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// Copyright 2016 The Cobalt Authors. All Rights Reserved.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
#include "starboard/nplb/random_helpers.h"
#include <limits>
#include "starboard/system.h"
#include "testing/gtest/include/gtest/gtest.h"
namespace starboard {
namespace nplb {
void TestProducesBothValuesOfAllBits(RandomFunction get_random) {
const uint64_t kAllZeros = SB_UINT64_C(0);
const uint64_t kAllOnes = ~kAllZeros;
const int kTrialCount = 1000;
uint64_t found_ones = kAllZeros;
uint64_t found_zeros = kAllOnes;
for (size_t i = 0; i < kTrialCount; ++i) {
uint64_t value = get_random();
found_ones |= value;
found_zeros &= value;
if (found_zeros == kAllZeros && found_ones == kAllOnes)
return;
}
ADD_FAILURE() << "Didn't achieve all bit values in maximum number of tries.";
}
void TestIsFairlyUniform(RandomFunction get_random) {
const uint64_t kTopOfRange = std::numeric_limits<uint64_t>::max();
const uint64_t kExpectedAverage = kTopOfRange / SB_UINT64_C(2);
const uint64_t kAllowedVariance = kExpectedAverage / SB_UINT64_C(50);
const int kMinAttempts = 1000;
const int kMaxAttempts = 1000000;
double cumulative_average = 0.0;
int count = 0;
while (count < kMaxAttempts) {
uint64_t value = get_random();
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;
}
EXPECT_LT(count, kMaxAttempts) << "Expected average was " << kExpectedAverage
<< ", average ended at " << cumulative_average;
}
} // namespace nplb
} // namespace starboard