#include <stdint.h>

#include <stdio.h>

#include <stdlib.h>

#include <time.h>

#include <unistd.h>

int uuidv7(uint8_t* value) {

// random bytes

int err = getentropy(value, 16);

if (err != EXIT_SUCCESS) {

return EXIT_FAILURE;

}

// current timestamp in ms

struct timespec ts;

int ok = timespec_get(&ts, TIME_UTC);

if (ok == 0) {

return EXIT_FAILURE;

}

uint64_t timestamp = (uint64_t)ts.tv_sec * 1000 + ts.tv_nsec / 1000000;

// timestamp

value[0] = (timestamp >> 40) & 0xFF;

value[1] = (timestamp >> 32) & 0xFF;

value[2] = (timestamp >> 24) & 0xFF;

value[3] = (timestamp >> 16) & 0xFF;

value[4] = (timestamp >> 8) & 0xFF;

value[5] = timestamp & 0xFF;

// version and variant

value[6] = (value[6] & 0x0F) | 0x70;

value[8] = (value[8] & 0x3F) | 0x80;

return EXIT_SUCCESS;

}

int main() {

uint8_t uuid_val[16];

uuidv7(uuid_val);

for (size_t i = 0; i < 16; i++) {

printf("%02x", uuid_val[i]);

}

printf("\n");

}