code: function padding(size,ch){
      var str = '';
      if(!ch && ch !== 0){
          ch = ' ';
      }
      while(size !== 0){
          if(size & 1 === 1){
              str += ch;
          }
          ch += ch;
          size >>>= 1;
      }
      return str;
  }
docs: return a string by repeat a char n times