"Officially" (or so I believe) English doesn't have comparative adverbs (a single word rather than "more" + an adverb), but *faster* is in common usage as one, for example:

> 
> Do it faster
> 
> 
> 

When strictly speaking one should say:

> 
> Do it more quickly
> 
> 
> 

Is the former an error in grammar? Or has English (d)evolved to such an extent that *faster* may be used as a comparative adverb?