Source code for qrisp.alg_primitives.arithmetic.adders.fourier_adder

"""
********************************************************************************
* Copyright (c) 2025 the Qrisp authors
*
* This program and the accompanying materials are made available under the
* terms of the Eclipse Public License 2.0 which is available at
* http://www.eclipse.org/legal/epl-2.0.
*
* This Source Code may also be made available under the following Secondary
* Licenses when the conditions for such availability set forth in the Eclipse
* Public License, v. 2.0 are satisfied: GNU General Public License, version 2
* with the GNU Classpath Exception which is
* available at https://www.gnu.org/software/classpath/license.html.
*
* SPDX-License-Identifier: EPL-2.0 OR GPL-2.0 WITH Classpath-exception-2.0
********************************************************************************
"""

import numpy as np

from qrisp.alg_primitives import QFT
from qrisp.core.gate_application_functions import p, cz
from qrisp.environments import QuantumEnvironment, conjugate
from qrisp.circuit import Operation, PGate, QuantumCircuit




def fourier_adder(a, b, perform_QFT=True):
    """
    In-place adder function based on `this paper <https://arxiv.org/abs/quant-ph/0410184>`__
    Performs the addition

    ::

        b += a


    Parameters
    ----------
    a : int or QuantumVariable or list[Qubit]
        The value that should be added.
    b : QuantumVariable or list[Qubit]
        The value that should be modified in the in-place addition.
    perform_QFT : bool, optional
        If set to ``False``, no QFT is executed. The default is ``True``.

    Examples
    --------

    We add two integers:

    >>> from qrisp import QuantumFloat, fourier_adder
    >>> a = QuantumFloat(4)
    >>> b = QuantumFloat(4)
    >>> a[:] = 4
    >>> b[:] = 5
    >>> fourier_adder(a,b)
    >>> print(b)
    {9: 1.0}

    """

    if perform_QFT:
        env = conjugate(QFT)(b, exec_swap=False)
    else:
        env = QuantumEnvironment()

    with env:

        b = list(b)
        b = b[::-1]

        if isinstance(a, int):
            for i in range(len(b)):
                p(a * np.pi * 2 ** (1 + i - len(b)), b[i])

        else:

            if len(a) > len(b):
                raise Exception(
                    "Tried to add QuantumFloat of higher precision onto QuantumFloat of lower precision"
                )

            phase_correction_a = np.zeros(len(a))
            phase_correction_b = np.zeros(len(b))
            for j in range(len(a)):
                for i in range(len(b)):

                    if 1 + j + i - len(b) >= 1:
                        continue
                    if 1 + j + i - len(b) == 0:
                        cz(a[j], b[i])
                    else:
                        b[i].qs().append(
                            QuasiRZZ(-np.pi * 2 ** (1 + j + i - len(b)) / 2),
                            [a[j], b[i]],
                        )

                        phase_correction_a[j] += np.pi * 2 ** (1 + j + i - len(b)) / 2
                        phase_correction_b[i] += np.pi * 2 ** (1 + j + i - len(b)) / 2

            for i in range(len(b)):
                if phase_correction_b[i] % (2 * np.pi) != 0:
                    p(phase_correction_b[i], b[i])
            for i in range(len(a)):
                if phase_correction_a[i] % (2 * np.pi) != 0:
                    p(phase_correction_a[i], a[i])



class QuasiRZZ(Operation):

    def __init__(self, angle):
        qc = QuantumCircuit(2)
        qc.cx(qc.qubits[1], qc.qubits[0])
        qc.p(angle, qc.qubits[0])
        qc.cx(qc.qubits[1], qc.qubits[0])

        Operation.__init__(
            self, "quasi_rzz", num_qubits=2, definition=qc, params=[angle]
        )

        self.permeability = {0: True, 1: True}
        self.is_qfree = True

    def inverse(self):
        return QuasiRZZ(-self.params[0])

    def control(self, num_ctrl_qubits=1, ctrl_state=-1, method=None):

        qc = QuantumCircuit(2 + num_ctrl_qubits)
        qc.cx(qc.qubits[-1], qc.qubits[-2])
        qc.append(
            PGate(self.params[0]).control(
                num_ctrl_qubits, ctrl_state=ctrl_state, method=method
            ),
            qc.qubits[:-1],
        )
        qc.cx(qc.qubits[-1], qc.qubits[-2])

        res = Operation.control(
            self, num_ctrl_qubits, ctrl_state=ctrl_state, method=method
        )

        res.definition = qc
        return res