1 // Copyright 2011 The Chromium Authors
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, RandFloat) {
49 // Force 32-bit precision, making sure we're not in an 80-bit FPU register.
50 volatile float number = base::RandFloat();
51 EXPECT_GT(1.f, number);
52 EXPECT_LE(0.f, number);
55 TEST(RandUtilTest, BitsToOpenEndedUnitInterval) {
56 // Force 64-bit precision, making sure we're not in an 80-bit FPU register.
57 volatile double all_zeros = BitsToOpenEndedUnitInterval(0x0);
58 EXPECT_EQ(0.0, all_zeros);
60 // Force 64-bit precision, making sure we're not in an 80-bit FPU register.
61 volatile double smallest_nonzero = BitsToOpenEndedUnitInterval(0x1);
62 EXPECT_LT(0.0, smallest_nonzero);
64 for (uint64_t i = 0x2; i < 0x10; ++i) {
65 // Force 64-bit precision, making sure we're not in an 80-bit FPU register.
66 volatile double number = BitsToOpenEndedUnitInterval(i);
67 EXPECT_EQ(i * smallest_nonzero, number);
70 // Force 64-bit precision, making sure we're not in an 80-bit FPU register.
71 volatile double all_ones = BitsToOpenEndedUnitInterval(UINT64_MAX);
72 EXPECT_GT(1.0, all_ones);
75 TEST(RandUtilTest, BitsToOpenEndedUnitIntervalF) {
76 // Force 32-bit precision, making sure we're not in an 80-bit FPU register.
77 volatile float all_zeros = BitsToOpenEndedUnitIntervalF(0x0);
78 EXPECT_EQ(0.f, all_zeros);
80 // Force 32-bit precision, making sure we're not in an 80-bit FPU register.
81 volatile float smallest_nonzero = BitsToOpenEndedUnitIntervalF(0x1);
82 EXPECT_LT(0.f, smallest_nonzero);
84 for (uint64_t i = 0x2; i < 0x10; ++i) {
85 // Force 32-bit precision, making sure we're not in an 80-bit FPU register.
86 volatile float number = BitsToOpenEndedUnitIntervalF(i);
87 EXPECT_EQ(i * smallest_nonzero, number);
90 // Force 32-bit precision, making sure we're not in an 80-bit FPU register.
91 volatile float all_ones = BitsToOpenEndedUnitIntervalF(UINT64_MAX);
92 EXPECT_GT(1.f, all_ones);
95 TEST(RandUtilTest, RandBytes) {
96 const size_t buffer_size = 50;
97 char buffer[buffer_size];
98 memset(buffer, 0, buffer_size);
99 base::RandBytes(buffer, buffer_size);
100 std::sort(buffer, buffer + buffer_size);
101 // Probability of occurrence of less than 25 unique bytes in 50 random bytes
103 EXPECT_GT(std::unique(buffer, buffer + buffer_size) - buffer, 25);
106 // Verify that calling base::RandBytes with an empty buffer doesn't fail.
107 TEST(RandUtilTest, RandBytes0) {
108 base::RandBytes(nullptr, 0);
111 TEST(RandUtilTest, RandBytesAsString) {
112 std::string random_string = base::RandBytesAsString(1);
113 EXPECT_EQ(1U, random_string.size());
114 random_string = base::RandBytesAsString(145);
115 EXPECT_EQ(145U, random_string.size());
116 char accumulator = 0;
117 for (auto i : random_string)
119 // In theory this test can fail, but it won't before the universe dies of
121 EXPECT_NE(0, accumulator);
124 // Make sure that it is still appropriate to use RandGenerator in conjunction
125 // with std::random_shuffle().
126 TEST(RandUtilTest, RandGeneratorForRandomShuffle) {
127 EXPECT_EQ(base::RandGenerator(1), 0U);
128 EXPECT_LE(std::numeric_limits<ptrdiff_t>::max(),
129 std::numeric_limits<int64_t>::max());
132 TEST(RandUtilTest, RandGeneratorIsUniform) {
133 // Verify that RandGenerator has a uniform distribution. This is a
134 // regression test that consistently failed when RandGenerator was
135 // implemented this way:
137 // return base::RandUint64() % max;
139 // A degenerate case for such an implementation is e.g. a top of
140 // range that is 2/3rds of the way to MAX_UINT64, in which case the
141 // bottom half of the range would be twice as likely to occur as the
142 // top half. A bit of calculus care of jar@ shows that the largest
143 // measurable delta is when the top of the range is 3/4ths of the
144 // way, so that's what we use in the test.
