D'ish similar_text?

[Dgame]

On Thursday, 10 May 2018 at 20:38:12 UTC, Vladimir Panteleev 
wrote:
> On Thursday, 10 May 2018 at 20:32:11 UTC, Dgame wrote:
>>     immutable size_t len = s1.length + s2.length;
>>     percent = (len - distance) * 100.0 / len;
>
> Note that this formula will give you only 50% similarity for 
> "abc" and "def", i.e. two completely different strings. I 
> suggest to divide by max(s1.length, s2.length) instead.

Hm, that does not work either. ABC and AZB have a different 
outcome with both. How can I calculate the percentage with 
levenshtein? It's rather simple with similar_text since it 
returns the amount of similar chars.