http://www.pcg-random.org/enContents © 2026 <a href="mailto:oneill@pcg-random.org">M.E. O'Neill</a> Sat, 10 Jan 2026 00:53:27 GMTNikola (getnikola.com)http://blogs.law.harvard.edu/tech/rsshttp://www.pcg-random.org/posts/simple-portable-cpp-seed-entropy.htmlM.E. O'Neill<div><p>In two recent posts, I've looked at seeding random number generators in in C++11 (looking at <a href="http://www.pcg-random.org/posts/cpp-seeding-surprises.html">what's wrong with <code>std::seed_seq</code></a> and <a href="http://www.pcg-random.org/posts/developing-a-seed_seq-alternative.html">developing something that avoids those flaws</a>), but <code>seed_seq</code> exists as a mechanism to “mix up” entropy that you give it. You still need to get that entropy from <em>somewhere</em>. So where?</p> <h3 id="sadly-stdrandom_device-is-not-your-friend">Sadly <code>std::random_device</code> Is Not Your Friend</h3> <p>The obvious source for external randomness we can use in seeding is <code>std::random_device</code>. But as I mentioned in <a href="http://www.pcg-random.org/posts/cpps-random_device.html">this post</a>,</p> <ul> <li>It's hard to make <code>std::random_device</code> conform to the requirements of a seed sequence.</li> <li>It's unspecified just how costly this “device” is to read from.</li> <li>It may not be nondeterministic at all, rendering it unfit for our purposes.</li> </ul> <p>Portable code needs to look to other sources of entropy for RNG seeding. And even if <code>std::random_device</code> works well, mixing in entropy from other sources can have a variety of benefits, including performance.</p> <p><a href="http://www.pcg-random.org/posts/simple-portable-cpp-seed-entropy.html">Read more…</a> (14 min remaining to read)</p></div>c++C++17-ideasentropyrandutilsseed_seqseedinghttp://www.pcg-random.org/posts/simple-portable-cpp-seed-entropy.htmlMon, 04 May 2015 04:37:48 GMThttp://www.pcg-random.org/posts/cpps-random_device.htmlM.E. O'Neill<div><p>Continuing my series of blog posts about seeding random number generators in C++, it's time to take a look at <code>std::random_device</code>. In this post, we'll see the many ways in which it isn't really your friend.</p> <p><a href="http://www.pcg-random.org/posts/cpps-random_device.html">Read more…</a> (5 min remaining to read)</p></div>c++C++17-ideasentropyseedinghttp://www.pcg-random.org/posts/cpps-random_device.htmlMon, 04 May 2015 03:07:48 GMT