mirror of https://github.com/oxen-io/oxen-core.git
77 lines
3.4 KiB
C++
77 lines
3.4 KiB
C++
// Copyright (c) 2019, The Loki Project
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//
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// All rights reserved.
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//
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// Redistribution and use in source and binary forms, with or without modification, are
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// permitted provided that the following conditions are met:
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//
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// 1. Redistributions of source code must retain the above copyright notice, this list of
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// conditions and the following disclaimer.
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//
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// 2. Redistributions in binary form must reproduce the above copyright notice, this list
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// of conditions and the following disclaimer in the documentation and/or other
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// materials provided with the distribution.
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//
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// 3. Neither the name of the copyright holder nor the names of its contributors may be
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// used to endorse or promote products derived from this software without specific
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// prior written permission.
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//
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// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY
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// EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
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// MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL
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// THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
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// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
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// PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
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// INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
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// STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF
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// THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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#pragma once
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#include <random>
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namespace tools {
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/// A thread-local, pre-seeded mt19937_64 rng ready for use. Don't use this where an RNG with a
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/// specific seed is needed.
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extern thread_local std::mt19937_64 rng;
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/// Generates a deterministic uint64_t uniformly distributed over [0, n). This is roughly
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/// equivalent to `std::uniform_int_distribution<uint64_t>{0, n}(rng)`, but that is not guaranteed
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/// to be unique across platforms/compilers, while this is.
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uint64_t uniform_distribution_portable(std::mt19937_64& rng, uint64_t n);
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/// Uniformly shuffles all the elements in [begin, end) in a deterministic method so that, given the
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/// same seed, this will always produce the same result on any platform/compiler/etc.
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template <typename RandomIt>
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void shuffle_portable(RandomIt begin, RandomIt end, std::mt19937_64& rng) {
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if (end <= begin + 1)
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return;
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const size_t size = std::distance(begin, end);
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for (size_t i = 1; i < size; i++) {
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size_t j = (size_t)uniform_distribution_portable(rng, i + 1);
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using std::swap;
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swap(begin[i], begin[j]);
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}
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}
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/// Returns a random element between the elements in [begin, end) will use the random number
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/// generator provided as g
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template <typename Iter, typename RandomGenerator>
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Iter select_randomly(Iter begin, Iter end, RandomGenerator& g) {
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auto dist = std::distance(begin, end);
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if (dist <= 1)
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return begin; // Handles both begin=end case and single-element case
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std::advance(begin, std::uniform_int_distribution<>{0, static_cast<int>(dist - 1)}(g));
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return begin;
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}
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/// Returns a random element same as above but defaults to the seeded random number generator
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/// defined in this file
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template <typename Iter>
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Iter select_randomly(Iter begin, Iter end) {
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return select_randomly(begin, end, rng);
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}
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}; // namespace tools
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