docs: protected Digest copyState(DigestEngine dest) {
          dest.inputLen = inputLen;
          dest.blockCount = blockCount;
          System.arraycopy(inputBuf, 0, dest.inputBuf, 0, inputBuf.length);
          adjustDigestLen();
          dest.adjustDigestLen();
          System.arraycopy(outputBuf, 0, dest.outputBuf, 0, outputBuf.length);
          return dest;
      }