Base52 url shortener perfect hash function in C

No AEIOU because of fear of spelling naughty words?<p>Over what set of inputs is this claimed to be a 'perfect hash'?<p><a href="http://en.wikipedia.org/wiki/Perfect_hash" rel="nofollow">http://en.wikipedia.org/wiki/Perfect_hash</a><p>I guess I'm missing the point. Is an explanation of the motivation for this anywhere?

So what does likely() do?

If your answer is a url shortener you are asking the wrong question.