Function cost_entry_index 

pub fn cost_entry_index<S>(
    spell: &SpellDataFlat,
    resource_type: Option<i32>,
    active_aura_spell_ids: &HashSet<i32, S>,
) -> u8
where
    S: BuildHasher,

1-based DBC power-cost entry index for the resource type’s cost; 0 when absent.