title: C++ next float with numeric_limits / epsilon?
body: <p>Consider a "normal" real number <code>TREAL x</code> in C++ (not subnormal and not NaN/Infinite) (<code>TREAL</code> = <code>float</code>, <code>double</code>, <code>long double</code>)<br>
  Is the following the good solution to find the previous and next <code>x</code> from a floating-point point of view ?</p>
  
  <pre><code>TREAL xprev = (((TREAL)(1.)) - std::numeric_limits&lt;TREAL&gt;::epsilon()) * x;
  TREAL xnext = (((TREAL)(1.)) + std::numeric_limits&lt;TREAL&gt;::epsilon()) * x;
  </code></pre>
  
  <p>Thank you very much.</p>