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, RandTimeDelta) {
58 base::RandTimeDelta(-base::Seconds(2), -base::Seconds(1));
59 EXPECT_GE(delta, -base::Seconds(2));
60 EXPECT_LT(delta, -base::Seconds(1));
64 const auto delta = base::RandTimeDelta(-base::Seconds(2), base::Seconds(2));
65 EXPECT_GE(delta, -base::Seconds(2));
66 EXPECT_LT(delta, base::Seconds(2));
70 const auto delta = base::RandTimeDelta(base::Seconds(1), base::Seconds(2));
71 EXPECT_GE(delta, base::Seconds(1));
72 EXPECT_LT(delta, base::Seconds(2));
76 TEST(RandUtilTest, RandTimeDeltaUpTo) {
77 const auto delta = base::RandTimeDeltaUpTo(base::Seconds(2));
78 EXPECT_FALSE(delta.is_negative());
79 EXPECT_LT(delta, base::Seconds(2));
82 TEST(RandUtilTest, BitsToOpenEndedUnitInterval) {
83 // Force 64-bit precision, making sure we're not in an 80-bit FPU register.
84 volatile double all_zeros = BitsToOpenEndedUnitInterval(0x0);
85 EXPECT_EQ(0.0, all_zeros);
87 // Force 64-bit precision, making sure we're not in an 80-bit FPU register.
88 volatile double smallest_nonzero = BitsToOpenEndedUnitInterval(0x1);
89 EXPECT_LT(0.0, smallest_nonzero);
91 for (uint64_t i = 0x2; i < 0x10; ++i) {
92 // Force 64-bit precision, making sure we're not in an 80-bit FPU register.
93 volatile double number = BitsToOpenEndedUnitInterval(i);
94 EXPECT_EQ(i * smallest_nonzero, number);
97 // Force 64-bit precision, making sure we're not in an 80-bit FPU register.
98 volatile double all_ones = BitsToOpenEndedUnitInterval(UINT64_MAX);
99 EXPECT_GT(1.0, all_ones);
102 TEST(RandUtilTest, BitsToOpenEndedUnitIntervalF) {
103 // Force 32-bit precision, making sure we're not in an 80-bit FPU register.
104 volatile float all_zeros = BitsToOpenEndedUnitIntervalF(0x0);
105 EXPECT_EQ(0.f, all_zeros);
107 // Force 32-bit precision, making sure we're not in an 80-bit FPU register.
108 volatile float smallest_nonzero = BitsToOpenEndedUnitIntervalF(0x1);
109 EXPECT_LT(0.f, smallest_nonzero);
111 for (uint64_t i = 0x2; i < 0x10; ++i) {
112 // Force 32-bit precision, making sure we're not in an 80-bit FPU register.
113 volatile float number = BitsToOpenEndedUnitIntervalF(i);
114 EXPECT_EQ(i * smallest_nonzero, number);
117 // Force 32-bit precision, making sure we're not in an 80-bit FPU register.
118 volatile float all_ones = BitsToOpenEndedUnitIntervalF(UINT64_MAX);
119 EXPECT_GT(1.f, all_ones);
122 TEST(RandUtilTest, RandBytes) {
123 const size_t buffer_size = 50;
124 char buffer[buffer_size];
125 memset(buffer, 0, buffer_size);
126 base::RandBytes(buffer, buffer_size);
127 std::sort(buffer, buffer + buffer_size);
128 // Probability of occurrence of less than 25 unique bytes in 50 random bytes
130 EXPECT_GT(std::unique(buffer, buffer + buffer_size) - buffer, 25);
133 // Verify that calling base::RandBytes with an empty buffer doesn't fail.
134 TEST(RandUtilTest, RandBytes0) {
135 base::RandBytes(nullptr, 0);
138 TEST(RandUtilTest, RandBytesAsString) {
139 std::string random_string = base::RandBytesAsString(1);
140 EXPECT_EQ(1U, random_string.size());
141 random_string = base::RandBytesAsString(145);
142 EXPECT_EQ(145U, random_string.size());
143 char accumulator = 0;
144 for (auto i : random_string)
146 // In theory this test can fail, but it won't before the universe dies of
148 EXPECT_NE(0, accumulator);
151 // Make sure that it is still appropriate to use RandGenerator in conjunction
152 // with std::random_shuffle().
