code: func (iter *Iterator) ReadInt64() (ret int64) {
  	c := iter.nextToken()
  	if c == '-' {
  		val := iter.readUint64(iter.readByte())
  		if val > math.MaxInt64+1 {
  			iter.ReportError("ReadInt64", "overflow: "+strconv.FormatUint(uint64(val), 10))
  			return
  		}
  		return -int64(val)
  	}
  	val := iter.readUint64(c)
  	if val > math.MaxInt64 {
  		iter.ReportError("ReadInt64", "overflow: "+strconv.FormatUint(uint64(val), 10))
  		return
  	}
  	return int64(val)
  }
docs: // ReadInt64 read int64