title: Way to print out compile-time -calculated constants
body: <p>I'm doing some microcontroller programming and I have code along these lines:</p>
  
  <pre><code>#define F_CPU 8000000
  #define F_ADC (F_CPU / 64.0)
  #define T_ADC (1.0/F_ADC)
  </code></pre>
  
  <p>Is there a way to print out the calculated values of, say T_ADC at compile time?  I tried stringifying it </p>
  
  <pre><code>#define STRINGIFY(s) XSTRINGIFY(s)
  #define XSTRINGIFY(s) #s
  #pragma message ("T_ADC " STRINGIFY(T_ADC)) 
  </code></pre>
  
  <p>But that just gives the macro-expansion "(1/(8000000/64))", not the actual value.</p>
  
  <p>This being a micro-controller program, it's awkward to do a <code>printf</code> at startup time.  I'm using gcc and I'm happy to use any non-standard gcc features if that helps.</p>