123 lines
4.0 KiB
C++
123 lines
4.0 KiB
C++
// Copyright (c) 2011 The Chromium Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style license that can be
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// found in the LICENSE file.
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#include "base/rand_util.h"
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#include <algorithm>
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#include <limits>
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#include "testing/gtest/include/gtest/gtest.h"
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namespace {
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const int kIntMin = std::numeric_limits<int>::min();
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const int kIntMax = std::numeric_limits<int>::max();
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} // namespace
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TEST(RandUtilTest, SameMinAndMax) {
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EXPECT_EQ(base::RandInt(0, 0), 0);
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EXPECT_EQ(base::RandInt(kIntMin, kIntMin), kIntMin);
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EXPECT_EQ(base::RandInt(kIntMax, kIntMax), kIntMax);
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}
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TEST(RandUtilTest, RandDouble) {
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// Force 64-bit precision, making sure we're not in a 80-bit FPU register.
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volatile double number = base::RandDouble();
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EXPECT_GT(1.0, number);
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EXPECT_LE(0.0, number);
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}
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TEST(RandUtilTest, RandBytes) {
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const size_t buffer_size = 50;
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char buffer[buffer_size];
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memset(buffer, 0, buffer_size);
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base::RandBytes(buffer, buffer_size);
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std::sort(buffer, buffer + buffer_size);
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// Probability of occurrence of less than 25 unique bytes in 50 random bytes
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// is below 10^-25.
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EXPECT_GT(std::unique(buffer, buffer + buffer_size) - buffer, 25);
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}
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TEST(RandUtilTest, RandBytesAsString) {
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std::string random_string = base::RandBytesAsString(1);
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EXPECT_EQ(1U, random_string.size());
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random_string = base::RandBytesAsString(145);
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EXPECT_EQ(145U, random_string.size());
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char accumulator = 0;
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for (size_t i = 0; i < random_string.size(); ++i)
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accumulator |= random_string[i];
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// In theory this test can fail, but it won't before the universe dies of
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// heat death.
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EXPECT_NE(0, accumulator);
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}
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// Make sure that it is still appropriate to use RandGenerator in conjunction
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// with std::random_shuffle().
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TEST(RandUtilTest, RandGeneratorForRandomShuffle) {
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EXPECT_EQ(base::RandGenerator(1), 0U);
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EXPECT_LE(std::numeric_limits<ptrdiff_t>::max(),
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std::numeric_limits<int64>::max());
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}
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TEST(RandUtilTest, RandGeneratorIsUniform) {
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// Verify that RandGenerator has a uniform distribution. This is a
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// regression test that consistently failed when RandGenerator was
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// implemented this way:
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//
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// return base::RandUint64() % max;
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//
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// A degenerate case for such an implementation is e.g. a top of
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// range that is 2/3rds of the way to MAX_UINT64, in which case the
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// bottom half of the range would be twice as likely to occur as the
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// top half. A bit of calculus care of jar@ shows that the largest
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// measurable delta is when the top of the range is 3/4ths of the
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// way, so that's what we use in the test.
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const uint64 kTopOfRange = (std::numeric_limits<uint64>::max() / 4ULL) * 3ULL;
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const uint64 kExpectedAverage = kTopOfRange / 2ULL;
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const uint64 kAllowedVariance = kExpectedAverage / 50ULL; // +/- 2%
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const int kMinAttempts = 1000;
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const int kMaxAttempts = 1000000;
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double cumulative_average = 0.0;
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int count = 0;
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while (count < kMaxAttempts) {
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uint64 value = base::RandGenerator(kTopOfRange);
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cumulative_average = (count * cumulative_average + value) / (count + 1);
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// Don't quit too quickly for things to start converging, or we may have
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// a false positive.
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if (count > kMinAttempts &&
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kExpectedAverage - kAllowedVariance < cumulative_average &&
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cumulative_average < kExpectedAverage + kAllowedVariance) {
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break;
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}
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++count;
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}
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ASSERT_LT(count, kMaxAttempts) << "Expected average was " <<
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kExpectedAverage << ", average ended at " << cumulative_average;
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}
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TEST(RandUtilTest, RandUint64ProducesBothValuesOfAllBits) {
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// This tests to see that our underlying random generator is good
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// enough, for some value of good enough.
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uint64 kAllZeros = 0ULL;
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uint64 kAllOnes = ~kAllZeros;
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uint64 found_ones = kAllZeros;
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uint64 found_zeros = kAllOnes;
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for (size_t i = 0; i < 1000; ++i) {
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uint64 value = base::RandUint64();
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found_ones |= value;
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found_zeros &= value;
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if (found_zeros == kAllZeros && found_ones == kAllOnes)
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return;
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}
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FAIL() << "Didn't achieve all bit values in maximum number of tries.";
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}
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