code: protected final int getRawOffset(int offset, char ch)
      {
          return (m_index_[offset + (ch >> INDEX_STAGE_1_SHIFT_)]
                  << INDEX_STAGE_2_SHIFT_)
                  + (ch & INDEX_STAGE_3_MASK_);
      }
docs: Gets the offset to the data which the index ch after variable offset
  points to.
  Note for locating a non-supplementary character data offset, calling
  <p>
  getRawOffset(0, ch);
  </p>
  will do. Otherwise if it is a supplementary character formed by
  surrogates lead and trail. Then we would have to call getRawOffset()
  with getFoldingIndexOffset(). See getSurrogateOffset().
  @param offset index offset which ch is to start from
  @param ch index to be used after offset
  @return offset to the data