Canonical way / best practice for 128-bit integers

Hello,

I’m working on some bluetooth code, and that involves handling 128-bit uuids.
There are various ways to handle in the FreeBSD codebase, like in sdp.h:

/*
 * SDP int128/uint128 parameter
 */
    
struct int128 {
        int8_t  b[16];
};
typedef struct int128   int128_t;
typedef struct int128   uint128_t;

and in sys/dev/random/uint128.h

#ifdef USE_REAL_UINT128_T
typedef __uint128_t uint128_t;
#define UINT128_ZERO 0ULL
#else
typedef struct {
        /* Ignore endianness */
        uint64_t u128t_word0;
        uint64_t u128t_word1;
} uint128_t;
static const uint128_t very_long_zero = {0UL,0UL};
#define UINT128_ZERO very_long_zero
#endif

Is there any recommended / standard way to handle 128 bit integers in a portable way?

Best regards,

Marc Veldman