if you do half the weapon's hp it gets the broken condition, but what if it has the broken condition some other way (like the oracle's wrecker curse).
In other words, if an oracle(with the wrecker curse) is wielding a weapon and you sunder it, do you have to sunder all of it's HP away or start at half because it's broken?
The wrecker curse does nto lower the hp, it just gives the broken condition. It would still have full HP.
So you would need to sunder all of it's hp.