求教C语言编写的CRC16的校验程序

unsigned short crc_dsp(unsigned short reg, unsigned char data_crc) //reg为crc寄存器， data_crc为将要处理的8bit数据流 { unsigned short msb; //crc寄存器将移出的最高1bit unsigned short data; unsigned short gx = 0x8005, i = 0; //i为左移次数， gx为生成多项式