attackdamage.java

@Override
public Multimap getAttributeModifiers(ItemStack stack) {
	Multimap multimap = super.getAttributeModifiers(stack);
	double damage = /* ... */;
	multimap.put(SharedMonsterAttributes.attackDamage.getAttributeUnlocalizedName(),
	        new AttributeModifier(field_111210_e, "<My item> damage modifier", damage, 0));
	return multimap;
}