84 lines
3.6 KiB
C++
84 lines
3.6 KiB
C++
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// fig17_02.cpp
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// Performing transforms with execution policies par and unseq.
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#include <algorithm>
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#include <chrono> // for timing operations
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#include <cmath>
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#include <execution> // for execution policies
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#include <fmt/format.h>
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#include <iostream>
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#include <random>
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#include <vector>
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// time each std::transform call and return its duration in seconds
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double timeTransform(auto policy, const std::vector<int>& v) {
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// <chrono> library features we'll use for timing
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using std::chrono::steady_clock;
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using std::chrono::duration_cast;
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using std::chrono::milliseconds;
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std::vector<double> result(v.size());
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auto start{steady_clock::now()}; // get current time
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std::transform(policy, v.begin(), v.end(),
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result.begin(), [](auto x) {return std::sqrt(x);});
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auto end{steady_clock::now()}; // get current time
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// calculate and return time in seconds
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auto time{duration_cast<milliseconds>(end - start)};
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return time.count() / 1000.0;
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}
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int main() {
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// set up random-number generation
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std::random_device rd;
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std::default_random_engine engine{rd()};
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std::uniform_int_distribution ints{0, 1000};
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std::cout << "Creating vectors\n";
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std::vector<int> v1(100'000'000);
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std::vector<int> v2(1'000'000'000);
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std::cout << "Filling vectors with random ints\n";
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std::generate(std::execution::par, v1.begin(), v1.end(),
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[&]() {return ints(engine);});
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std::generate(std::execution::par, v2.begin(), v2.end(),
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[&]() {return ints(engine);});
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std::cout << "\nCalculating square roots:\n";
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// time the transforms on 100,000,000 elements
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std::cout << fmt::format("{} elements with par\n", v1.size());
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double parTime1{timeTransform(std::execution::par, v1)};
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std::cout << fmt::format("{} elements with unseq\n", v1.size());
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double unseqTime1{timeTransform(std::execution::unseq, v1)};
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// time the transforms on 1,000,000,000 elements
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std::cout << fmt::format("{} elements with par\n", v2.size());
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double parTime2{timeTransform(std::execution::par, v2)};
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std::cout << fmt::format("{} elements with unseq\n", v2.size());
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double unseqTime2{timeTransform(std::execution::unseq, v2)};
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// display table of timing results
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std::cout << "\nExecution times (in seconds):\n\n"
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<< fmt::format("{:>13}{:>17}{:>21}\n", "# of elements",
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"par (parallel)", "unseq (vectorized)")
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<< fmt::format("{:>13}{:>17.3f}{:>21.3f}\n",
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v1.size(), parTime1, unseqTime1)
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<< fmt::format("{:>13}{:>17.3f}{:>21.3f}\n",
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v2.size(), parTime2, unseqTime2);
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}
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/**************************************************************************
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* (C) Copyright 1992-2021 by Deitel & Associates, Inc. and *
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* Pearson Education, Inc. All Rights Reserved. *
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* *
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* DISCLAIMER: The authors and publisher of this book have used their *
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* best efforts in preparing the book. These efforts include the *
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* development, research, and testing of the theories and programs *
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* to determine their effectiveness. The authors and publisher make *
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* no warranty of any kind, expressed or implied, with regard to these *
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* programs or to the documentation contained in these books. The authors *
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* and publisher shall not be liable in any event for incidental or *
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* consequential damages in connection with, or arising out of, the *
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* furnishing, performance, or use of these programs. *
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**************************************************************************/
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