From 747bf5bf77512daeac551a762f6a7669769f6ca1 Mon Sep 17 00:00:00 2001
From: Josef 'Jeff' Sipek <jeff.sipek@dovecot.fi>
Date: Mon, 18 Sep 2017 13:55:08 +0300
Subject: [PATCH] lib: introduce i_rand_limit() and i_rand_minmax()

---
 src/lib/lib.h  |  9 +++++++++
 src/lib/rand.c | 11 +++++++++++
 2 files changed, 20 insertions(+)

diff --git a/src/lib/lib.h b/src/lib/lib.h
index e795101e4d..a02fbb1f7c 100644
--- a/src/lib/lib.h
+++ b/src/lib/lib.h
@@ -90,5 +90,14 @@ bool lib_is_initialized(void);
 void lib_deinit(void);
 
 uint32_t i_rand(void);
+/* Returns a random integer < upper_bound. */
+uint32_t i_rand_limit(uint32_t upper_bound);
+
+/* Returns a random integer >= min_val, and <= max_val. */
+static inline uint32_t i_rand_minmax(uint32_t min_val, uint32_t max_val)
+{
+	i_assert(min_val <= max_val);
+	return min_val + i_rand_limit(max_val - min_val + 1);
+}
 
 #endif
diff --git a/src/lib/rand.c b/src/lib/rand.c
index 781a38f6bc..e9f3cfad7a 100644
--- a/src/lib/rand.c
+++ b/src/lib/rand.c
@@ -12,6 +12,11 @@ uint32_t i_rand(void)
 {
 	return arc4random();
 }
+
+uint32_t i_rand_limit(uint32_t upper_bound)
+{
+	return arc4random_uniform(upper_bound);
+}
 #else
 uint32_t i_rand(void)
 {
@@ -19,4 +24,10 @@ uint32_t i_rand(void)
 	random_fill(&value, sizeof(value));
 	return value;
 }
+
+uint32_t i_rand_limit(uint32_t upper_bound)
+{
+	/* FIXME: This simple implementation suffers from modulo-bias. */
+	return i_rand() % upper_bound;
+}
 #endif
-- 
2.47.3