docs: public static int bestBufferSize( long fileSize ) {
          assert fileSize >= 0;
          if (fileSize < TINY_FILE_SIZE) {
              return (int)fileSize + 2;
          }
          if (fileSize < SMALL_FILE_SIZE) {
              return TINY_BUFFER_SIZE;
          }
          if (fileSize < MEDIUM_FILE_SIZE) {
              return SMALL_BUFFER_SIZE;
          }
          if (fileSize < LARGE_SIZE) {
              return MEDIUM_BUFFER_SIZE;
          }
          return LARGE_BUFFER_SIZE;
      }