It is not. Sha1 is designed to be fast. You want your password hash function to be slow, so that an attacker has to spend as much resources as possible to brute

It is not. Sha1 is designed to be fast. You want your password hash function to be slow, so that an attacker has to spend as much resources as possible to brute force it. Of course, it does not mean you should take a slow implementation of a fast hash. You need a hash that, when implemented to be as fast as possible, still is pretty slow.