base/rand_util_unittest.cc

   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
  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
  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
  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
  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().
  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
  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
 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.
 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 }