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// 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 <gtest/gtest.h>
#include "base/logging.h"
#include "base/memory/scoped_ptr.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.";
}
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