title: How bad rand from stdlib.h is?
body: <p>I'm making a monte carlo simulation in C++ and I was using Boost for random numbers. I used GSL a bit too. But it turns out random number generation is one of my biggest runtime inefficiencies, so I just started using good old <code>rand()</code> from <code>cstdlib</code>. </p>
  
  <p>How badly am I risking to have poor random number properties on my simulation? I use around 10^6 or 10^7 random number samples.</p>