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/*=========================================================================
*
* Copyright NumFOCUS
*
* 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
*
* https://www.apache.org/licenses/LICENSE-2.0.txt
*
* 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.
*
*=========================================================================*/
// First include the header file to be tested:
#include "itkMersenneTwisterRandomVariateGenerator.h"
#include <gtest/gtest.h>
#include <random> // For mt19937.
// The class to be tested.
using itk::Statistics::MersenneTwisterRandomVariateGenerator;
// Tests that GetIntegerVariate() conforms with the C++11 requirement for std::mt19937,
// when the ITK generator uses the default seed of std::mt19937:
// "The 10000th consecutive invocation of a default-constructed object of type mt19937
// shall produce the value 4123659995."
// (C++11 section "Engines and engine adaptors with predefined parameters", [rand.predef])
TEST(MersenneTwisterRandomVariateGenerator, GetIntegerVariateConformsWithStdMt19937Requirement)
{
const auto generator = MersenneTwisterRandomVariateGenerator::New();
generator->SetSeed(std::mt19937::default_seed);
for (int i = 1; i < 10000; ++i)
{
generator->GetIntegerVariate();
}
// Call GetIntegerVariate() for the 10000th time:
const auto actualValue = generator->GetIntegerVariate();
// The value required for std::mt19937 (C++11):
const auto requiredValue = 4123659995UL;
ASSERT_EQ(actualValue, requiredValue);
}
// Tests that repeated calls to GetIntegerVariate() yield the same values
// as std::mt19937, when std::mt19937 uses the same seed as the ITK generator.
TEST(MersenneTwisterRandomVariateGenerator, GetIntegerVariateReturnsSameAsStdMt19937)
{
const auto generator = MersenneTwisterRandomVariateGenerator::New();
std::mt19937 stdMt19937{ generator->GetSeed() };
// Just repeat a few times, assuming that that should be enough.
for (int i = 0; i < 10; ++i)
{
EXPECT_EQ(generator->GetIntegerVariate(), stdMt19937());
}
}
// Tests that two GetNextSeed() calls return the very same seed value, when ResetNextSeed() is called before each of
// those calls.
TEST(MersenneTwisterRandomVariateGenerator, ResetNextSeed)
{
// Call GetInstance() beforehand, to make sure the global instance is there already when calling GetNextSeed().
[[maybe_unused]] const auto globalGenerator = MersenneTwisterRandomVariateGenerator::GetInstance();
MersenneTwisterRandomVariateGenerator::ResetNextSeed();
const auto seed = MersenneTwisterRandomVariateGenerator::GetNextSeed();
MersenneTwisterRandomVariateGenerator::ResetNextSeed();
EXPECT_EQ(MersenneTwisterRandomVariateGenerator::GetNextSeed(), seed);
}
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