Attack speed formula

is there some type of attack speed formula out there I can plug into a calculator real quick? I need to figure out how much attack speed I need to hit with 1.5 second claws with 3 charge frenzy dual wielding and the attack speed bonus applied to frenzy itself. I'm aiming for 4 attacks per second. I noticed when I was using rapier that going from 1.7 speed rapiers to 1.5 and 1.35 was a major decrease in time between attacks. that same amount of speed added also didn't pack as much of a punch the faster my weapon got after a certain point.

I would also like to know the formula for attack speed I've been searching for a couple hours now and I can't find it though it is pretty late so I may have missed it.

Weapon base * (1 + local attack speed on weapon) * (1 + increased attack speed on passives and items) * (1 + more attack speed)

So, if your claws have 1,5 attack per second including local speed increase, and you got 12% increased attack speed from frenzy charges you would need to take...

1,5 * (1 + X + 0,12) = 4
X = 154% increased attack speed

And if you used L20 multistrike

1,5 * (1 + X + 0,12) * (1 + 0,94) = 4
X = 25% increased attack speed

What you noticed about gain from taking increased attack speed bonuses getting smaller, it's because 'increased bonuses' stack additively with each other, the more you got, the less significant each additional point becomes.