examples_test.cc (3091B)
1 // Copyright 2017 The Abseil Authors. 2 // 3 // Licensed under the Apache License, Version 2.0 (the "License"); 4 // you may not use this file except in compliance with the License. 5 // You may obtain a copy of the License at 6 // 7 // https://www.apache.org/licenses/LICENSE-2.0 8 // 9 // Unless required by applicable law or agreed to in writing, software 10 // distributed under the License is distributed on an "AS IS" BASIS, 11 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 12 // See the License for the specific language governing permissions and 13 // limitations under the License. 14 15 #include <cinttypes> 16 #include <random> 17 #include <sstream> 18 #include <vector> 19 20 #include "gtest/gtest.h" 21 #include "absl/random/random.h" 22 23 template <typename T> 24 void Use(T) {} 25 26 TEST(Examples, Basic) { 27 absl::BitGen gen; 28 std::vector<int> objs = {10, 20, 30, 40, 50}; 29 30 // Choose an element from a set. 31 auto elem = objs[absl::Uniform(gen, 0u, objs.size())]; 32 Use(elem); 33 34 // Generate a uniform value between 1 and 6. 35 auto dice_roll = absl::Uniform<int>(absl::IntervalClosedClosed, gen, 1, 6); 36 Use(dice_roll); 37 38 // Generate a random byte. 39 auto byte = absl::Uniform<uint8_t>(gen); 40 Use(byte); 41 42 // Generate a fractional value from [0f, 1f). 43 auto fraction = absl::Uniform<float>(gen, 0, 1); 44 Use(fraction); 45 46 // Toss a fair coin; 50/50 probability. 47 bool coin_toss = absl::Bernoulli(gen, 0.5); 48 Use(coin_toss); 49 50 // Select a file size between 1k and 10MB, biased towards smaller file sizes. 51 auto file_size = absl::LogUniform<size_t>(gen, 1000, 10 * 1000 * 1000); 52 Use(file_size); 53 54 // Randomize (shuffle) a collection. 55 std::shuffle(std::begin(objs), std::end(objs), gen); 56 } 57 58 TEST(Examples, CreateingCorrelatedVariateSequences) { 59 // Unexpected PRNG correlation is often a source of bugs, 60 // so when using absl::BitGen it must be an intentional choice. 61 // NOTE: All of these only exhibit process-level stability. 62 63 // Create a correlated sequence from system entropy. 64 { 65 auto my_seed = absl::MakeSeedSeq(); 66 67 absl::BitGen gen_1(my_seed); 68 absl::BitGen gen_2(my_seed); // Produces same variates as gen_1. 69 70 EXPECT_EQ(absl::Bernoulli(gen_1, 0.5), absl::Bernoulli(gen_2, 0.5)); 71 EXPECT_EQ(absl::Uniform<uint32_t>(gen_1), absl::Uniform<uint32_t>(gen_2)); 72 } 73 74 // Create a correlated sequence from an existing URBG. 75 { 76 absl::BitGen gen; 77 78 auto my_seed = absl::CreateSeedSeqFrom(&gen); 79 absl::BitGen gen_1(my_seed); 80 absl::BitGen gen_2(my_seed); 81 82 EXPECT_EQ(absl::Bernoulli(gen_1, 0.5), absl::Bernoulli(gen_2, 0.5)); 83 EXPECT_EQ(absl::Uniform<uint32_t>(gen_1), absl::Uniform<uint32_t>(gen_2)); 84 } 85 86 // An alternate construction which uses user-supplied data 87 // instead of a random seed. 88 { 89 const char kData[] = "A simple seed string"; 90 std::seed_seq my_seed(std::begin(kData), std::end(kData)); 91 92 absl::BitGen gen_1(my_seed); 93 absl::BitGen gen_2(my_seed); 94 95 EXPECT_EQ(absl::Bernoulli(gen_1, 0.5), absl::Bernoulli(gen_2, 0.5)); 96 EXPECT_EQ(absl::Uniform<uint32_t>(gen_1), absl::Uniform<uint32_t>(gen_2)); 97 } 98 }