1 files changed, 48 insertions, 0 deletions
diff --git a/src/lib/primes.c b/src/lib/primes.c
new file mode 100644
index 0000000..cb4a5e2
--- /dev/null
+++ b/src/lib/primes.c
@@ -0,0 +1,48 @@
+/* Copyright (c) 2013-2018 Dovecot authors, see the included COPYING file */
+
+#include "lib.h"
+#include "primes.h"
+
+static const unsigned int primes[] = {
+#define PRIME_SKIP_COUNT 3
+	17,
+	37,
+	67,
+	131,
+	257, /* next from 2^8 */
+	521,
+	1031,
+	2053,
+	4099,
+	8209,
+	16411,
+	32771,
+	65537, /* next from 2^16 */
+	131101,
+	262147,
+	524309,
+	1048583,
+	2097169,
+	4194319,
+	8388617,
+	16777259, /* next from 2^24 */
+	33554467,
+	67108879,
+	134217757,
+	268435459,
+	536870923,
+	1073741827,
+	2147483659U,
+	4294967291U /* previous from 2^32 */
+};
+
+unsigned int primes_closest(unsigned int num)
+{
+	unsigned int i;
+
+	for (i = 31; i > PRIME_SKIP_COUNT; i--) {
+		if ((num & (1U << i)) != 0)
+			return primes[i - PRIME_SKIP_COUNT];
+	}
+	return primes[0];
+}