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POState of "memset" functionality in C++ with modern compilers
 

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    <h2>Context:</h2> <p>A while ago, I stumbled upon this 2001 DDJ article by Alexandrescu: <a href="http://www.ddj.com/cpp/184403799" rel="noreferrer">http://www.ddj.com/cpp/184403799</a></p> <p>It's about comparing various ways to initialized a buffer to some value. Like what "memset" does for single-byte values. He compared various implementations (memcpy, explicit "for" loop, duff's device) and did not really find the best candidate across all dataset sizes and all compilers.</p> <p>Quote:</p> <blockquote> <p>There is a very deep, and sad, realization underlying all this. We are in 2001, the year of the Spatial Odyssey. (...) Just step out of the box and look at us — after 50 years, we're still not terribly good at filling and copying memory.</p> </blockquote> <h2>Question:</h2> <ol> <li>does anyone have more recent information about this problem ? Do recent GCC and Visual C++ implementations perform significantly better than 7 years ago ? <li>I'm writing code that has a lifetime of 5+ (probably 10+) years and that will process arrays' sizes from a few bytes to hundred of megabytes. I can't assume that my choices now will still be optimal in 5 years. What should I do: <ul> <li>a) use the system's memset (or equivalent) and forget about optimal performance or assume the runtime and compiler will handle this for me. <li>b) benchmark once and for all on various array sizes and compilers and switch at runtime between several routines. <li>c) run the benchmark at program initialization and switch at runtime based on accurate (?) data. </ul> </ol> <p>Edit: I'm working on image processing software. My array items are PODs and every millisecond counts !</p> <p>Edit 2: Thanks for the first answers, here are some additional informations:<ul><li>Buffer initialization may represent 20%-40% of total runtime of some algorithms. <li>The platform may vary in the next 5+ years, although it will stay in the "fastest CPU money can buy from DELL" category. Compilers will be some form of GCC and Visual C++. No embedded stuff or exotic architectures on the radar<li>I'd like to hear from people who had to update their software when MMX and SSE appeared, since I'll have to do the same when "SSE2015" becomes available... :) </ul></p>
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