145 constexpr uint64_t kTopOfRange =
146 (std::numeric_limits<uint64_t>::max() / 4ULL) * 3ULL;
147 constexpr double kExpectedAverage = static_cast<double>(kTopOfRange / 2);
148 constexpr double kAllowedVariance = kExpectedAverage / 50.0; // +/- 2%
149 constexpr int kMinAttempts = 1000;
150 constexpr int kMaxAttempts = 1000000;
152 double cumulative_average = 0.0;
154 while (count < kMaxAttempts) {
155 uint64_t value = base::RandGenerator(kTopOfRange);
156 cumulative_average = (count * cumulative_average + value) / (count + 1);
158 // Don't quit too quickly for things to start converging, or we may have
160 if (count > kMinAttempts &&
161 kExpectedAverage - kAllowedVariance < cumulative_average &&
162 cumulative_average < kExpectedAverage + kAllowedVariance) {
169 ASSERT_LT(count, kMaxAttempts) << "Expected average was " << kExpectedAverage
170 << ", average ended at " << cumulative_average;
173 TEST(RandUtilTest, RandUint64ProducesBothValuesOfAllBits) {
174 // This tests to see that our underlying random generator is good
175 // enough, for some value of good enough.
176 uint64_t kAllZeros = 0ULL;
177 uint64_t kAllOnes = ~kAllZeros;
178 uint64_t found_ones = kAllZeros;
179 uint64_t found_zeros = kAllOnes;
181 for (size_t i = 0; i < 1000; ++i) {
182 uint64_t value = base::RandUint64();
184 found_zeros &= value;
186 if (found_zeros == kAllZeros && found_ones == kAllOnes)
190 FAIL() << "Didn't achieve all bit values in maximum number of tries.";
193 TEST(RandUtilTest, RandBytesLonger) {
194 // Fuchsia can only retrieve 256 bytes of entropy at a time, so make sure we
195 // handle longer requests than that.
196 std::string random_string0 = base::RandBytesAsString(255);
197 EXPECT_EQ(255u, random_string0.size());
198 std::string random_string1 = base::RandBytesAsString(1023);
199 EXPECT_EQ(1023u, random_string1.size());
200 std::string random_string2 = base::RandBytesAsString(4097);
201 EXPECT_EQ(4097u, random_string2.size());
204 // Benchmark test for RandBytes(). Disabled since it's intentionally slow and
205 // does not test anything that isn't already tested by the existing RandBytes()
207 TEST(RandUtilTest, DISABLED_RandBytesPerf) {
208 // Benchmark the performance of |kTestIterations| of RandBytes() using a
209 // buffer size of |kTestBufferSize|.
210 const int kTestIterations = 10;
211 const size_t kTestBufferSize = 1 * 1024 * 1024;
213 std::unique_ptr<uint8_t[]> buffer(new uint8_t[kTestBufferSize]);
214 const base::TimeTicks now = base::TimeTicks::Now();
215 for (int i = 0; i < kTestIterations; ++i)
216 base::RandBytes(buffer.get(), kTestBufferSize);
217 const base::TimeTicks end = base::TimeTicks::Now();
219 LOG(INFO) << "RandBytes(" << kTestBufferSize
220 << ") took: " << (end - now).InMicroseconds() << "µs";
223 TEST(RandUtilTest, InsecureRandomGeneratorProducesBothValuesOfAllBits) {
224 // This tests to see that our underlying random generator is good
225 // enough, for some value of good enough.
