function indexBig5PointerFor(code_point) {
    // 1. Let index be index Big5 excluding all entries whose pointer
    big5_index_no_hkscs = big5_index_no_hkscs ||
      index('big5').map(function(code_point, pointer) {
        return (pointer < (0xA1 - 0x81) * 157) ? null : code_point;
      });
    var index_ = big5_index_no_hkscs;

    // 2. If code point is U+2550, U+255E, U+2561, U+256A, U+5341, or
    // U+5345, return the last pointer corresponding to code point in
    // index.
    if (code_point === 0x2550 || code_point === 0x255E ||
        code_point === 0x2561 || code_point === 0x256A ||
        code_point === 0x5341 || code_point === 0x5345) {
      return index_.lastIndexOf(code_point);
    }

    // 3. Return the index pointer for code point in index.
    return indexPointerFor(code_point, index_);
  }
@param {number} code_point The |code_point| to search for in the big5
    index.
@return {?number} The code point corresponding to |pointer| in |index|,
    or null if |code point| is not in the big5 index.