Function arith 

pub fn arith(
    state: &mut LuaState,
    op: ArithOp,
    p1: &LuaValue,
    p2: &LuaValue,
    res: StackIdx,
) -> Result<(), LuaError>

Performs arithmetic for opcode op, writing the result to the stack slot res. Falls back to a binary tag-method if raw arithmetic is not possible.

C: void luaO_arith (lua_State *L, int op, const TValue *p1, const TValue *p2, StkId res)