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/* RCSid $Id$ */ |
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/* |
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================================================================== |
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====================================================================== |
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Random number generators for photon distribution |
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Roland Schregle (roland.schregle@{hslu.ch, gmail.com}) |
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(c) Fraunhofer Institute for Solar Energy Systems, |
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(c) Lucerne University of Applied Sciences and Arts, |
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supported by the Swiss National Science Foundation (SNSF, #147053) |
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================================================================== |
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supported by the Swiss National Science Foundation (SNSF, #147053) |
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====================================================================== |
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$Id$ |
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*/ |
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#ifndef PMAPRAND_H |
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#define PMAPRAND_H |
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/* According to the analytical validation, skipping numbers in the sequence |
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introduces bias in scenes with high reflectance. We therefore use |
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erand48() with separate states for photon emission, scattering, and |
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russian roulette. The pmapSeed() and pmapRandom() macros can be |
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adapted to other (better?) RNGs. */ |
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#if defined(_WIN32) || defined(BSD) |
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/* Assume no erand48(), so use standard RNG without explicit multistate |
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control; the resulting sequences will be suboptimal */ |
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#include "random.h" |
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#define pmapSeed(seed, state) (srandom(seed)) |
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#define pmapRandom(state) (frandom()) |
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/* According to the analytical validation, skipping sequential samples |
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* when sharing a single RNG among multiple sampling domains introduces |
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* overlapping photon rays (reported as 'duplicate keys' when building |
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* the underlying data structure) and therefore bias. This is aggravated |
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* when running parallel photon distribution subprocesses, where photon |
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* rays from different subprocesses may correlate. |
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* We therefore maintain a separate RNG state for each sampling domain |
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* (e.g. photon emission, scattering, and russian roulette). With |
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* multiprocessing, each subprocess has its own instance of the RNG |
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* state, which is independently seeded for decorellation -- see |
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* distribPhotons() and distribPhotonContrib(). |
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* The pmapSeed() and pmapRandom() macros below can be adapted to |
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* platform-specific RNGs if necessary. */ |
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#if defined(_WIN32) || defined(_WIN64) |
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/* Use standard RNG without state management; the generated sequences |
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* will be suboptimal */ |
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#include "random.h" |
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#define pmapSeed(seed, state) srandom(seed) |
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#define pmapRandom(state) frandom() |
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#else |
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/* Assume NIX and manage RNG state via erand48() */ |
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#define pmapSeed(seed, state) (state [0] += seed, state [1] += seed, \ |
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state [2] += seed) |
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#define pmapRandom(state) erand48(state) |
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#define pmapRandom(state) erand48(state) |
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#endif |
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