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/*
* PCG Random Number Generation for C.
*
* Copyright 2014 Melissa O'Neill <oneill@pcg-random.org>
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*
* For additional information about the PCG random number generation scheme,
* including its license and other licensing options, visit
*
* http://www.pcg-random.org
*/
/*
* This code is derived from the canonical C++ PCG implementation, which
* has many additional features and is preferable if you can use C++ in
* your project.
*
* Repetative C code is derived using C preprocessor metaprogramming
* techniques.
*/
#include "pcg_variants.h"
/* Multi-step advance functions (jump-ahead, jump-back)
*
* The method used here is based on Brown, "Random Number Generation
* with Arbitrary Stride,", Transactions of the American Nuclear
* Society (Nov. 1994). The algorithm is very similar to fast
* exponentiation.
*
* Even though delta is an unsigned integer, we can pass a
* signed integer to go backwards, it just goes "the long way round".
*/
uint16_t pcg_advance_lcg_16(uint16_t state, uint16_t delta, uint16_t cur_mult,
uint16_t cur_plus)
{
uint16_t acc_mult = 1u;
uint16_t acc_plus = 0u;
while (delta > 0) {
if (delta & 1) {
acc_mult *= cur_mult;
acc_plus = acc_plus * cur_mult + cur_plus;
}
cur_plus = (cur_mult + 1) * cur_plus;
cur_mult *= cur_mult;
delta /= 2;
}
return acc_mult * state + acc_plus;
}
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