sclass LCSortedPairIndex {
  long[] pairs;
  int[] index;
  int ofs; // added to every result
  
  *(long[] pairs, int *ofs) {
    this(pairs);
  }
  
  *(long[] pairs) {
    this(pairs, null);
  }
  
  // primer is destroyed in the process
  *(long[] *pairs, LCSortedPairIndex primer) {
    int[] primerData = primer?.index;
    if (primer != null) primer.pairs = null;
    index = lc_sortedPairIndex(pairs, primerData);
  }
  
  int get(long pair) {
    int i = intArrayBinarySearchWithGeneralizedComparator(index, a -> {
      int x = cmp(pairs[a], pair);
      ifdef LCSortedPairIndex_debug
        printVars_str(+a, val := pairs[a], +pair, +x);
      endifdef
      ret x;
    });
    ret i >= 0 ? index[i]+ofs : -1;
  }
}