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.
5 #include "base/rand_util.h"
16 #include "base/logging.h"
17 #include "base/time/time.h"
18 #include "testing/gtest/include/gtest/gtest.h"
24 const int kIntMin = std::numeric_limits<int>::min();
25 const int kIntMax = std::numeric_limits<int>::max();
29 TEST(RandUtilTest, RandInt) {
30 EXPECT_EQ(base::RandInt(0, 0), 0);
31 EXPECT_EQ(base::RandInt(kIntMin, kIntMin), kIntMin);
32 EXPECT_EQ(base::RandInt(kIntMax, kIntMax), kIntMax);
34 // Check that the DCHECKS in RandInt() don't fire due to internal overflow.
35 // There was a 50% chance of that happening, so calling it 40 times means
36 // the chances of this passing by accident are tiny (9e-13).
37 for (int i = 0; i < 40; ++i)
38 base::RandInt(kIntMin, kIntMax);
41 TEST(RandUtilTest, RandDouble) {
42 // Force 64-bit precision, making sure we're not in a 80-bit FPU register.
43 volatile double number = base::RandDouble();
44 EXPECT_GT(1.0, number);
45 EXPECT_LE(0.0, number);
48 TEST(RandUtilTest, RandBytes) {
49 const size_t buffer_size = 50;
50 char buffer[buffer_size];
51 memset(buffer, 0, buffer_size);
52 base::RandBytes(buffer, buffer_size);
53 std::sort(buffer, buffer + buffer_size);
54 // Probability of occurrence of less than 25 unique bytes in 50 random bytes
56 EXPECT_GT(std::unique(buffer, buffer + buffer_size) - buffer, 25);
59 // Verify that calling base::RandBytes with an empty buffer doesn't fail.
60 TEST(RandUtilTest, RandBytes0) {
61 base::RandBytes(nullptr, 0);
64 TEST(RandUtilTest, RandBytesAsString) {
65 std::string random_string = base::RandBytesAsString(1);
66 EXPECT_EQ(1U, random_string.size());
67 random_string = base::RandBytesAsString(145);
68 EXPECT_EQ(145U, random_string.size());
70 for (auto i : random_string)
72 // In theory this test can fail, but it won't before the universe dies of
74 EXPECT_NE(0, accumulator);
77 // Make sure that it is still appropriate to use RandGenerator in conjunction
78 // with std::random_shuffle().
79 TEST(RandUtilTest, RandGeneratorForRandomShuffle) {
80 EXPECT_EQ(base::RandGenerator(1), 0U);
81 EXPECT_LE(std::numeric_limits<ptrdiff_t>::max(),
82 std::numeric_limits<int64_t>::max());
85 TEST(RandUtilTest, RandGeneratorIsUniform) {
86 // Verify that RandGenerator has a uniform distribution. This is a
87 // regression test that consistently failed when RandGenerator was
88 // implemented this way:
90 // return base::RandUint64() % max;
92 // A degenerate case for such an implementation is e.g. a top of
93 // range that is 2/3rds of the way to MAX_UINT64, in which case the
94 // bottom half of the range would be twice as likely to occur as the
95 // top half. A bit of calculus care of jar@ shows that the largest
96 // measurable delta is when the top of the range is 3/4ths of the
97 // way, so that's what we use in the test.
98 constexpr uint64_t kTopOfRange =
99 (std::numeric_limits<uint64_t>::max() / 4ULL) * 3ULL;
100 constexpr double kExpectedAverage = static_cast<double>(kTopOfRange / 2);
101 constexpr double kAllowedVariance = kExpectedAverage / 50.0; // +/- 2%
102 constexpr int kMinAttempts = 1000;
103 constexpr int kMaxAttempts = 1000000;
105 double cumulative_average = 0.0;
107 while (count < kMaxAttempts) {
108 uint64_t value = base::RandGenerator(kTopOfRange);
109 cumulative_average = (count * cumulative_average + value) / (count + 1);
111 // Don't quit too quickly for things to start converging, or we may have
113 if (count > kMinAttempts &&
114 kExpectedAverage - kAllowedVariance < cumulative_average &&
115 cumulative_average < kExpectedAverage + kAllowedVariance) {
122 ASSERT_LT(count, kMaxAttempts) << "Expected average was " << kExpectedAverage
123 << ", average ended at " << cumulative_average;
126 TEST(RandUtilTest, RandUint64ProducesBothValuesOfAllBits) {
127 // This tests to see that our underlying random generator is good
128 // enough, for some value of good enough.
129 uint64_t kAllZeros = 0ULL;
130 uint64_t kAllOnes = ~kAllZeros;
131 uint64_t found_ones = kAllZeros;
132 uint64_t found_zeros = kAllOnes;
134 for (size_t i = 0; i < 1000; ++i) {
135 uint64_t value = base::RandUint64();
137 found_zeros &= value;
139 if (found_zeros == kAllZeros && found_ones == kAllOnes)
143 FAIL() << "Didn't achieve all bit values in maximum number of tries.";
146 TEST(RandUtilTest, RandBytesLonger) {
147 // Fuchsia can only retrieve 256 bytes of entropy at a time, so make sure we
148 // handle longer requests than that.
149 std::string random_string0 = base::RandBytesAsString(255);
150 EXPECT_EQ(255u, random_string0.size());
151 std::string random_string1 = base::RandBytesAsString(1023);
152 EXPECT_EQ(1023u, random_string1.size());
153 std::string random_string2 = base::RandBytesAsString(4097);
154 EXPECT_EQ(4097u, random_string2.size());
157 // Benchmark test for RandBytes(). Disabled since it's intentionally slow and
158 // does not test anything that isn't already tested by the existing RandBytes()
160 TEST(RandUtilTest, DISABLED_RandBytesPerf) {
161 // Benchmark the performance of |kTestIterations| of RandBytes() using a
162 // buffer size of |kTestBufferSize|.
