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POC++11 tuple performance
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  1. POC++11 tuple performance
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    copied!<p>I just about to make my code more generalized by using <code>std::tuple</code> in a lot of cases including single element. I mean for example <code>tuple&lt;double&gt;</code> instead of <code>double</code>. But I decided to check performance of this particular case.</p> <p>Here is simple performance benchmark test:</p> <pre><code>#include &lt;tuple&gt; #include &lt;iostream&gt; using std::cout; using std::endl; using std::get; using std::tuple; int main(void) { #ifdef TUPLE using double_t = std::tuple&lt;double&gt;; #else using double_t = double; #endif constexpr int count = 1e9; auto array = new double_t[count]; long long sum = 0; for (int idx = 0; idx &lt; count; ++idx) { #ifdef TUPLE sum += get&lt;0&gt;(array[idx]); #else sum += array[idx]; #endif } delete[] array; cout &lt;&lt; sum &lt;&lt; endl; // just "external" side effect for variable sum. } </code></pre> <p>And run results:</p> <pre><code>$ g++ -DTUPLE -O2 -std=c++11 test.cpp &amp;&amp; time ./a.out 0 real 0m3.347s user 0m2.839s sys 0m0.485s $ g++ -O2 -std=c++11 test.cpp &amp;&amp; time ./a.out 0 real 0m2.963s user 0m2.424s sys 0m0.519s </code></pre> <p>I thought that tuple is strict static-compiled template and all of get&lt;> functions are working just usual variable access in that case. BTW memory allocation sizes in this test are same. Why does this execution time difference happens?</p> <p>EDIT: Problem was in initialization of tuple&lt;> object. To make test more accurate one line must be changed:</p> <pre><code> constexpr int count = 1e9; - auto array = new double_t[count]; + auto array = new double_t[count](); long long sum = 0; </code></pre> <p>After that one can observe similar results:</p> <pre><code>$ g++ -DTUPLE -g -O2 -std=c++11 test.cpp &amp;&amp; (for i in $(seq 3); do time ./a.out; done) 2&gt;&amp;1 | grep real real 0m3.342s real 0m3.339s real 0m3.343s $ g++ -g -O2 -std=c++11 test.cpp &amp;&amp; (for i in $(seq 3); do time ./a.out; done) 2&gt;&amp;1 | grep real real 0m3.349s real 0m3.339s real 0m3.334s </code></pre>
 

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