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POWhy c++ program compiled for x64 platform is slower than compiled for x86?
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  1. POWhy c++ program compiled for x64 platform is slower than compiled for x86?
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    copied!<p>I've wrote program, and compiled it for x64 and x86 platform in Visual Studio 2010 on Intel Core i5-2500. x64 version take about 19 seconds for execution and x86 take about 17 seconds. What can be the reason of such behavior?</p> <pre><code>#include "timer.h" #include &lt;vector&gt; #include &lt;iostream&gt; #include &lt;algorithm&gt; #include &lt;string&gt; #include &lt;sstream&gt; /********************DECLARATIONS************************************************/ class Vector { public: Vector():x(0),y(0),z(0){} Vector(double x, double y, double z) : x(x) , y(y) , z(z) { } double x; double y; double z; }; double Dot(const Vector&amp; a, const Vector&amp; b) { return a.x * b.x + a.y * b.y + a.z * b.z; } class Vector2 { public: typedef double value_type; Vector2():x(0),y(0){} Vector2(double x, double y) : x(x) , y(y) { } double x; double y; }; /******************************TESTS***************************************************/ void Test(const std::vector&lt;Vector&gt;&amp; m, std::vector&lt;Vector2&gt;&amp; m2) { Vector axisX(0.3f, 0.001f, 0.25f); Vector axisY(0.043f, 0.021f, 0.45f); std::vector&lt;Vector2&gt;::iterator i2 = m2.begin(); std::for_each(m.begin(), m.end(), [&amp;](const Vector&amp; v) { Vector2 r(0,0); r.x = Dot(axisX, v); r.y = Dot(axisY, v); (*i2) = r; ++i2; }); } int main() { cpptask::Timer timer; int len2 = 300; size_t len = 5000000; std::vector&lt;Vector&gt; m; m.reserve(len); for (size_t i = 0; i &lt; len; ++i) { m.push_back(Vector(i * 0.2345, i * 2.67, i * 0.98)); } /***********************************************************************************/ { std::vector&lt;Vector2&gt; m2(m.size()); double time = 0; for (int i = 0; i &lt; len2; ++i) { timer.Start(); Test(m, m2); time += timer.End(); } std::cout &lt;&lt; "Dot product double - " &lt;&lt; time / len2 &lt;&lt; std::endl; } /***********************************************************************************/ return 0; } </code></pre>
 

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