CAN的过滤器设置和移位

lanbeilu

u8  tempid = 0x00;
CAN_FilterInitStructure.CAN_FilterNumber=0;  
CAN_FilterInitStructure.CAN_FilterMode=CAN_FilterMode_IdMask;
 CAN_FilterInitStructure.CAN_FilterScale=CAN_FilterScale_32bit;

  CAN_FilterInitStructure.CAN_FilterIdHigh = (tempid & 0x003f)<<3; //根据目标地址接收
  CAN_FilterInitStructure.CAN_FilterIdLow = ((u16)1<<2); 
  CAN_FilterInitStructure.CAN_FilterMaskIdHigh = 0xfff8;
  CAN_FilterInitStructure.CAN_FilterMaskIdLow = ((u16)1<<2)|((u16)1<<1);
对于过滤器配置的这些移位不理解？求助