<p>What about the more simpler</p>
<div class="highlight highlight-source-c"><pre>  <span class="pl-k">unsigned</span> a, d;
  <span class="pl-k">__asm__</span> <span class="pl-en">volatile</span>(<span class="pl-s"><span class="pl-pds">"</span>rdtsc<span class="pl-pds">"</span></span> : <span class="pl-s"><span class="pl-pds">"</span>=a<span class="pl-pds">"</span></span> (a), "=d" (d));
  value= ((<span class="pl-k">unsigned</span> <span class="pl-k">long</span> <span class="pl-k">long</span>)a) | (((<span class="pl-k">unsigned</span> <span class="pl-k">long</span> <span class="pl-k">long</span>)d) << <span class="pl-c1">32</span>);</pre></div>
<p>which should work for both x86 and x86_64 according to <a href="https://web.archive.org/web/20161215213659/http://www.cs.wm.edu/%7Ekearns/001lab.d/rdtsc.html" rel="nofollow">https://web.archive.org/web/20161215213659/http://www.cs.wm.edu/~kearns/001lab.d/rdtsc.html</a> ?</p>

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