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Diffstat (limited to 'third_party/abseil_cpp/absl/random/discrete_distribution.cc')
-rw-r--r-- | third_party/abseil_cpp/absl/random/discrete_distribution.cc | 98 |
1 files changed, 0 insertions, 98 deletions
diff --git a/third_party/abseil_cpp/absl/random/discrete_distribution.cc b/third_party/abseil_cpp/absl/random/discrete_distribution.cc deleted file mode 100644 index 081accee52a4..000000000000 --- a/third_party/abseil_cpp/absl/random/discrete_distribution.cc +++ /dev/null @@ -1,98 +0,0 @@ -// Copyright 2017 The Abseil Authors. -// -// 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 -// -// https://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. - -#include "absl/random/discrete_distribution.h" - -namespace absl { -ABSL_NAMESPACE_BEGIN -namespace random_internal { - -// Initializes the distribution table for Walker's Aliasing algorithm, described -// in Knuth, Vol 2. as well as in https://en.wikipedia.org/wiki/Alias_method -std::vector<std::pair<double, size_t>> InitDiscreteDistribution( - std::vector<double>* probabilities) { - // The empty-case should already be handled by the constructor. - assert(probabilities); - assert(!probabilities->empty()); - - // Step 1. Normalize the input probabilities to 1.0. - double sum = std::accumulate(std::begin(*probabilities), - std::end(*probabilities), 0.0); - if (std::fabs(sum - 1.0) > 1e-6) { - // Scale `probabilities` only when the sum is too far from 1.0. Scaling - // unconditionally will alter the probabilities slightly. - for (double& item : *probabilities) { - item = item / sum; - } - } - - // Step 2. At this point `probabilities` is set to the conditional - // probabilities of each element which sum to 1.0, to within reasonable error. - // These values are used to construct the proportional probability tables for - // the selection phases of Walker's Aliasing algorithm. - // - // To construct the table, pick an element which is under-full (i.e., an - // element for which `(*probabilities)[i] < 1.0/n`), and pair it with an - // element which is over-full (i.e., an element for which - // `(*probabilities)[i] > 1.0/n`). The smaller value can always be retired. - // The larger may still be greater than 1.0/n, or may now be less than 1.0/n, - // and put back onto the appropriate collection. - const size_t n = probabilities->size(); - std::vector<std::pair<double, size_t>> q; - q.reserve(n); - - std::vector<size_t> over; - std::vector<size_t> under; - size_t idx = 0; - for (const double item : *probabilities) { - assert(item >= 0); - const double v = item * n; - q.emplace_back(v, 0); - if (v < 1.0) { - under.push_back(idx++); - } else { - over.push_back(idx++); - } - } - while (!over.empty() && !under.empty()) { - auto lo = under.back(); - under.pop_back(); - auto hi = over.back(); - over.pop_back(); - - q[lo].second = hi; - const double r = q[hi].first - (1.0 - q[lo].first); - q[hi].first = r; - if (r < 1.0) { - under.push_back(hi); - } else { - over.push_back(hi); - } - } - - // Due to rounding errors, there may be un-paired elements in either - // collection; these should all be values near 1.0. For these values, set `q` - // to 1.0 and set the alternate to the identity. - for (auto i : over) { - q[i] = {1.0, i}; - } - for (auto i : under) { - q[i] = {1.0, i}; - } - return q; -} - -} // namespace random_internal -ABSL_NAMESPACE_END -} // namespace absl |