# The original version of the following code is sourced from Qiskit circuit library, and
# the original repository link is:
# https://github.com/Qiskit/qiskit/tree/f14e0b29a484795034447ea5bfb637fe845c194f
#
#
# This code is part of Qiskit.
#
# (C) Copyright IBM 2017, 2020.
#
# This code is licensed under the Apache License, Version 2.0. You may
# obtain a copy of this license in the LICENSE.txt file in the root directory
# of this source tree or at http://www.apache.org/licenses/LICENSE-2.0.
#
# Any modifications or derivative works of this code must retain this
# copyright notice, and modified files need to carry a notice indicating
# that they have been altered from the originals.
#
#
# However, this version appears deprecated in Qiskit 2.3 and later, replaced by a more efficient
# implementation. Thus, we can only trace to an available repository ((MIT License, Copyright 2025
# Yuechen Li)) that used this version for quantum software testing, where this file lies in:
# https://github.com/NahidaNahida/mstcs/blob/main/mycode/testing/IntegerComparator/programs/comp.py
#
#
# This program is adapted for use as a benchmark in controlled software testing experiments.
# Modifications made to the original code include (for Apache License 2.0):
# - Refactored to unify the inherent class as QuantumCircuit:
# - remove _invalidate() and _is_built() parts, as BlueprintCircuit is not used here
# - set self._build() in __init__ directly
from __future__ import annotations
import warnings
import numpy as np
from qiskit.circuit import QuantumCircuit, QuantumRegister, AncillaRegister
from qiskit.circuit.exceptions import CircuitError
from qiskit.circuit.library import OR
# ---------- benchmark registration ----------
from ..benchmark_registry import register_benchmark
from pathlib import Path
@register_benchmark(
Path(__file__).stem,
family=Path(__file__).resolve().parent.name,
description=(
f"Implement an integer comparison of an old version, "
f"where this version stores the comparison result in n target qubits."
),
class_name="IntegerComparatorOld",
source={
"repo": "https://github.com/NahidaNahida/mstcs",
"file": "mycode/testing/IntegerComparator/programs/comp.py",
"language": "Qiskit",
"available_doc": True
},
testability_refactoring=[
"Structure reorganization"
]
)
def create_integer_comparator_old(
num_state_qubits: int,
integer: int,
geq: bool = True,
name: str = "cmp"
):
return IntegerComparatorOld(
num_state_qubits=num_state_qubits,
value=integer,
geq=geq,
name=name
)
[docs]
class IntegerComparatorOld(QuantumCircuit):
r"""Operator compares basis states :math:`|i\rangle_n` against a classically given integer
:math:`L` of fixed value and flips a target qubit if :math:`i \geq L`
(or :math:`<` depending on the parameter ``geq``):
.. math::
|i\rangle_n |0\rangle \mapsto |i\rangle_n |i \geq L\rangle
This operation is based on two's complement implementation of binary subtraction but only
uses carry bits and no actual result bits. If the most significant carry bit
(the results bit) is 1, the :math:`\geq` condition is ``True`` otherwise it is ``False``.
"""
def __init__(
self,
num_state_qubits: int | None = None,
value: int | None = None,
geq: bool = True,
name: str = "cmp",
) -> None:
"""Create a new fixed value comparator circuit.
Args:
num_state_qubits: Number of state qubits :math:`n`.
If this is set it will determine the number of qubits required for the circuit.
value: The fixed value :math:`L` to compare with.
geq: If True, evaluate a ``>=`` condition, else ``<``.
name: Name of the circuit.
"""
super().__init__(name=name)
self._value = None
self._geq = None
self._num_state_qubits = None
self.value = value # type: ignore
self.geq = geq
self.num_state_qubits = num_state_qubits
# Build the circuit
self._build()
@property
def value(self) -> int:
"""The value to compare the qubit register to.
Returns:
The value against which the value of the qubit register is compared.
"""
return self._value # type: ignore
@value.setter
def value(self, value: int) -> None:
if value != self._value:
# self._invalidate()
self._value = value
@property
def geq(self) -> bool:
"""Return whether the comparator compares greater or less equal.
Returns:
True, if the comparator compares ``>=``, False if ``<``.
"""
return self._geq # type: ignore
@geq.setter
def geq(self, geq: bool) -> None:
"""Set whether the comparator compares greater or less equal.
Args:
geq: If True, the comparator compares ``>=``, if False ``<``.
