[huhtenberg]

That code is really bad. Dunno about you, but to me this handcrafted entanglement looks like the crap that any professional programmer should be ashamed of:

  if ( .. )
  {
     for ( .. )
     {
  label:
        ...
     }
  }
  else
  {
     if ( .. )
     {
       ..
     }
     else
       goto label;
     ..
   }

The actual code is even worse than this as there's a second goto that jumps from the top for into one of else blocks at the bottom from where the control can go back to for via another goto ... I sort of can see how this code came about, but there is absolutely no excuse for checking in something this f*cked up.

If they wanted to show off, they should've just used the coroutines :-)

[coliveira]

It has been explained that this is just a way of implementing a fast lexical scanner. This is the kind of code that you don't come up with, it is a mechanical implementation of a state machine.

[huhtenberg]

Mechanical or not, this is a very untidy way of implementing a "fast lexical scanner". Even the Duff's device looks cleaner and more elegant in comparison. And it's not like there is a shortage of other implementation options that are as fast.