163 const int kTestIterations = 10;
164 const size_t kTestBufferSize = 1 * 1024 * 1024;
166 std::unique_ptr<uint8_t[]> buffer(new uint8_t[kTestBufferSize]);
167 const base::TimeTicks now = base::TimeTicks::Now();
168 for (int i = 0; i < kTestIterations; ++i)
169 base::RandBytes(buffer.get(), kTestBufferSize);
170 const base::TimeTicks end = base::TimeTicks::Now();
172 LOG(INFO) << "RandBytes(" << kTestBufferSize
173 << ") took: " << (end - now).InMicroseconds() << "µs";
176 TEST(RandUtilTest, InsecureRandomGeneratorProducesBothValuesOfAllBits) {
177 // This tests to see that our underlying random generator is good
178 // enough, for some value of good enough.
179 uint64_t kAllZeros = 0ULL;
180 uint64_t kAllOnes = ~kAllZeros;
181 uint64_t found_ones = kAllZeros;
182 uint64_t found_zeros = kAllOnes;
184 InsecureRandomGenerator generator;
187 for (size_t i = 0; i < 1000; ++i) {
188 uint64_t value = generator.RandUint64();
190 found_zeros &= value;
192 if (found_zeros == kAllZeros && found_ones == kAllOnes)
196 FAIL() << "Didn't achieve all bit values in maximum number of tries.";
201 constexpr double kXp1Percent = -2.33;
202 constexpr double kXp99Percent = 2.33;
204 double ChiSquaredCriticalValue(double nu, double x_p) {
205 // From "The Art Of Computer Programming" (TAOCP), Volume 2, Section 3.3.1,
206 // Table 1. This is the asymptotic value for nu > 30, up to O(1 / sqrt(nu)).
207 return nu + sqrt(2. * nu) * x_p + 2. / 3. * (x_p * x_p) - 2. / 3.;
210 int ExtractBits(uint64_t value, int from_bit, int num_bits) {
211 return (value >> from_bit) & ((1 << num_bits) - 1);
214 // Performs a Chi-Squared test on a subset of |num_bits| extracted starting from
215 // |from_bit| in the generated value.
217 // See TAOCP, Volume 2, Section 3.3.1, and
218 // https://en.wikipedia.org/wiki/Pearson%27s_chi-squared_test for details.
220 // This is only one of the many, many random number generator test we could do,
221 // but they are cumbersome, as they are typically very slow, and expected to
222 // fail from time to time, due to their probabilistic nature.
224 // The generator we use has however been vetted with the BigCrush test suite
225 // from Marsaglia, so this should suffice as a smoke test that our
226 // implementation is wrong.
227 bool ChiSquaredTest(InsecureRandomGenerator& gen,
231 const int range = 1 << num_bits;
232 CHECK_EQ(static_cast<int>(n % range), 0) << "Makes computations simpler";
233 std::vector<size_t> samples(range, 0);
235 // Count how many samples pf each value are found. All buckets should be
236 // almost equal if the generator is suitably uniformly random.
237 for (size_t i = 0; i < n; i++) {
238 int sample = ExtractBits(gen.RandUint64(), from_bit, num_bits);
239 samples[sample] += 1;
242 // Compute the Chi-Squared statistic, which is:
243 // \Sum_{k=0}^{range-1} \frac{(count - expected)^2}{expected}
244 double chi_squared = 0.;
245 double expected_count = n / range;
246 for (size_t sample_count : samples) {
247 double deviation = sample_count - expected_count;
248 chi_squared += (deviation * deviation) / expected_count;
251 // The generator should produce numbers that are not too far of (chi_squared
252 // lower than a given quantile), but not too close to the ideal distribution
253 // either (chi_squared is too low).
255 // See The Art Of Computer Programming, Volume 2, Section 3.3.1 for details.
256 return chi_squared > ChiSquaredCriticalValue(range - 1, kXp1Percent) &&
257 chi_squared < ChiSquaredCriticalValue(range - 1, kXp99Percent);
262 TEST(RandUtilTest, InsecureRandomGeneratorChiSquared) {
263 constexpr int kIterations = 50;
265 // Specifically test the low bits, which are usually weaker in random number
266 // generators. We don't use them for the 32 bit number generation, but let's
267 // make sure they are still suitable.
268 for (int start_bit : {1, 2, 3, 8, 12, 20, 32, 48, 54}) {
270 for (int i = 0; i < kIterations; i++) {
271 size_t samples = 1 << 16;
272 InsecureRandomGenerator gen;
273 // Fix the seed to make the test non-flaky.
274 gen.SeedForTesting(kIterations + 1);
275 bool pass = ChiSquaredTest(gen, samples, start_bit, 8);
279 // We exclude 1% on each side, so we expect 98% of tests to pass, meaning 98
280 // * kIterations / 100. However this is asymptotic, so add a bit of leeway.
281 int expected_pass_count = (kIterations * 98) / 100;
282 EXPECT_GE(pass_count, expected_pass_count - ((kIterations * 2) / 100))
283 << "For start_bit = " << start_bit;
287 TEST(RandUtilTest, InsecureRandomGeneratorRandDouble) {
288 InsecureRandomGenerator gen;
291 for (int i = 0; i < 1000; i++) {
292 volatile double x = gen.RandDouble();