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SCRU128: Sortable, Clock and Random number-based Unique identifier

SCRU128 ID is yet another attempt to supersede UUID for the users who need decentralized, globally unique time-ordered identifiers. SCRU128 is inspired by ULID and KSUID and has the following features:

• 128-bit unsigned integer type
• Sortable by generation time (as integer and as text)
• 25-digit case-insensitive textual representation (Base36)
• 48-bit millisecond Unix timestamp that ensures useful life until year 10889
• Up to 281 trillion time-ordered but unpredictable unique IDs per millisecond
• 80-bit three-layer randomness for global uniqueness

#include "scru128.h"

#include <stdio.h>

int main() {
  Scru128Generator g;
  scru128_generator_init(&g);

  // generate a new identifier
  uint8_t x[16];
  scru128_generate(&g, x);
  char text[SCRU128_STR_LEN]; // 26 bytes
  scru128_to_str(x, text);
  puts(text); // e.g., "036z951mhjikzik2gsl81gr7l"

  // generate a textual representation directly
  scru128_generate_string(&g, text);
  puts(text); // e.g., "036z951mhzx67t63mq9xe6q0j"

  return 0;
}

See SCRU128 Specification for details.

Platform integration

scru128.h does not provide a concrete implementation of scru128_generate(), so users have to implement it to enable high-level generator APIs (if necessary) by integrating the low-level generator primitives provided by the library with the real-time clock and random number generator available in the system. Here is a quick example for the BSD-like systems:

#include "scru128.h"

#include <stdlib.h> // or <bsd/stdlib.h> on Linux with libbsd
#include <time.h>

int scru128_generate(Scru128Generator *g, uint8_t *id_out) {
  struct timespec tp;
  int err = clock_gettime(CLOCK_REALTIME, &tp);
  if (err) {
    return SCRU128_GENERATOR_STATUS_ERROR;
  }
  uint64_t timestamp = (uint64_t)tp.tv_sec * 1000 + tp.tv_nsec / 1000000;
  return scru128_generate_or_reset_core(g, id_out, timestamp, &arc4random,
                                        10000);
}

Find more examples in the platform directory.

License

Licensed under the Apache License, Version 2.0.

See also

• API reference for the list of provided functions