions instead of logf() and sqrtf().
    do
    {
        x       = float (rand.nextf (-1, 1));
        y       = float (rand.nextf (-1, 1));
        length2 = x * x + y * y;
    } while (length2 >= 1 || length2 == 0);
 
    return x * sqrt (-2 * log (double (length2)) / length2);
}
 
template <class Vec, class Rand>
Vec
gaussSphereRand (Rand& rand)
{
    return hollowSphereRand<Vec> (rand) * gaussRand (rand);
}
 
ATOMSMATH_INTERNAL_NAMESPACE_HEADER_EXIT
 
#endif // INCLUDED_ATOMSMATHRANDOM_H