private int approximateBinarySearch(long searchX,int startSearchIndex,boolean preferStart){
  return approximateBinarySearch(searchX,startSearchIndex,mData.size() - 1,preferStart,DEFAULT_APPROX_RANGE);
}

private int approximateBinarySearch ( long searchX , int startSearchIndex , boolean preferStart ) { return approximateBinarySearch ( searchX , startSearchIndex , mData . size ( ) - 1 , preferStart , DEFAULT_APPROX_RANGE ) ; }
a helper function to search for the index of the point with the closest value to the searchx provided , using the default approximate search range .
