New Circuit for Quantum Adder by Constant

We propose a new circuit for in-place addition of a classical $n$-bit constant to a quantum $n$-qubit integer modulo $2^n$. Our circuit uses $n-3$ ancilla qubits and has a T-count of $4n-5$. We also propose controlled version of this circuit that uses $n-2$ ancillas and has a T-count of $11n-15$. We implement these circuits in Q#.