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pmaprand.h
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/* RCSid $Id: pmaprand.h,v 2.8 2017/08/14 21:12:10 rschregle Exp $ */
/*
======================================================================
Random number generators for photon distribution
Roland Schregle (roland.schregle@{hslu.ch, gmail.com})
(c) Fraunhofer Institute for Solar Energy Systems,
(c) Lucerne University of Applied Sciences and Arts,
supported by the Swiss National Science Foundation (SNSF, #147053)
======================================================================
$Id: pmaprand.h,v 2.8 2017/08/14 21:12:10 rschregle Exp $
*/
#ifndef PMAPRAND_H
#define PMAPRAND_H
/* According to the analytical validation, skipping sequential samples
* when sharing a single RNG among multiple sampling domains introduces
* overlapping photon rays (reported as 'duplicate keys' when building
* the underlying data structure) and therefore bias. This is aggravated
* when running parallel photon distribution subprocesses, where photon
* rays from different subprocesses may correlate.
* We therefore maintain a separate RNG state for each sampling domain
* (e.g. photon emission, scattering, and russian roulette). With
* multiprocessing, each subprocess has its own instance of the RNG
* state, which is independently seeded for decorellation -- see
* distribPhotons() and distribPhotonContrib().
* The pmapSeed() and pmapRandom() macros below can be adapted to
* platform-specific RNGs if necessary. */
#if defined(_WIN32) || defined(_WIN64)
/* Use standard RNG without state management; the generated sequences
* will be suboptimal */
#include "random.h"
#define pmapSeed(seed, state) srandom(seed)
#define pmapRandom(state) frandom()
#else
/* Assume NIX and manage RNG state via erand48() */
#define pmapSeed(seed, state) (state [0] += seed, state [1] += seed, \
state [2] += seed)
#define pmapRandom(state) erand48(state)
#endif
extern unsigned short partState [3], emitState [3], cntState [3],
mediumState [3], scatterState [3], rouletteState [3],
randSeed;
#endif
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