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109 lines
3.2 KiB
Python
109 lines
3.2 KiB
Python
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# https://github.com/rupansh/QuantumComputing/blob/master/rippleadd.py
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# https://en.wikipedia.org/wiki/Adder_(electronics)#Full_adder
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# https://en.wikipedia.org/wiki/Controlled_NOT_gate
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from qiskit import Aer, QuantumCircuit, execute
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from qiskit.providers import BaseBackend
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def store_two_classics(val1: int, val2: int) -> (QuantumCircuit, str, str):
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"""
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Generates a Quantum Circuit which stores two classical integers
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Returns the circuit and binary representation of the integers
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"""
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x, y = bin(val1)[2:], bin(val2)[2:] # Remove leading '0b'
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# Ensure that both strings are of the same length
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if len(x) > len(y):
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y = y.zfill(len(x))
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else:
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x = x.zfill(len(y))
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# We need (3 * number of bits in the larger number)+1 qBits
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# The second parameter is the number of classical registers, to measure the result
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circuit = QuantumCircuit((len(x) * 3) + 1, len(x) + 1)
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# We are essentially "not-ing" the bits that are 1
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# Reversed because its easier to perform ops on more significant bits
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for i in range(len(x)):
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if x[::-1][i] == "1":
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circuit.x(i)
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for j in range(len(y)):
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if y[::-1][j] == "1":
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circuit.x(len(x) + j)
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return circuit, x, y
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def full_adder(
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circuit: QuantumCircuit,
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input1_loc: int,
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input2_loc: int,
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carry_in: int,
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carry_out: int,
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):
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"""
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Quantum Equivalent of a Full Adder Circuit
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CX/CCX is like 2-way/3-way XOR
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"""
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circuit.ccx(input1_loc, input2_loc, carry_out)
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circuit.cx(input1_loc, input2_loc)
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circuit.ccx(input2_loc, carry_in, carry_out)
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circuit.cx(input2_loc, carry_in)
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circuit.cx(input1_loc, input2_loc)
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def ripple_adder(
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val1: int, val2: int, backend: BaseBackend = Aer.get_backend("qasm_simulator")
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) -> int:
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"""
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Quantum Equivalent of a Ripple Adder Circuit
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Uses qasm_simulator backend by default
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Currently only adds 'emulated' Classical Bits
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but nothing prevents us from doing this with hadamard'd bits :)
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Only supports adding +ve Integers
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>>> ripple_adder(3, 4)
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7
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>>> ripple_adder(10, 4)
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14
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>>> ripple_adder(-1, 10)
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Traceback (most recent call last):
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...
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ValueError: Both Integers must be positive!
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"""
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if val1 < 0 or val2 < 0:
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raise ValueError("Both Integers must be positive!")
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# Store the Integers
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circuit, x, y = store_two_classics(val1, val2)
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"""
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We are essentially using each bit of x & y respectively as full_adder's input
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the carry_input is used from the previous circuit (for circuit num > 1)
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the carry_out is just below carry_input because
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it will be essentially the carry_input for the next full_adder
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"""
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for i in range(len(x)):
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full_adder(circuit, i, len(x) + i, len(x) + len(y) + i, len(x) + len(y) + i + 1)
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circuit.barrier() # Optional, just for aesthetics
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# Measure the resultant qBits
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for i in range(len(x) + 1):
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circuit.measure([(len(x) * 2) + i], [i])
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res = execute(circuit, backend, shots=1).result()
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# The result is in binary. Convert it back to int
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return int(list(res.get_counts().keys())[0], 2)
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if __name__ == "__main__":
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import doctest
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doctest.testmod()
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