153 TEST(RandUtilTest, RandGeneratorForRandomShuffle) {
154 EXPECT_EQ(base::RandGenerator(1), 0U);
155 EXPECT_LE(std::numeric_limits<ptrdiff_t>::max(),
156 std::numeric_limits<int64_t>::max());
159 TEST(RandUtilTest, RandGeneratorIsUniform) {
160 // Verify that RandGenerator has a uniform distribution. This is a
161 // regression test that consistently failed when RandGenerator was
162 // implemented this way:
164 // return base::RandUint64() % max;
166 // A degenerate case for such an implementation is e.g. a top of
167 // range that is 2/3rds of the way to MAX_UINT64, in which case the
168 // bottom half of the range would be twice as likely to occur as the
169 // top half. A bit of calculus care of jar@ shows that the largest
170 // measurable delta is when the top of the range is 3/4ths of the
171 // way, so that's what we use in the test.
172 constexpr uint64_t kTopOfRange =
173 (std::numeric_limits<uint64_t>::max() / 4ULL) * 3ULL;
174 constexpr double kExpectedAverage = static_cast<double>(kTopOfRange / 2);
175 constexpr double kAllowedVariance = kExpectedAverage / 50.0; // +/- 2%
176 constexpr int kMinAttempts = 1000;
177 constexpr int kMaxAttempts = 1000000;
179 double cumulative_average = 0.0;
181 while (count < kMaxAttempts) {
182 uint64_t value = base::RandGenerator(kTopOfRange);
183 cumulative_average = (count * cumulative_average + value) / (count + 1);
185 // Don't quit too quickly for things to start converging, or we may have
187 if (count > kMinAttempts &&
188 kExpectedAverage - kAllowedVariance < cumulative_average &&
189 cumulative_average < kExpectedAverage + kAllowedVariance) {
196 ASSERT_LT(count, kMaxAttempts) << "Expected average was " << kExpectedAverage
197 << ", average ended at " << cumulative_average;
200 TEST(RandUtilTest, RandUint64ProducesBothValuesOfAllBits) {
201 // This tests to see that our underlying random generator is good
202 // enough, for some value of good enough.
203 uint64_t kAllZeros = 0ULL;
204 uint64_t kAllOnes = ~kAllZeros;
205 uint64_t found_ones = kAllZeros;
206 uint64_t found_zeros = kAllOnes;
208 for (size_t i = 0; i < 1000; ++i) {
209 uint64_t value = base::RandUint64();
211 found_zeros &= value;
213 if (found_zeros == kAllZeros && found_ones == kAllOnes)
217 FAIL() << "Didn't achieve all bit values in maximum number of tries.";
220 TEST(RandUtilTest, RandBytesLonger) {
221 // Fuchsia can only retrieve 256 bytes of entropy at a time, so make sure we
222 // handle longer requests than that.
223 std::string random_string0 = base::RandBytesAsString(255);
224 EXPECT_EQ(255u, random_string0.size());
225 std::string random_string1 = base::RandBytesAsString(1023);
226 EXPECT_EQ(1023u, random_string1.size());
227 std::string random_string2 = base::RandBytesAsString(4097);
228 EXPECT_EQ(4097u, random_string2.size());
231 // Benchmark test for RandBytes(). Disabled since it's intentionally slow and
232 // does not test anything that isn't already tested by the existing RandBytes()
234 TEST(RandUtilTest, DISABLED_RandBytesPerf) {
235 // Benchmark the performance of |kTestIterations| of RandBytes() using a
236 // buffer size of |kTestBufferSize|.
237 const int kTestIterations = 10;
238 const size_t kTestBufferSize = 1 * 1024 * 1024;
240 std::unique_ptr<uint8_t[]> buffer(new uint8_t[kTestBufferSize]);
241 const base::TimeTicks now = base::TimeTicks::Now();
242 for (int i = 0; i < kTestIterations; ++i)
243 base::RandBytes(buffer.get(), kTestBufferSize);
244 const base::TimeTicks end = base::TimeTicks::Now();
246 LOG(INFO) << "RandBytes(" << kTestBufferSize
247 << ") took: " << (end - now).InMicroseconds() << "µs";
250 TEST(RandUtilTest, InsecureRandomGeneratorProducesBothValuesOfAllBits) {
251 // This tests to see that our underlying random generator is good
252 // enough, for some value of good enough.
