public static int unmask(int maskedCrc) {
        int rot = maskedCrc - MASK_DELTA;
        return ((rot >>> 17) | (rot << 15));
    }
Return the crc whose masked representation is masked_crc.
codec/codec-api/src/main/java/com/alipay/sofa/rpc/codec/snappy/Crc32C.java