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/*
* ulidgen_r - generate ULID
* (Universally Unique Lexicographically Sortable Identifier)
*
* To the extent possible under law, Leah Neukirchen <leah@vuxu.org>
* has waived all copyright and related or neighboring rights to this work.
* http://creativecommons.org/publicdomain/zero/1.0/
*/
#include <sys/random.h>
#include <stdint.h>
#include <stdlib.h>
#include <string.h>
#include <time.h>
void
ulidgen_r(char ulid[27])
{
static const char *b32alphabet = "0123456789ABCDEFGHJKMNPQRSTVWXYZ";
char *buf = ulid + 10;
int same = 1;
ulid[26] = 0;
struct timespec tv;
clock_gettime(CLOCK_REALTIME, &tv);
uint64_t t = tv.tv_sec*1000 + tv.tv_nsec/1000000;
for (int i = 9; i >= 0; i--, t /= 32)
if (ulid[i] != b32alphabet[t % 32])
ulid[i] = b32alphabet[t % 32], same = 0;
if (same) { /* increment random part in place */
int i = 15;
while (i >= 0 && buf[i] == 'Z')
buf[i--] = '0';
if (i < 0) {
/* restart 1ms + a bit later */
nanosleep(&(struct timespec) { 0, 1234567 }, 0);
ulidgen_r(ulid);
return;
}
char *s = strchr(b32alphabet, buf[i]);
if (s) {
buf[i] = *(s+1);
return;
}
/* else randomize again when we found invalid chars */
}
unsigned char rnd[16]; /* use 16 bytes for easier encoding */
if (getrandom(rnd, sizeof rnd, 0) < 0)
abort();
for (int i = 0; i < 16; i++)
buf[i] = b32alphabet[rnd[i] % 32];
}
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