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102 lines
4.1 KiB
C++
102 lines
4.1 KiB
C++
#ifndef OPENMC_RANDOM_LCG_H
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#define OPENMC_RANDOM_LCG_H
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#include <cstdint>
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namespace openmc {
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//==============================================================================
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// Module constants.
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//==============================================================================
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constexpr int N_STREAMS {4};
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constexpr int STREAM_TRACKING {0};
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constexpr int STREAM_SOURCE {1};
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constexpr int STREAM_URR_PTABLE {2};
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constexpr int STREAM_VOLUME {3};
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constexpr int64_t DEFAULT_SEED {1};
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//==============================================================================
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//! Generate a pseudo-random number using a linear congruential generator.
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//! @param seed Pseudorandom number seed pointer
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//! @return A random number between 0 and 1
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//==============================================================================
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double prn(uint64_t* seed);
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//==============================================================================
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//! Generate a random number which is 'n' times ahead from the current seed.
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//!
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//! The result of this function will be the same as the result from calling
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//! `prn()` 'n' times, though without the side effect of altering the RNG
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//! state.
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//! @param n The number of RNG seeds to skip ahead by
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//! @param seed Pseudorandom number seed
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//! @return A random number between 0 and 1
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//==============================================================================
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double future_prn(int64_t n, uint64_t seed);
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//==============================================================================
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//! Set a RNG seed to a unique value based on a unique particle ID by striding
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//! the seed.
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//! @param id The particle ID
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//! @param offset The offset from the master seed to be used (e.g., for creating
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//! different streams)
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//! @return The initialized seed value
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//==============================================================================
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uint64_t init_seed(int64_t id, int offset);
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//==============================================================================
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//! Set the RNG seeds to unique values based on the ID of the particle. This
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//! function initializes the seeds for all RNG streams of the particle via
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//! striding.
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//! @param seeds Pseudorandom number seed array
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//! @param id The particle ID
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//==============================================================================
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void init_particle_seeds(int64_t id, uint64_t* seeds);
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//==============================================================================
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//! Advance the random number seed 'n' times from the current seed. This
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//! differs from the future_prn() function in that this function does alter
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//! the RNG state.
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//! @param seed Pseudorandom number seed pointer
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//! @param n The number of RNG seeds to skip ahead by
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//==============================================================================
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void advance_prn_seed(int64_t n, uint64_t* seed);
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//==============================================================================
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//! Advance a random number seed 'n' times.
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//!
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//! This is usually used to skip a fixed number of random numbers (the stride)
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//! so that a given particle always has the same starting seed regardless of
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//! how many processors are used.
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//! @param n The number of RNG seeds to skip ahead by
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//! @param seed The starting to seed to advance from
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//==============================================================================
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uint64_t future_seed(uint64_t n, uint64_t seed);
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//==============================================================================
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// API FUNCTIONS
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//==============================================================================
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//==============================================================================
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//! Get OpenMC's master seed.
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//==============================================================================
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extern "C" int64_t openmc_get_seed();
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//==============================================================================
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//! Set OpenMC's master seed.
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//! @param new_seed The master seed. All other seeds will be derived from this
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//! one.
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//==============================================================================
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extern "C" void openmc_set_seed(int64_t new_seed);
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} // namespace openmc
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#endif // OPENMC_RANDOM_LCG_H
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