226 uint64_t kAllZeros = 0ULL;
227 uint64_t kAllOnes = ~kAllZeros;
228 uint64_t found_ones = kAllZeros;
229 uint64_t found_zeros = kAllOnes;
231 InsecureRandomGenerator generator;
233 for (size_t i = 0; i < 1000; ++i) {
234 uint64_t value = generator.RandUint64();
236 found_zeros &= value;
238 if (found_zeros == kAllZeros && found_ones == kAllOnes)
242 FAIL() << "Didn't achieve all bit values in maximum number of tries.";
247 constexpr double kXp1Percent = -2.33;
248 constexpr double kXp99Percent = 2.33;
250 double ChiSquaredCriticalValue(double nu, double x_p) {
251 // From "The Art Of Computer Programming" (TAOCP), Volume 2, Section 3.3.1,
252 // Table 1. This is the asymptotic value for nu > 30, up to O(1 / sqrt(nu)).
253 return nu + sqrt(2. * nu) * x_p + 2. / 3. * (x_p * x_p) - 2. / 3.;
256 int ExtractBits(uint64_t value, int from_bit, int num_bits) {
257 return (value >> from_bit) & ((1 << num_bits) - 1);
260 // Performs a Chi-Squared test on a subset of |num_bits| extracted starting from
261 // |from_bit| in the generated value.
263 // See TAOCP, Volume 2, Section 3.3.1, and
264 // https://en.wikipedia.org/wiki/Pearson%27s_chi-squared_test for details.
266 // This is only one of the many, many random number generator test we could do,
267 // but they are cumbersome, as they are typically very slow, and expected to
268 // fail from time to time, due to their probabilistic nature.
270 // The generator we use has however been vetted with the BigCrush test suite
271 // from Marsaglia, so this should suffice as a smoke test that our
272 // implementation is wrong.
273 bool ChiSquaredTest(InsecureRandomGenerator& gen,
277 const int range = 1 << num_bits;
278 CHECK_EQ(static_cast<int>(n % range), 0) << "Makes computations simpler";
279 std::vector<size_t> samples(range, 0);
281 // Count how many samples pf each value are found. All buckets should be
282 // almost equal if the generator is suitably uniformly random.
283 for (size_t i = 0; i < n; i++) {
284 int sample = ExtractBits(gen.RandUint64(), from_bit, num_bits);
285 samples[sample] += 1;
288 // Compute the Chi-Squared statistic, which is:
289 // \Sum_{k=0}^{range-1} \frac{(count - expected)^2}{expected}
290 double chi_squared = 0.;
291 double expected_count = n / range;
292 for (size_t sample_count : samples) {
293 double deviation = sample_count - expected_count;
294 chi_squared += (deviation * deviation) / expected_count;
297 // The generator should produce numbers that are not too far of (chi_squared
298 // lower than a given quantile), but not too close to the ideal distribution
299 // either (chi_squared is too low).
301 // See The Art Of Computer Programming, Volume 2, Section 3.3.1 for details.
302 return chi_squared > ChiSquaredCriticalValue(range - 1, kXp1Percent) &&
303 chi_squared < ChiSquaredCriticalValue(range - 1, kXp99Percent);
308 TEST(RandUtilTest, InsecureRandomGeneratorChiSquared) {
309 constexpr int kIterations = 50;
311 // Specifically test the low bits, which are usually weaker in random number
312 // generators. We don't use them for the 32 bit number generation, but let's
313 // make sure they are still suitable.
314 for (int start_bit : {1, 2, 3, 8, 12, 20, 32, 48, 54}) {
316 for (int i = 0; i < kIterations; i++) {
317 size_t samples = 1 << 16;
318 InsecureRandomGenerator gen;
319 // Fix the seed to make the test non-flaky.
320 gen.ReseedForTesting(kIterations + 1);
321 bool pass = ChiSquaredTest(gen, samples, start_bit, 8);
325 // We exclude 1% on each side, so we expect 98% of tests to pass, meaning 98
326 // * kIterations / 100. However this is asymptotic, so add a bit of leeway.
327 int expected_pass_count = (kIterations * 98) / 100;
328 EXPECT_GE(pass_count, expected_pass_count - ((kIterations * 2) / 100))
329 << "For start_bit = " << start_bit;
333 TEST(RandUtilTest, InsecureRandomGeneratorRandDouble) {
334 InsecureRandomGenerator gen;
336 for (int i = 0; i < 1000; i++) {
337 volatile double x = gen.RandDouble();