253 uint64_t kAllZeros = 0ULL;
254 uint64_t kAllOnes = ~kAllZeros;
255 uint64_t found_ones = kAllZeros;
256 uint64_t found_zeros = kAllOnes;
258 InsecureRandomGenerator generator;
260 for (size_t i = 0; i < 1000; ++i) {
261 uint64_t value = generator.RandUint64();
263 found_zeros &= value;
265 if (found_zeros == kAllZeros && found_ones == kAllOnes)
269 FAIL() << "Didn't achieve all bit values in maximum number of tries.";
274 constexpr double kXp1Percent = -2.33;
275 constexpr double kXp99Percent = 2.33;
277 double ChiSquaredCriticalValue(double nu, double x_p) {
278 // From "The Art Of Computer Programming" (TAOCP), Volume 2, Section 3.3.1,
279 // Table 1. This is the asymptotic value for nu > 30, up to O(1 / sqrt(nu)).
280 return nu + sqrt(2. * nu) * x_p + 2. / 3. * (x_p * x_p) - 2. / 3.;
283 int ExtractBits(uint64_t value, int from_bit, int num_bits) {
284 return (value >> from_bit) & ((1 << num_bits) - 1);
287 // Performs a Chi-Squared test on a subset of |num_bits| extracted starting from
288 // |from_bit| in the generated value.
290 // See TAOCP, Volume 2, Section 3.3.1, and
291 // https://en.wikipedia.org/wiki/Pearson%27s_chi-squared_test for details.
293 // This is only one of the many, many random number generator test we could do,
294 // but they are cumbersome, as they are typically very slow, and expected to
295 // fail from time to time, due to their probabilistic nature.
297 // The generator we use has however been vetted with the BigCrush test suite
298 // from Marsaglia, so this should suffice as a smoke test that our
299 // implementation is wrong.
300 bool ChiSquaredTest(InsecureRandomGenerator& gen,
304 const int range = 1 << num_bits;
305 CHECK_EQ(static_cast<int>(n % range), 0) << "Makes computations simpler";
306 std::vector<size_t> samples(range, 0);
308 // Count how many samples pf each value are found. All buckets should be
309 // almost equal if the generator is suitably uniformly random.
310 for (size_t i = 0; i < n; i++) {
311 int sample = ExtractBits(gen.RandUint64(), from_bit, num_bits);
312 samples[sample] += 1;
315 // Compute the Chi-Squared statistic, which is:
316 // \Sum_{k=0}^{range-1} \frac{(count - expected)^2}{expected}
317 double chi_squared = 0.;
318 double expected_count = n / range;
319 for (size_t sample_count : samples) {
320 double deviation = sample_count - expected_count;
321 chi_squared += (deviation * deviation) / expected_count;
324 // The generator should produce numbers that are not too far of (chi_squared
325 // lower than a given quantile), but not too close to the ideal distribution
326 // either (chi_squared is too low).
328 // See The Art Of Computer Programming, Volume 2, Section 3.3.1 for details.
329 return chi_squared > ChiSquaredCriticalValue(range - 1, kXp1Percent) &&
330 chi_squared < ChiSquaredCriticalValue(range - 1, kXp99Percent);
335 TEST(RandUtilTest, InsecureRandomGeneratorChiSquared) {
336 constexpr int kIterations = 50;
338 // Specifically test the low bits, which are usually weaker in random number
339 // generators. We don't use them for the 32 bit number generation, but let's
340 // make sure they are still suitable.
341 for (int start_bit : {1, 2, 3, 8, 12, 20, 32, 48, 54}) {
343 for (int i = 0; i < kIterations; i++) {
344 size_t samples = 1 << 16;
345 InsecureRandomGenerator gen;
346 // Fix the seed to make the test non-flaky.
347 gen.ReseedForTesting(kIterations + 1);
348 bool pass = ChiSquaredTest(gen, samples, start_bit, 8);
352 // We exclude 1% on each side, so we expect 98% of tests to pass, meaning 98
353 // * kIterations / 100. However this is asymptotic, so add a bit of leeway.
354 int expected_pass_count = (kIterations * 98) / 100;
355 EXPECT_GE(pass_count, expected_pass_count - ((kIterations * 2) / 100))
356 << "For start_bit = " << start_bit;
360 TEST(RandUtilTest, InsecureRandomGeneratorRandDouble) {
361 InsecureRandomGenerator gen;
363 for (int i = 0; i < 1000; i++) {
364 volatile double x = gen.RandDouble();