def _flash_encryption_tweak_range_bits(flash_crypt_config=15):
    """ Return bits (in reverse order) that the "key tweak" applies to,
    as determined by the FLASH_CRYPT_CONFIG 4 bit efuse value.
    """
    tweak_range = 0
    if flash_crypt_config & 1 != 0:
        tweak_range |= (
            115792089237316195422786347291764572757790510987739605737444789577355125325824
            )
    if flash_crypt_config & 2 != 0:
        tweak_range |= (
            784637716923335095458206029968399648046333517593518800896)
    if flash_crypt_config & 4 != 0:
        tweak_range |= 21267647932558653964155069955271819264
    if flash_crypt_config & 8 != 0:
        tweak_range |= 2305843009213693951
    return tweak_range
