That would surely eat the gain, or even more, what we earn with "hardcoded-keys-inline-crypting"... 

Currently, i'm not aware of a collision in md5 and sha1 simultaneously. Maybe one user get, maybe in 100 or 1000 years, a collision there with md5. Fallback is then sha1 (respectively vise versa).

How extremly minimal is the chance to trigger a collision for both with the same text? 
Maybe the sun will disappeare first :-) or?

I offer:
```$code_hash = md5(...) . sha1(...) . function_exists('hash') ? hash('whirlpool', '...') : ''```
:-) 
sha1 as 1st fallback, and, if exists (since php5.1.2) whirlpool as 2nd.

That would not eat our inline-crypt gain and is, practicaly, out of any collision range.

And if we even ever hear about any collision then there... that information would it absolut worth: A simultan-collision in three one-way-hashes. 

Want we make it so? At least until we found a more perfect (and not gain-eating) solution.