1 files changed, 61 insertions, 0 deletions
diff --git a/ulid.c b/ulid.c
new file mode 100644
index 0000000..dde7add
--- /dev/null
+++ b/ulid.c
@@ -0,0 +1,61 @@
+/*
+ * 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];
+}