I'm storing several versions of a file based on a digest of the original filename and its version, like this:

$filename = sha1($original . ':' . $version);

Would it be worth it to cache the digest ($filename) in memcache as a key/value pair (the key being the original + version and value the sha1 hash), or is generating the digest quick enough (for a high traffic php web app)?

Thanks,

Johnathan