A speed increase of 30% means 70% hit delay. Weapon speed is set as a delay, thus a slower weapon speed as "attack speed" increases. Ironic, huh?
So attack speed (or delay) times 0.7 (70 percent).
Example:
2500 originally with 30% haste is 2500 x 0.7 which is now 1750
2500 originally with 50% haste is 2500 x 0.5 wich is now 1250
This is typically how I calculate things. It's either sir's method or Plus'. this is not fun and games we have to know there things when we put the bigboy pants on at work. So we gotta figure this out.
Ok I timed punching over 3 minutes to see and it does subtract. Punching with my ranger is 2500 speed and with gloves I timed 1745 calculated if you simply subtract is 1750. A 30% increase would have been 1923. My testing before was too fast and not as accurate.
So maybe I'll test more but subtraction is correct for the 30% gloves hopefully it scales to the rest.
New speed = old speed ( 1 - %haste). Where haste is a actual % like 30% = .3, 10% = .1 etc.