CRC-16校验和实现

static const quint16 crc_tbl[16] = {
    0x0000, 0x1081, 0x2102, 0x3183,
    0x4204, 0x5285, 0x6306, 0x7387,
    0x8408, 0x9489, 0xa50a, 0xb58b,
    0xc60c, 0xd68d, 0xe70e, 0xf78f
};

enum ChecksumType {
    ChecksumIso3309,
    ChecksumItuV41
};

quint16 qChecksum(const char *data, uint len, Qt::ChecksumType standard)
{
    quint16 crc = 0x0000;
    switch (standard) {
    case Qt::ChecksumIso3309:
        crc = 0xffff;
        break;
    case Qt::ChecksumItuV41:
        crc = 0x6363;
        break;
    }
    uchar c;
    const uchar *p = reinterpret_cast<const uchar *>(data);
    while (len--) {
        c = *p++;
        crc = ((crc >> 4) & 0x0fff) ^ crc_tbl[((crc ^ c) & 15)];
        c >>= 4;
        crc = ((crc >> 4) & 0x0fff) ^ crc_tbl[((crc ^ c) & 15)];
    }
    switch (standard) {
    case Qt::ChecksumIso3309:
        crc = ~crc;
        break;
    case Qt::ChecksumItuV41:
        break;
    }
    return crc & 0xffff;
}