code: public int getChunkId(byte[] key) {
          int idx = Arrays.binarySearch(maxKeyPerChunk, 0, filledUpTo + 1, key, comparator);
          idx = idx < 0 ? -idx - 1 : idx;
          if (idx > filledUpTo) {
              return -1;
          } else {
              return idx;
          }
      }
docs: returns the index of the chunk, where the element could be found. If the element can't be in one of the
  chunks the method will return -1.
  
  @param key
  the key to look for
  @return the id of the chunk, where the key could be found. If there is no putative chunk, then -1 will returned.