Abdelrahman Said
60 lines
2.0 KiB
C
60 lines
2.0 KiB
C
/*
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* PCG Random Number Generation for C.
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*
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* Copyright 2014-2019 Melissa O'Neill <oneill@pcg-random.org>,
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* and the PCG Project contributors.
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*
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* SPDX-License-Identifier: (Apache-2.0 OR MIT)
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*
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* Licensed under the Apache License, Version 2.0 (provided in
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* LICENSE-APACHE.txt and at http://www.apache.org/licenses/LICENSE-2.0)
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* or under the MIT license (provided in LICENSE-MIT.txt and at
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* http://opensource.org/licenses/MIT), at your option. This file may not
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* be copied, modified, or distributed except according to those terms.
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*
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* Distributed on an "AS IS" BASIS, WITHOUT WARRANTY OF ANY KIND, either
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* express or implied. See your chosen license for details.
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*
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* For additional information about the PCG random number generation scheme,
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* visit http://www.pcg-random.org/.
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*/
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/*
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* This code is derived from the canonical C++ PCG implementation, which
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* has many additional features and is preferable if you can use C++ in
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* your project.
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*
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* Repetative C code is derived using C preprocessor metaprogramming
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* techniques.
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*/
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#include "pcg_variants.h"
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/* Multi-step advance functions (jump-ahead, jump-back)
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*
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* The method used here is based on Brown, "Random Number Generation
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* with Arbitrary Stride,", Transactions of the American Nuclear
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* Society (Nov. 1994). The algorithm is very similar to fast
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* exponentiation.
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*
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* Even though delta is an unsigned integer, we can pass a
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* signed integer to go backwards, it just goes "the long way round".
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*/
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uint64_t pcg_advance_lcg_64(uint64_t state, uint64_t delta, uint64_t cur_mult,
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uint64_t cur_plus)
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{
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uint64_t acc_mult = 1u;
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uint64_t acc_plus = 0u;
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while (delta > 0) {
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if (delta & 1) {
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acc_mult *= cur_mult;
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acc_plus = acc_plus * cur_mult + cur_plus;
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}
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cur_plus = (cur_mult + 1) * cur_plus;
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cur_mult *= cur_mult;
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delta /= 2;
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}
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return acc_mult * state + acc_plus;
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}
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