1 // Copyright (c) 2011 The Chromium Authors. All rights reserved. 2 // Use of this source code is governed by a BSD-style license that can be 3 // found in the LICENSE file. 4 5 #include "base/rand_util.h" 6 7 #include <stddef.h> 8 #include <stdint.h> 9 10 #include <algorithm> 11 #include <limits> 12 #include <memory> 13 14 #include "base/logging.h" 15 #include "base/time/time.h" 16 #include "testing/gtest/include/gtest/gtest.h" 17 18 namespace { 19 20 const int kIntMin = std::numeric_limits<int>::min(); 21 const int kIntMax = std::numeric_limits<int>::max(); 22 23 } // namespace 24 25 TEST(RandUtilTest, RandInt) { 26 EXPECT_EQ(base::RandInt(0, 0), 0); 27 EXPECT_EQ(base::RandInt(kIntMin, kIntMin), kIntMin); 28 EXPECT_EQ(base::RandInt(kIntMax, kIntMax), kIntMax); 29 30 // Check that the DCHECKS in RandInt() don't fire due to internal overflow. 31 // There was a 50% chance of that happening, so calling it 40 times means 32 // the chances of this passing by accident are tiny (9e-13). 33 for (int i = 0; i < 40; ++i) 34 base::RandInt(kIntMin, kIntMax); 35 } 36 37 TEST(RandUtilTest, RandDouble) { 38 // Force 64-bit precision, making sure we're not in a 80-bit FPU register. 39 volatile double number = base::RandDouble(); 40 EXPECT_GT(1.0, number); 41 EXPECT_LE(0.0, number); 42 } 43 44 TEST(RandUtilTest, RandBytes) { 45 const size_t buffer_size = 50; 46 char buffer[buffer_size]; 47 memset(buffer, 0, buffer_size); 48 base::RandBytes(buffer, buffer_size); 49 std::sort(buffer, buffer + buffer_size); 50 // Probability of occurrence of less than 25 unique bytes in 50 random bytes 51 // is below 10^-25. 52 EXPECT_GT(std::unique(buffer, buffer + buffer_size) - buffer, 25); 53 } 54 55 TEST(RandUtilTest, RandBytesAsString) { 56 std::string random_string = base::RandBytesAsString(1); 57 EXPECT_EQ(1U, random_string.size()); 58 random_string = base::RandBytesAsString(145); 59 EXPECT_EQ(145U, random_string.size()); 60 char accumulator = 0; 61 for (size_t i = 0; i < random_string.size(); ++i) 62 accumulator |= random_string[i]; 63 // In theory this test can fail, but it won't before the universe dies of 64 // heat death. 65 EXPECT_NE(0, accumulator); 66 } 67 68 // Make sure that it is still appropriate to use RandGenerator in conjunction 69 // with std::random_shuffle(). 70 TEST(RandUtilTest, RandGeneratorForRandomShuffle) { 71 EXPECT_EQ(base::RandGenerator(1), 0U); 72 EXPECT_LE(std::numeric_limits<ptrdiff_t>::max(), 73 std::numeric_limits<int64_t>::max()); 74 } 75 76 TEST(RandUtilTest, RandGeneratorIsUniform) { 77 // Verify that RandGenerator has a uniform distribution. This is a 78 // regression test that consistently failed when RandGenerator was 79 // implemented this way: 80 // 81 // return base::RandUint64() % max; 82 // 83 // A degenerate case for such an implementation is e.g. a top of 84 // range that is 2/3rds of the way to MAX_UINT64, in which case the 85 // bottom half of the range would be twice as likely to occur as the 86 // top half. A bit of calculus care of jar@ shows that the largest 87 // measurable delta is when the top of the range is 3/4ths of the 88 // way, so that's what we use in the test. 89 const uint64_t kTopOfRange = 90 (std::numeric_limits<uint64_t>::max() / 4ULL) * 3ULL; 91 const uint64_t kExpectedAverage = kTopOfRange / 2ULL; 92 const uint64_t kAllowedVariance = kExpectedAverage / 50ULL; // +/- 2% 93 const int kMinAttempts = 1000; 94 const int kMaxAttempts = 1000000; 95 96 double cumulative_average = 0.0; 97 int count = 0; 98 while (count < kMaxAttempts) { 99 uint64_t value = base::RandGenerator(kTopOfRange); 100 cumulative_average = (count * cumulative_average + value) / (count + 1); 101 102 // Don't quit too quickly for things to start converging, or we may have 103 // a false positive. 104 if (count > kMinAttempts && 105 kExpectedAverage - kAllowedVariance < cumulative_average && 106 cumulative_average < kExpectedAverage + kAllowedVariance) { 107 break; 108 } 109 110 ++count; 111 } 112 113 ASSERT_LT(count, kMaxAttempts) << "Expected average was " << 114 kExpectedAverage << ", average ended at " << cumulative_average; 115 } 116 117 TEST(RandUtilTest, RandUint64ProducesBothValuesOfAllBits) { 118 // This tests to see that our underlying random generator is good 119 // enough, for some value of good enough. 120 uint64_t kAllZeros = 0ULL; 121 uint64_t kAllOnes = ~kAllZeros; 122 uint64_t found_ones = kAllZeros; 123 uint64_t found_zeros = kAllOnes; 124 125 for (size_t i = 0; i < 1000; ++i) { 126 uint64_t value = base::RandUint64(); 127 found_ones |= value; 128 found_zeros &= value; 129 130 if (found_zeros == kAllZeros && found_ones == kAllOnes) 131 return; 132 } 133 134 FAIL() << "Didn't achieve all bit values in maximum number of tries."; 135 } 136 137 // Benchmark test for RandBytes(). Disabled since it's intentionally slow and 138 // does not test anything that isn't already tested by the existing RandBytes() 139 // tests. 140 TEST(RandUtilTest, DISABLED_RandBytesPerf) { 141 // Benchmark the performance of |kTestIterations| of RandBytes() using a 142 // buffer size of |kTestBufferSize|. 143 const int kTestIterations = 10; 144 const size_t kTestBufferSize = 1 * 1024 * 1024; 145 146 std::unique_ptr<uint8_t[]> buffer(new uint8_t[kTestBufferSize]); 147 const base::TimeTicks now = base::TimeTicks::Now(); 148 for (int i = 0; i < kTestIterations; ++i) 149 base::RandBytes(buffer.get(), kTestBufferSize); 150 const base::TimeTicks end = base::TimeTicks::Now(); 151 152 LOG(INFO) << "RandBytes(" << kTestBufferSize << ") took: " 153 << (end - now).InMicroseconds() << "s"; 154 } 155
