Hopefully correct code for C's strict aliasing rules

[proxmark3-svn] / common / iso14443_crc.c

//-----------------------------------------------------------------------------\r
// Routines to compute the CRCs (two different flavours, just for confusion)\r
// required for ISO 14443, swiped directly from the spec.\r
//-----------------------------------------------------------------------------\r
\r
#define	CRC_14443_A	0x6363	/* ITU-V.41 */\r
#define	CRC_14443_B	0xFFFF  /* ISO/IEC 13239 (formerly ISO/IEC 3309) */\r
\r
static unsigned short UpdateCrc14443(unsigned char ch, unsigned short *lpwCrc)\r
{\r
    ch = (ch ^ (unsigned char) ((*lpwCrc) & 0x00FF));\r
    ch = (ch ^ (ch << 4));\r
    *lpwCrc =	(*lpwCrc >> 8) ^ ((unsigned short) ch << 8) ^\r
            	((unsigned short) ch << 3) ^ ((unsigned short) ch >> 4);\r
    return (*lpwCrc);\r
}\r
\r
static void ComputeCrc14443(int CrcType, BYTE *Data, int Length,\r
           BYTE *TransmitFirst, BYTE *TransmitSecond)\r
{\r
    unsigned char chBlock;\r
    unsigned short wCrc=CrcType;\r
\r
	do {\r
        chBlock = *Data++;\r
        UpdateCrc14443(chBlock, &wCrc);\r
    } while (--Length);\r
\r
    if (CrcType == CRC_14443_B)\r
        wCrc = ~wCrc;                /* ISO/IEC 13239 (formerly ISO/IEC 3309) */\r
\r
    *TransmitFirst = (BYTE) (wCrc & 0xFF);\r
    *TransmitSecond = (BYTE) ((wCrc >> 8) & 0xFF);\r
    return;\r
}\r