def _const_compare_digest_backport(a, b):
    """
    Compare two digests of equal length in constant time.

    The digests must be of type str/bytes.
    Returns True if the digests match, and False otherwise.
    """
    result = abs(len(a) - len(b))
    for l, r in zip(bytearray(a), bytearray(b)):
        result |= l ^ r
    return result == 0
