Source code
Revision control
Copy as Markdown
Other Tools
// 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
//
//
// 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 <cinttypes>
#include <random>
#include <sstream>
#include <vector>
#include "gtest/gtest.h"
#include "absl/random/random.h"
template <typename T>
void Use(T) {}
TEST(Examples, Basic) {
absl::BitGen gen;
std::vector<int> objs = {10, 20, 30, 40, 50};
// Choose an element from a set.
auto elem = objs[absl::Uniform(gen, 0u, objs.size())];
Use(elem);
// Generate a uniform value between 1 and 6.
auto dice_roll = absl::Uniform<int>(absl::IntervalClosedClosed, gen, 1, 6);
Use(dice_roll);
// Generate a random byte.
auto byte = absl::Uniform<uint8_t>(gen);
Use(byte);
// Generate a fractional value from [0f, 1f).
auto fraction = absl::Uniform<float>(gen, 0, 1);
Use(fraction);
// Toss a fair coin; 50/50 probability.
bool coin_toss = absl::Bernoulli(gen, 0.5);
Use(coin_toss);
// Select a file size between 1k and 10MB, biased towards smaller file sizes.
auto file_size = absl::LogUniform<size_t>(gen, 1000, 10 * 1000 * 1000);
Use(file_size);
// Randomize (shuffle) a collection.
std::shuffle(std::begin(objs), std::end(objs), gen);
}
TEST(Examples, CreateingCorrelatedVariateSequences) {
// Unexpected PRNG correlation is often a source of bugs,
// so when using absl::BitGen it must be an intentional choice.
// NOTE: All of these only exhibit process-level stability.
// Create a correlated sequence from system entropy.
{
auto my_seed = absl::MakeSeedSeq();
absl::BitGen gen_1(my_seed);
absl::BitGen gen_2(my_seed); // Produces same variates as gen_1.
EXPECT_EQ(absl::Bernoulli(gen_1, 0.5), absl::Bernoulli(gen_2, 0.5));
EXPECT_EQ(absl::Uniform<uint32_t>(gen_1), absl::Uniform<uint32_t>(gen_2));
}
// Create a correlated sequence from an existing URBG.
{
absl::BitGen gen;
auto my_seed = absl::CreateSeedSeqFrom(&gen);
absl::BitGen gen_1(my_seed);
absl::BitGen gen_2(my_seed);
EXPECT_EQ(absl::Bernoulli(gen_1, 0.5), absl::Bernoulli(gen_2, 0.5));
EXPECT_EQ(absl::Uniform<uint32_t>(gen_1), absl::Uniform<uint32_t>(gen_2));
}
// An alternate construction which uses user-supplied data
// instead of a random seed.
{
const char kData[] = "A simple seed string";
std::seed_seq my_seed(std::begin(kData), std::end(kData));
absl::BitGen gen_1(my_seed);
absl::BitGen gen_2(my_seed);
EXPECT_EQ(absl::Bernoulli(gen_1, 0.5), absl::Bernoulli(gen_2, 0.5));
EXPECT_EQ(absl::Uniform<uint32_t>(gen_1), absl::Uniform<uint32_t>(gen_2));
}
}