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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.
*
*=========================================================================*/
#include <iostream>
#include "itkFixedArray.h"
#include <ctime>
#include <cstring>
int
itkFixedArrayTest2(int, char *[])
{
// Define the number of elements in the array
const unsigned int nelements = 10000000L;
// Define the number of runs used for timing
constexpr unsigned int nrun = 10;
// Declare a simple timer
clock_t t;
using ArrayType = itk::FixedArray<double, 2>;
// Declare an array of nelements FixedArray
// and add a small margin to play with pointers
// but not map outside the allocated memory
auto * vec = new ArrayType[nelements + 8];
// Fill it up with zeros
memset(vec, 0, (nelements + 8) * sizeof(ArrayType));
// Display the alignment of the array
std::cout << "Initial alignment: " << (((size_t)vec) & 7) << '\n';
// Start a simple experiment
t = clock();
double acc1 = 0.0;
for (unsigned int i = 0; i < nrun; ++i)
{
for (unsigned int j = 0; j < nelements; ++j)
{
acc1 += vec[j][0];
}
}
// Get the final timing and display it
t = clock() - t;
const double time1 = (t * 1000.0) / CLOCKS_PER_SEC;
std::cout << "Initial execution time: " << time1 << "ms\n";
// We now force an 8 bytes aligned array
// Cast the pointer to char to play with bytes
auto * p = reinterpret_cast<char *>(vec);
// Move the char pointer until it is aligned on 8 bytes
while (((size_t)p) % 8)
{
++p;
}
// Cast the 8 bytes aligned pointer back to the original type
auto * vec2 = reinterpret_cast<ArrayType *>(p);
// Make sure the new pointer is well aligned by
// displaying the alignment
std::cout << "New alignment: " << (((size_t)vec2) & 7) << '\n';
// Start the simple experiment on the 8 byte aligned array
t = clock();
double acc2 = 0.0;
for (unsigned int i = 0; i < nrun; ++i)
{
for (unsigned int j = 0; j < nelements; ++j)
{
acc2 += vec2[j][0];
}
}
// Get the final timing and display it
t = clock() - t;
const double time2 = (t * 1000.0) / CLOCKS_PER_SEC;
std::cout << "Execution time: " << time2 << "ms\n";
// Free up the memory
delete[] vec;
const double ratio = 100.0 * (time1 - time2) / time2;
const bool sameptr = (vec == vec2);
if (sameptr)
{
std::cout << "Same pointers: true" << std::endl;
}
else
{
std::cout << "Same pointers: false" << std::endl;
}
std::cout << "Performance ratio = " << ratio << '%' << std::endl;
if (!sameptr && ratio > 20.0) // tolerates only 20%
{
std::cerr << "Performance degraded below tolerance" << std::endl;
return EXIT_FAILURE;
}
// Make sure we do something with the sums otherwise everything
// could be optimized away by the compiler
if (acc1 == 0.0 && acc2 == 0.0)
{
return EXIT_SUCCESS;
}
return EXIT_FAILURE;
}
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