fc8dc48020
git-subtree-dir: third_party/abseil_cpp git-subtree-mainline:ffb2ae54begit-subtree-split:768eb2ca28
99 lines
3 KiB
C++
99 lines
3 KiB
C++
// Copyright 2017 The Abseil Authors.
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// https://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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#include <cinttypes>
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#include <random>
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#include <sstream>
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#include <vector>
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#include "gtest/gtest.h"
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#include "absl/random/random.h"
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template <typename T>
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void Use(T) {}
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TEST(Examples, Basic) {
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absl::BitGen gen;
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std::vector<int> objs = {10, 20, 30, 40, 50};
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// Choose an element from a set.
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auto elem = objs[absl::Uniform(gen, 0u, objs.size())];
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Use(elem);
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// Generate a uniform value between 1 and 6.
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auto dice_roll = absl::Uniform<int>(absl::IntervalClosedClosed, gen, 1, 6);
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Use(dice_roll);
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// Generate a random byte.
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auto byte = absl::Uniform<uint8_t>(gen);
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Use(byte);
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// Generate a fractional value from [0f, 1f).
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auto fraction = absl::Uniform<float>(gen, 0, 1);
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Use(fraction);
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// Toss a fair coin; 50/50 probability.
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bool coin_toss = absl::Bernoulli(gen, 0.5);
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Use(coin_toss);
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// Select a file size between 1k and 10MB, biased towards smaller file sizes.
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auto file_size = absl::LogUniform<size_t>(gen, 1000, 10 * 1000 * 1000);
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Use(file_size);
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// Randomize (shuffle) a collection.
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std::shuffle(std::begin(objs), std::end(objs), gen);
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}
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TEST(Examples, CreateingCorrelatedVariateSequences) {
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// Unexpected PRNG correlation is often a source of bugs,
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// so when using absl::BitGen it must be an intentional choice.
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// NOTE: All of these only exhibit process-level stability.
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// Create a correlated sequence from system entropy.
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{
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auto my_seed = absl::MakeSeedSeq();
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absl::BitGen gen_1(my_seed);
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absl::BitGen gen_2(my_seed); // Produces same variates as gen_1.
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EXPECT_EQ(absl::Bernoulli(gen_1, 0.5), absl::Bernoulli(gen_2, 0.5));
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EXPECT_EQ(absl::Uniform<uint32_t>(gen_1), absl::Uniform<uint32_t>(gen_2));
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}
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// Create a correlated sequence from an existing URBG.
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{
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absl::BitGen gen;
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auto my_seed = absl::CreateSeedSeqFrom(&gen);
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absl::BitGen gen_1(my_seed);
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absl::BitGen gen_2(my_seed);
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EXPECT_EQ(absl::Bernoulli(gen_1, 0.5), absl::Bernoulli(gen_2, 0.5));
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EXPECT_EQ(absl::Uniform<uint32_t>(gen_1), absl::Uniform<uint32_t>(gen_2));
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}
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// An alternate construction which uses user-supplied data
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// instead of a random seed.
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{
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const char kData[] = "A simple seed string";
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std::seed_seq my_seed(std::begin(kData), std::end(kData));
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absl::BitGen gen_1(my_seed);
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absl::BitGen gen_2(my_seed);
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EXPECT_EQ(absl::Bernoulli(gen_1, 0.5), absl::Bernoulli(gen_2, 0.5));
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EXPECT_EQ(absl::Uniform<uint32_t>(gen_1), absl::Uniform<uint32_t>(gen_2));
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}
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}
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