From 8c25d12ae51798abd2f1ca2247c63b7c6b01fb25 Mon Sep 17 00:00:00 2001
From: Leandro Lanzieri <leandro.lanzieri@haw-hamburg.de>
Date: Mon, 27 Jan 2020 17:05:22 +0100
Subject: [PATCH] net/coap: Represent `ACK_RANDOM_FACTOR` multiplied by 1000

---
 sys/include/net/coap.h | 17 +++++++++++++----
 1 file changed, 13 insertions(+), 4 deletions(-)

diff --git a/sys/include/net/coap.h b/sys/include/net/coap.h
index 894c019f8b..6d8fe43b6b 100644
--- a/sys/include/net/coap.h
+++ b/sys/include/net/coap.h
@@ -178,15 +178,24 @@ extern "C" {
  * This value is for the response to the *initial* confirmable message. The
  * timeout doubles for subsequent retries. To avoid synchronization of resends
  * across hosts, the actual timeout is chosen randomly between
- * @ref COAP_ACK_TIMEOUT and (@ref COAP_ACK_TIMEOUT * @ref COAP_RANDOM_FACTOR).
+ * @ref COAP_ACK_TIMEOUT and
+ * (@ref COAP_ACK_TIMEOUT * @ref COAP_RANDOM_FACTOR_1000 / 1000).
  */
 #ifndef COAP_ACK_TIMEOUT
 #define COAP_ACK_TIMEOUT        (2U)
 #endif
 
-/** @brief   Used to calculate upper bound for timeout; see @ref COAP_ACK_TIMEOUT */
-#ifndef COAP_RANDOM_FACTOR
-#define COAP_RANDOM_FACTOR      (1.5)
+/**
+ * @brief   Used to calculate upper bound for timeout
+ *
+ * This represents the `ACK_RANDOM_FACTOR`
+ * ([RFC 7252, section 4.2](https://tools.ietf.org/html/rfc7252#section-4.2))
+ * multiplied by 1000, to avoid floating point arithmetic.
+ *
+ * See @ref COAP_ACK_TIMEOUT
+ */
+#ifndef COAP_RANDOM_FACTOR_1000
+#define COAP_RANDOM_FACTOR_1000      (1500)
 #endif
 
 /**