Get __uint128_t integer from UUID string (tested on clang-1403.0.22.14.1)

get128FromUUID.c

__uint128_t get128FromUUID(const char* uuid) {
    __uint128_t result = 0;
    unsigned char currentData, dashcnt = 0;
    
    if(uuid[36] != 0x00)
        return (__uint128_t)0xf << 124; // length mismatch
    for(unsigned char i=0;i<36;i++) {
        if(uuid[i] >= 0x30 && uuid[i] <= 0x39) currentData = uuid[i] - 0x30; // Numberic digit
        else if(uuid[i] >= 0x41 && uuid[i] <= 0x46) currentData = 10 + uuid[i] - 0x41; // Capital letter digit
        else if(uuid[i] >= 0x61 && uuid[i] <= 0x66) currentData = 10 + uuid[i] - 0x61; // small letter digit
        else if(uuid[i] == '-') {dashcnt++; continue;} // dash
        else continue; // undefined behavior
        result |= ((__uint128_t)currentData) << 4*(31-i+dashcnt);
    }
    return result;
}