static __inline__ uint16_t _crc_xmodem

static __inline__ uint16_t _crc_xmodem_update(uint16_t __crc, uint8_t __data)

Optimized CRC-XMODEM calculation.

Polynomial: x^16 + x^12 + x^5 + 1 (0x1021) Initial value: 0x0

This is the CRC used by the Xmodem-CRC protocol.

The following is the equivalent functionality written in C.

    uint16_t
    crc_xmodem_update (uint16_t crc, uint8_t data)
    {
        int i;

        crc = crc ^ ((uint16_t)data << 8);
        for (i=0; i<8; i++)
        {
            if (crc & 0x8000)
                crc = (crc << 1) ^ 0x1021;
            else
                crc <<= 1;
        }

        return crc;
    }