Games : How do weapon modifiers stack with other bonuses in Terraria?

If I have a weapon with a +X% damage modifier (e.g. Ruthless) while also having +Y% total other damage bonuses (from accessories, buffs, etc...), will the total damage be:

Multiplicative: (BaseDamage * (100% + X%)) * (100% + Y%)

OR

Additive: BaseDamage * (100% + X% + Y%)