快速CRC16-CCITT算法，速度与查表法相当

只看该作者 · 2011-6-1 01:58

下面是针对IAR EWAVR的内联汇编优化代码，包含C代码。
如果使用C的话，需要针对使用的MCU和编译器作些优化。

//
// for iar ewavr
//
//----------------------------------------------------------------------------------------------
//
// CRC16-CCITT(ITU), 多项式: x16+x12+x5+1, LSB右移(0x8408).
//
unsigned short crc16_itu_lsb( unsigned short crc, unsigned int len, unsigned char *data )
{
// unsigned char temp;
// while(len--)
// {
//       temp = crc ^ *data++;
//       temp ^= temp<<4;
//       crc = (crc>>8) ^ (temp<<3) ^ (temp<<8) ^ (temp>>4);
// }
// return crc;
__asm ( " MOVW R30, R20          \n" // R21:R20 = unsigned char *data
         " LDI    R20, 1<<4          \n"
         " RJMP crc16_itu_lsb_while \n"
         "crc16_itu_lsb_do:             \n"
//       temp = crc ^ *data++;
         " LD    R0, Z+             \n"
         " EOR    R16, R0          \n" // R16 = crc^*data
//       temp ^= temp<<4;
         " MUL    R16, R20          \n" // R0  = temp<<4
         " EOR    R16, R0          \n" // R16 = temp^(temp<<4)
//       crc = (crc>>8) ^ (temp<<3) ^ (temp<<8) ^ (temp>>4);
         " MUL    R16, R20          \n" // R1:R0 = temp<<4
         " EOR    R17, R1          \n" // R17 = (crc>>8)^(temp>>4)
         " LSR    R1                \n"
         " ROR    R0                \n" // R1:R0 = temp<<3
         " EOR    R0, R17          \n" // R0  = crc_l
         " EOR    R1, R16          \n" // R1  = crc_h
         " MOVW R16, R0          \n" // R17:R16 = unsigned short crc
         "crc16_itu_lsb_while:          \n"
         " SUBI R18, 1             \n" // R19:R18 = unsigned int len
         " SBCI R19, 0             \n"
         " BRCC crc16_itu_lsb_do \n"
      );
return crc;
}
//----------------------------------------------------------------------------------------------
//
// CRC16-CCITT(ITU), 多项式: x16+x12+x5+1, MSB左移(0x1021).
//
unsigned short crc16_itu_msb( unsigned short crc, unsigned int len, unsigned char *data )
{
// unsigned char temp;
// while(len--)
// {
//       temp = (crc>>8) ^ *data++;
//       temp ^= temp>>4;
//       crc = (crc<<8) ^ (temp<<5) ^ (temp<<0) ^ (temp<<12);
// }
// return crc;
__asm ( " MOVW R30, R20          \n" // R21:R20 = unsigned char *data
         " LDI    R20, 1<<4          \n"
         " RJMP crc16_itu_msb_while \n"
         "crc16_itu_msb_do:             \n"
//       temp = (crc>>8) ^ *data++;
         " LD    R0, Z+             \n"
         " EOR    R17, R0          \n" // R17 = (crc>>8)^*data
//       temp ^= temp>>4;
         " MUL    R17, R20          \n" // R1  = temp>>4
         " EOR    R17, R1          \n" // R17 = temp^(temp>>4)
//       crc = (crc<<8) ^ (temp<<5) ^ (temp<<0) ^ (temp<<12);
         " MUL    R17, R20          \n" // R1:R0 = temp<<4
         " EOR    R16, R0          \n" // R16 = (crc<<8)^(temp<<12)
         " LSL    R0                \n"
         " ROL    R1                \n" // R1:R0 = temp<<5
         " EOR    R0, R17          \n" // R0  = crc_l
         " EOR    R1, R16          \n" // R1  = crc_h
         " MOVW R16, R0          \n" // R17:R16 = unsigned short crc
         "crc16_itu_msb_while:          \n"
         " SUBI R18, 1             \n" // R19:R18 = unsigned int len
         " SBCI R19, 0             \n"
         " BRCC crc16_itu_msb_do \n"
      );
return crc;
}