_constantmath.py 文件源码

def mul_by_constant_modN(eng, c, N, quint_in):
    """
    Multiplies a quantum integer by a classical number a modulo N, i.e.,

    |x> -> |a*x mod N>

    (only works if a and N are relative primes, otherwise the modular inverse
    does not exist).
    """
    assert(c < N and c >= 0)
    assert(gcd(c, N) == 1)

    n = len(quint_in)
    quint_out = eng.allocate_qureg(n + 1)

    for i in range(n):
        with Control(eng, quint_in[i]):
            AddConstantModN((c << i) % N, N) | quint_out

    for i in range(n):
        Swap | (quint_out[i], quint_in[i])

    cinv = inv_mod_N(c, N)

    for i in range(n):
        with Control(eng, quint_in[i]):
            SubConstantModN((cinv << i) % N, N) | quint_out
    del quint_out


# calculates the inverse of a modulo N