mrb_value a = RARRAY_PTR(arys_ary)[j]; // arys[j]

mrb_check_type(mrb, a, MRB_TT_ARRAY);

mrb_int b = RARRAY_LEN(a); // a.size

if (b <= 0) {

mrb_raise(mrb, E_ARGUMENT_ERROR, "cannot compute product with an empty array");

}

mrb_ary_set(mrb, group, j + 1, RARRAY_PTR(a)[n % b]);

n /= b;

}

if (n >= RARRAY_LEN(self_ary)) {

mrb_raise(mrb, E_INDEX_ERROR, "index out of range");

}

mrb_ary_set(mrb, group, 0, RARRAY_PTR(self_ary)[n]);

return group;