| // 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 <gtest/gtest.h> |
| |
| #include "base/logging.h" |
| #include "base/time/time.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."; |
| } |