"""
if geq != self._geq:
# self._invalidate()
self._geq = geq
@property
def num_ancilla_qubits(self):
"""Deprecated. Use num_ancillas instead."""
warnings.warn(
"The IntegerComparator.num_ancilla_qubits property is deprecated "
"as of 0.16.0. It will be removed no earlier than 3 months after the release "
"date. You should use the num_ancillas property instead."
)
return self.num_ancillas
@property
def num_state_qubits(self) -> int:
"""The number of qubits encoding the state for the comparison.
Returns:
The number of state qubits.
"""
return self._num_state_qubits # type: ignore
@num_state_qubits.setter
def num_state_qubits(self, num_state_qubits: int | None) -> None:
"""Set the number of state qubits.
Note that this will change the quantum registers.
Args:
num_state_qubits: The new number of state qubits.
"""
if self._num_state_qubits is None or num_state_qubits != self._num_state_qubits:
# self._invalidate() # reset data
self._num_state_qubits = num_state_qubits
if num_state_qubits is not None:
# set the new qubit registers
qr_state = QuantumRegister(num_state_qubits, name="state")
q_compare = QuantumRegister(1, name="compare")
self.qregs = [qr_state, q_compare]
# add ancillas is required
num_ancillas = num_state_qubits - 1
if num_ancillas > 0:
qr_ancilla = AncillaRegister(num_ancillas)
self.add_register(qr_ancilla)
def _get_twos_complement(self) -> list[int]:
"""Returns the 2's complement of ``self.value`` as array.
Returns:
The 2's complement of ``self.value``.
"""
twos_complement = pow(2, self.num_state_qubits) - int(np.ceil(self.value))
twos_complement = f"{twos_complement:b}".rjust(self.num_state_qubits, "0")
twos_complement = [
1 if twos_complement[i] == "1" else 0 for i in reversed(range(len(twos_complement)))
]
return twos_complement
def _check_configuration(self, raise_on_failure: bool = True) -> bool:
"""Check if the current configuration is valid."""
valid = True
if self._num_state_qubits is None:
valid = False
if raise_on_failure:
raise AttributeError("Number of state qubits is not set.")
if self._value is None:
valid = False
if raise_on_failure:
raise AttributeError("No comparison value set.")
required_num_qubits = 2 * self.num_state_qubits
if self.num_qubits != required_num_qubits:
valid = False
if raise_on_failure:
raise CircuitError("Number of qubits does not match required number of qubits.")
return valid
def _build(self) -> None:
qr_state = self.qubits[: self.num_state_qubits]
q_compare = self.qubits[self.num_state_qubits]
qr_ancilla = self.qubits[self.num_state_qubits + 1 :]
circuit = QuantumCircuit(*self.qregs, name=self.name)
if self.value <= 0: # condition always satisfied for non-positive values
if self._geq: # otherwise the condition is never satisfied
circuit.x(q_compare)
# condition never satisfied for values larger than or equal to 2^n
elif self.value < pow(2, self.num_state_qubits):
if self.num_state_qubits > 1:
twos = self._get_twos_complement()
for i in range(self.num_state_qubits):
if i == 0:
if twos[i] == 1:
circuit.cx(qr_state[i], qr_ancilla[i])
elif i < self.num_state_qubits - 1:
if twos[i] == 1:
circuit.compose(
OR(2), [qr_state[i], qr_ancilla[i - 1], qr_ancilla[i]], inplace=True
)
else:
circuit.ccx(qr_state[i], qr_ancilla[i - 1], qr_ancilla[i])
else:
if twos[i] == 1:
# OR needs the result argument as qubit not register, thus
# access the index [0]
circuit.compose(
OR(2), [qr_state[i], qr_ancilla[i - 1], q_compare], inplace=True
)
else:
circuit.ccx(qr_state[i], qr_ancilla[i - 1], q_compare)
# flip result bit if geq flag is false
if not self._geq:
circuit.x(q_compare)
# uncompute ancillas state
for i in reversed(range(self.num_state_qubits - 1)):
if i == 0:
if twos[i] == 1:
circuit.cx(qr_state[i], qr_ancilla[i])
else:
if twos[i] == 1:
circuit.compose(
OR(2), [qr_state[i], qr_ancilla[i - 1], qr_ancilla[i]], inplace=True
)
else:
circuit.ccx(qr_state[i], qr_ancilla[i - 1], qr_ancilla[i])
else:
# num_state_qubits == 1 and value == 1:
circuit.cx(qr_state[0], q_compare)
# flip result bit if geq flag is false
if not self._geq:
circuit.x(q_compare)
else:
if not self._geq: # otherwise the condition is never satisfied
circuit.x(q_compare)
self.append(circuit.to_gate(), self.qubits)