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 <algorithm>
8 #include <limits>
9
10 #include "base/logging.h"
11 #include "base/memory/scoped_ptr.h"
12 #include "base/time/time.h"
13 #include "testing/gtest/include/gtest/gtest.h"
14
15 namespace {
16
17 const int kIntMin = std::numeric_limits<int>::min();
18 const int kIntMax = std::numeric_limits<int>::max();
19
20 } // namespace
21
TEST(RandUtilTest,SameMinAndMax)22 TEST(RandUtilTest, SameMinAndMax) {
23 EXPECT_EQ(base::RandInt(0, 0), 0);
24 EXPECT_EQ(base::RandInt(kIntMin, kIntMin), kIntMin);
25 EXPECT_EQ(base::RandInt(kIntMax, kIntMax), kIntMax);
26 }
27
TEST(RandUtilTest,RandDouble)28 TEST(RandUtilTest, RandDouble) {
29 // Force 64-bit precision, making sure we're not in a 80-bit FPU register.
30 volatile double number = base::RandDouble();
31 EXPECT_GT(1.0, number);
32 EXPECT_LE(0.0, number);
33 }
34
TEST(RandUtilTest,RandBytes)35 TEST(RandUtilTest, RandBytes) {
36 const size_t buffer_size = 50;
37 char buffer[buffer_size];
38 memset(buffer, 0, buffer_size);
39 base::RandBytes(buffer, buffer_size);
40 std::sort(buffer, buffer + buffer_size);
41 // Probability of occurrence of less than 25 unique bytes in 50 random bytes
42 // is below 10^-25.
43 EXPECT_GT(std::unique(buffer, buffer + buffer_size) - buffer, 25);
44 }
45
TEST(RandUtilTest,RandBytesAsString)46 TEST(RandUtilTest, RandBytesAsString) {
47 std::string random_string = base::RandBytesAsString(1);
48 EXPECT_EQ(1U, random_string.size());
49 random_string = base::RandBytesAsString(145);
50 EXPECT_EQ(145U, random_string.size());
51 char accumulator = 0;
52 for (size_t i = 0; i < random_string.size(); ++i)
53 accumulator |= random_string[i];
54 // In theory this test can fail, but it won't before the universe dies of
55 // heat death.
56 EXPECT_NE(0, accumulator);
57 }
58
59 // Make sure that it is still appropriate to use RandGenerator in conjunction
60 // with std::random_shuffle().
TEST(RandUtilTest,RandGeneratorForRandomShuffle)61 TEST(RandUtilTest, RandGeneratorForRandomShuffle) {
62 EXPECT_EQ(base::RandGenerator(1), 0U);
63 EXPECT_LE(std::numeric_limits<ptrdiff_t>::max(),
64 std::numeric_limits<int64>::max());
65 }
66
TEST(RandUtilTest,RandGeneratorIsUniform)67 TEST(RandUtilTest, RandGeneratorIsUniform) {
68 // Verify that RandGenerator has a uniform distribution. This is a
69 // regression test that consistently failed when RandGenerator was
70 // implemented this way:
71 //
72 // return base::RandUint64() % max;
73 //
74 // A degenerate case for such an implementation is e.g. a top of
75 // range that is 2/3rds of the way to MAX_UINT64, in which case the
76 // bottom half of the range would be twice as likely to occur as the
77 // top half. A bit of calculus care of jar@ shows that the largest
78 // measurable delta is when the top of the range is 3/4ths of the
79 // way, so that's what we use in the test.
80 const uint64 kTopOfRange = (std::numeric_limits<uint64>::max() / 4ULL) * 3ULL;
81 const uint64 kExpectedAverage = kTopOfRange / 2ULL;
82 const uint64 kAllowedVariance = kExpectedAverage / 50ULL; // +/- 2%
83 const int kMinAttempts = 1000;
84 const int kMaxAttempts = 1000000;
85
86 double cumulative_average = 0.0;
87 int count = 0;
88 while (count < kMaxAttempts) {
89 uint64 value = base::RandGenerator(kTopOfRange);
90 cumulative_average = (count * cumulative_average + value) / (count + 1);
91
92 // Don't quit too quickly for things to start converging, or we may have
93 // a false positive.
94 if (count > kMinAttempts &&
95 kExpectedAverage - kAllowedVariance < cumulative_average &&
96 cumulative_average < kExpectedAverage + kAllowedVariance) {
97 break;
98 }
99
100 ++count;
101 }
102
103 ASSERT_LT(count, kMaxAttempts) << "Expected average was " <<
104 kExpectedAverage << ", average ended at " << cumulative_average;
105 }
106
TEST(RandUtilTest,RandUint64ProducesBothValuesOfAllBits)107 TEST(RandUtilTest, RandUint64ProducesBothValuesOfAllBits) {
108 // This tests to see that our underlying random generator is good
109 // enough, for some value of good enough.
110 uint64 kAllZeros = 0ULL;
111 uint64 kAllOnes = ~kAllZeros;
112 uint64 found_ones = kAllZeros;
113 uint64 found_zeros = kAllOnes;
114
115 for (size_t i = 0; i < 1000; ++i) {
116 uint64 value = base::RandUint64();
117 found_ones |= value;
118 found_zeros &= value;
119
120 if (found_zeros == kAllZeros && found_ones == kAllOnes)
121 return;
122 }
123
124 FAIL() << "Didn't achieve all bit values in maximum number of tries.";
125 }
126
127 // Benchmark test for RandBytes(). Disabled since it's intentionally slow and
128 // does not test anything that isn't already tested by the existing RandBytes()
129 // tests.
TEST(RandUtilTest,DISABLED_RandBytesPerf)130 TEST(RandUtilTest, DISABLED_RandBytesPerf) {
131 // Benchmark the performance of |kTestIterations| of RandBytes() using a
132 // buffer size of |kTestBufferSize|.
133 const int kTestIterations = 10;
134 const size_t kTestBufferSize = 1 * 1024 * 1024;
135
136 scoped_ptr<uint8[]> buffer(new uint8[kTestBufferSize]);
137 const base::TimeTicks now = base::TimeTicks::HighResNow();
138 for (int i = 0; i < kTestIterations; ++i)
139 base::RandBytes(buffer.get(), kTestBufferSize);
140 const base::TimeTicks end = base::TimeTicks::HighResNow();
141
142 LOG(INFO) << "RandBytes(" << kTestBufferSize << ") took: "
143 << (end - now).InMicroseconds() << "µs";
144 }
145