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
TEST(RandUtilTest,RandInt)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
TEST(RandUtilTest,RandDouble)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
TEST(RandUtilTest,RandBytes)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
TEST(RandUtilTest,RandBytesAsString)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().
TEST(RandUtilTest,RandGeneratorForRandomShuffle)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
TEST(RandUtilTest,RandGeneratorIsUniform)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
TEST(RandUtilTest,RandUint64ProducesBothValuesOfAllBits)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.
TEST(RandUtilTest,DISABLED_RandBytesPerf)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() << "µs";
154 }
155