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.
node/etl/src/main/java/com/alibaba/otter/node/etl/common/io/signature/Crc32C.java