notes

#define AP_KEY_STRING_LEN 68



// PLEASE, do not copy&paste this function into keygen code :)
static inline bool KeyCheckStringCrc(const utf16_t* str)
{
    size_t len = utf16len(str);

    if (len != AP_KEY_STRING_LEN )
    {
        return false;
    }

    uint16_t crc=0;

    for (unsigned int i=0;i<(AP_KEY_STRING_LEN-2);i++)
    {
        if ( (i>=2) && (KeyIsValidChar(str[i])==false)) return false;

        crc += ((uint8_t)str[i]) & 0x7f;

        crc = (uint16_t) (((crc*(11+i)))%4093);
    }

    if (KeyBitsToChar( (uint8_t) (crc&0x3f) ) != str[AP_KEY_STRING_LEN-2]) return false;
    if (KeyBitsToChar( (uint8_t) ((crc>>6)&0x3f)) != str[AP_KEY_STRING_LEN-1]) return false;

    return true;
}


static inline char KeyBitsToChar(uint8_t c)
{
    if (c==0) return '_';
    if (c<11) return '0' + (c-1);
    if (c<38) return '@'+(c-11);
    return 'a'+(c-38);
}

static inline uint8_t KeyIsValidChar(utf16_t c)
{
    if (c=='_') return true;
    if ( (c>='0') && (c<='9') ) return true;
    if ( (c>='@') && (c<='Z') ) return true;
    if ( (c>='a') && (c<='z') ) return true;
    return false;
}