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 <algorithm> 8 #include <limits> 9 10 #include "base/logging.h" 11 #include "base/memory/scoped_ptr.h" 12 #include "base/time/time.h" 13 #include "testing/gtest/include/gtest/gtest.h" 14 15 namespace { 16 17 const int kIntMin = std::numeric_limits<int>::min(); 18 const int kIntMax = std::numeric_limits<int>::max(); 19 20 } // namespace 21 22 TEST(RandUtilTest, SameMinAndMax) { 23 EXPECT_EQ(base::RandInt(0, 0), 0); 24 EXPECT_EQ(base::RandInt(kIntMin, kIntMin), kIntMin); 25 EXPECT_EQ(base::RandInt(kIntMax, kIntMax), kIntMax); 26 } 27 28 TEST(RandUtilTest, RandDouble) { 29 // Force 64-bit precision, making sure we're not in a 80-bit FPU register. 30 volatile double number = base::RandDouble(); 31 EXPECT_GT(1.0, number); 32 EXPECT_LE(0.0, number); 33 } 34 35 TEST(RandUtilTest, RandBytes) { 36 const size_t buffer_size = 50; 37 char buffer[buffer_size]; 38 memset(buffer, 0, buffer_size); 39 base::RandBytes(buffer, buffer_size); 40 std::sort(buffer, buffer + buffer_size); 41 // Probability of occurrence of less than 25 unique bytes in 50 random bytes 42 // is below 10^-25. 43 EXPECT_GT(std::unique(buffer, buffer + buffer_size) - buffer, 25); 44 } 45 46 TEST(RandUtilTest, RandBytesAsString) { 47 std::string random_string = base::RandBytesAsString(1); 48 EXPECT_EQ(1U, random_string.size()); 49 random_string = base::RandBytesAsString(145); 50 EXPECT_EQ(145U, random_string.size()); 51 char accumulator = 0; 52 for (size_t i = 0; i < random_string.size(); ++i) 53 accumulator |= random_string[i]; 54 // In theory this test can fail, but it won't before the universe dies of 55 // heat death. 56 EXPECT_NE(0, accumulator); 57 } 58 59 // Make sure that it is still appropriate to use RandGenerator in conjunction 60 // with std::random_shuffle(). 61 TEST(RandUtilTest, RandGeneratorForRandomShuffle) { 62 EXPECT_EQ(base::RandGenerator(1), 0U); 63 EXPECT_LE(std::numeric_limits<ptrdiff_t>::max(), 64 std::numeric_limits<int64>::max()); 65 } 66 67 TEST(RandUtilTest, RandGeneratorIsUniform) { 68 // Verify that RandGenerator has a uniform distribution. This is a 69 // regression test that consistently failed when RandGenerator was 70 // implemented this way: 71 // 72 // return base::RandUint64() % max; 73 // 74 // A degenerate case for such an implementation is e.g. a top of 75 // range that is 2/3rds of the way to MAX_UINT64, in which case the 76 // bottom half of the range would be twice as likely to occur as the 77 // top half. A bit of calculus care of jar@ shows that the largest 78 // measurable delta is when the top of the range is 3/4ths of the 79 // way, so that's what we use in the test. 80 const uint64 kTopOfRange = (std::numeric_limits<uint64>::max() / 4ULL) * 3ULL; 81 const uint64 kExpectedAverage = kTopOfRange / 2ULL; 82 const uint64 kAllowedVariance = kExpectedAverage / 50ULL; // +/- 2% 83 const int kMinAttempts = 1000; 84 const int kMaxAttempts = 1000000; 85 86 double cumulative_average = 0.0; 87 int count = 0; 88 while (count < kMaxAttempts) { 89 uint64 value = base::RandGenerator(kTopOfRange); 90 cumulative_average = (count * cumulative_average + value) / (count + 1); 91 92 // Don't quit too quickly for things to start converging, or we may have 93 // a false positive. 94 if (count > kMinAttempts && 95 kExpectedAverage - kAllowedVariance < cumulative_average && 96 cumulative_average < kExpectedAverage + kAllowedVariance) { 97 break; 98 } 99 100 ++count; 101 } 102 103 ASSERT_LT(count, kMaxAttempts) << "Expected average was " << 104 kExpectedAverage << ", average ended at " << cumulative_average; 105 } 106 107 TEST(RandUtilTest, RandUint64ProducesBothValuesOfAllBits) { 108 // This tests to see that our underlying random generator is good 109 // enough, for some value of good enough. 110 uint64 kAllZeros = 0ULL; 111 uint64 kAllOnes = ~kAllZeros; 112 uint64 found_ones = kAllZeros; 113 uint64 found_zeros = kAllOnes; 114 115 for (size_t i = 0; i < 1000; ++i) { 116 uint64 value = base::RandUint64(); 117 found_ones |= value; 118 found_zeros &= value; 119 120 if (found_zeros == kAllZeros && found_ones == kAllOnes) 121 return; 122 } 123 124 FAIL() << "Didn't achieve all bit values in maximum number of tries."; 125 } 126 127 // Benchmark test for RandBytes(). Disabled since it's intentionally slow and 128 // does not test anything that isn't already tested by the existing RandBytes() 129 // tests. 130 TEST(RandUtilTest, DISABLED_RandBytesPerf) { 131 // Benchmark the performance of |kTestIterations| of RandBytes() using a 132 // buffer size of |kTestBufferSize|. 133 const int kTestIterations = 10; 134 const size_t kTestBufferSize = 1 * 1024 * 1024; 135 136 scoped_ptr<uint8[]> buffer(new uint8[kTestBufferSize]); 137 const base::TimeTicks now = base::TimeTicks::HighResNow(); 138 for (int i = 0; i < kTestIterations; ++i) 139 base::RandBytes(buffer.get(), kTestBufferSize); 140 const base::TimeTicks end = base::TimeTicks::HighResNow(); 141 142 LOG(INFO) << "RandBytes(" << kTestBufferSize << ") took: " 143 << (end - now).InMicroseconds() << "s"; 144 } 145
