UUIDv8 Example

uuidv8_example.c

#include <stdint.h>
#include <time.h>

int get_random_bytes(uint8_t *buffer, int count);

int generate_uuidv8(uint8_t *uuid, uint8_t node_id) {
  struct timespec tp;
  if (clock_gettime(CLOCK_REALTIME, &tp) != 0)
    return -1; // real-time clock error

  // 32-bit biased timestamp (seconds elapsed since 2020-01-01 00:00:00 UTC)
  uint32_t timestamp_sec = tp.tv_sec - 1577836800;
  uuid[0] = timestamp_sec >> 24;
  uuid[1] = timestamp_sec >> 16;
  uuid[2] = timestamp_sec >> 8;
  uuid[3] = timestamp_sec;

  // 16-bit subsecond fraction (~15 microsecond resolution)
  uint16_t timestamp_subsec = ((uint64_t)tp.tv_nsec << 16) / 1000000000;
  uuid[4] = timestamp_subsec >> 8;
  uuid[5] = timestamp_subsec;

  // 58-bit random number and required ver and var fields
  if (get_random_bytes(&uuid[6], 8) != 0)
    return -1; // random number generator error
  uuid[6] = 0x80 | (uuid[6] & 0x0f);
  uuid[8] = 0x80 | (uuid[8] & 0x3f);

  // 8-bit application-specific node ID to guarantee application-wide uniqueness
  uuid[14] = node_id;

  // 8-bit rolling sequence number to help ensure process-wide uniqueness
  static uint8_t sequence = 0;
  uuid[15] = sequence++; // NOTE: unprotected from race conditions

  return 0;
}

#include <stdio.h>
#include <stdlib.h>

int get_random_bytes(uint8_t *buffer, int count) {
  arc4random_buf(buffer, count);
  return 0;
}

int main(void) {
  uint8_t uuid[16];
  for (int i = 0; i < 8; i++) {
    generate_uuidv8(uuid, 0x42);
    for (int i = 0; i < 16; i++) {
      printf("%02x", uuid[i]);
      if (i == 3 || i == 5 || i == 7 || i == 9)
        printf("-");
    }
    printf("\n");
  }
}