1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
|
// Copyright (c) 2011 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#include "base/rand_util.h"
#include <stddef.h>
#include <stdint.h>
#include <algorithm>
#include <limits>
#include <memory>
#include "base/logging.h"
#include "base/time/time.h"
#include "testing/gtest/include/gtest/gtest.h"
namespace {
const int kIntMin = std::numeric_limits<int>::min();
const int kIntMax = std::numeric_limits<int>::max();
} // namespace
TEST(RandUtilTest, RandInt) {
EXPECT_EQ(base::RandInt(0, 0), 0);
EXPECT_EQ(base::RandInt(kIntMin, kIntMin), kIntMin);
EXPECT_EQ(base::RandInt(kIntMax, kIntMax), kIntMax);
// Check that the DCHECKS in RandInt() don't fire due to internal overflow.
// There was a 50% chance of that happening, so calling it 40 times means
// the chances of this passing by accident are tiny (9e-13).
for (int i = 0; i < 40; ++i)
base::RandInt(kIntMin, kIntMax);
}
TEST(RandUtilTest, RandDouble) {
// Force 64-bit precision, making sure we're not in a 80-bit FPU register.
volatile double number = base::RandDouble();
EXPECT_GT(1.0, number);
EXPECT_LE(0.0, number);
}
TEST(RandUtilTest, RandBytes) {
const size_t buffer_size = 50;
char buffer[buffer_size];
memset(buffer, 0, buffer_size);
base::RandBytes(buffer, buffer_size);
std::sort(buffer, buffer + buffer_size);
// Probability of occurrence of less than 25 unique bytes in 50 random bytes
// is below 10^-25.
EXPECT_GT(std::unique(buffer, buffer + buffer_size) - buffer, 25);
}
TEST(RandUtilTest, RandBytesAsString) {
std::string random_string = base::RandBytesAsString(1);
EXPECT_EQ(1U, random_string.size());
random_string = base::RandBytesAsString(145);
EXPECT_EQ(145U, random_string.size());
char accumulator = 0;
for (size_t i = 0; i < random_string.size(); ++i)
accumulator |= random_string[i];
// In theory this test can fail, but it won't before the universe dies of
// heat death.
EXPECT_NE(0, accumulator);
}
// Make sure that it is still appropriate to use RandGenerator in conjunction
// with std::random_shuffle().
TEST(RandUtilTest, RandGeneratorForRandomShuffle) {
EXPECT_EQ(base::RandGenerator(1), 0U);
EXPECT_LE(std::numeric_limits<ptrdiff_t>::max(),
std::numeric_limits<int64_t>::max());
}
TEST(RandUtilTest, RandGeneratorIsUniform) {
// Verify that RandGenerator has a uniform distribution. This is a
// regression test that consistently failed when RandGenerator was
// implemented this way:
//
// return base::RandUint64() % max;
//
// A degenerate case for such an implementation is e.g. a top of
// range that is 2/3rds of the way to MAX_UINT64, in which case the
// bottom half of the range would be twice as likely to occur as the
// top half. A bit of calculus care of jar@ shows that the largest
// measurable delta is when the top of the range is 3/4ths of the
// way, so that's what we use in the test.
const uint64_t kTopOfRange =
(std::numeric_limits<uint64_t>::max() / 4ULL) * 3ULL;
const uint64_t kExpectedAverage = kTopOfRange / 2ULL;
const uint64_t kAllowedVariance = kExpectedAverage / 50ULL; // +/- 2%
const int kMinAttempts = 1000;
const int kMaxAttempts = 1000000;
double cumulative_average = 0.0;
int count = 0;
while (count < kMaxAttempts) {
uint64_t value = base::RandGenerator(kTopOfRange);
cumulative_average = (count * cumulative_average + value) / (count + 1);
// Don't quit too quickly for things to start converging, or we may have
// a false positive.
if (count > kMinAttempts &&
kExpectedAverage - kAllowedVariance < cumulative_average &&
cumulative_average < kExpectedAverage + kAllowedVariance) {
break;
}
++count;
}
ASSERT_LT(count, kMaxAttempts) << "Expected average was " <<
kExpectedAverage << ", average ended at " << cumulative_average;
}
TEST(RandUtilTest, RandUint64ProducesBothValuesOfAllBits) {
// This tests to see that our underlying random generator is good
// enough, for some value of good enough.
uint64_t kAllZeros = 0ULL;
uint64_t kAllOnes = ~kAllZeros;
uint64_t found_ones = kAllZeros;
uint64_t found_zeros = kAllOnes;
for (size_t i = 0; i < 1000; ++i) {
uint64_t value = base::RandUint64();
found_ones |= value;
found_zeros &= value;
if (found_zeros == kAllZeros && found_ones == kAllOnes)
return;
}
FAIL() << "Didn't achieve all bit values in maximum number of tries.";
}
// Benchmark test for RandBytes(). Disabled since it's intentionally slow and
// does not test anything that isn't already tested by the existing RandBytes()
// tests.
TEST(RandUtilTest, DISABLED_RandBytesPerf) {
// Benchmark the performance of |kTestIterations| of RandBytes() using a
// buffer size of |kTestBufferSize|.
const int kTestIterations = 10;
const size_t kTestBufferSize = 1 * 1024 * 1024;
std::unique_ptr<uint8_t[]> buffer(new uint8_t[kTestBufferSize]);
const base::TimeTicks now = base::TimeTicks::Now();
for (int i = 0; i < kTestIterations; ++i)
base::RandBytes(buffer.get(), kTestBufferSize);
const base::TimeTicks end = base::TimeTicks::Now();
LOG(INFO) << "RandBytes(" << kTestBufferSize << ") took: "
<< (end - now).InMicroseconds() << "µs";
}
|
