From d7943a49aa9e849441197c5612910dcf301392e4 Mon Sep 17 00:00:00 2001
From: Benjamin Valentin <benjamin.valentin@ml-pa.com>
Date: Wed, 30 Sep 2020 11:16:47 +0200
Subject: [PATCH 1/2] net/eui48: reorder code

Move eui48_set_local() and eui48_clear_group() to the top so we can
use it later in the file.
---
 sys/include/net/eui48.h | 87 ++++++++++++++++++++---------------------
 1 file changed, 43 insertions(+), 44 deletions(-)

diff --git a/sys/include/net/eui48.h b/sys/include/net/eui48.h
index 2a5fadfa9300..5dcbbf29b27a 100644
--- a/sys/include/net/eui48.h
+++ b/sys/include/net/eui48.h
@@ -36,6 +36,49 @@ typedef struct {
     uint8_t uint8[6];            /**< split into 6 8-bit words. */
 } eui48_t;
 
+/**
+ * @name EUI-48 bit flags contained in the first octet
+ *
+ * @see IEEE 802-2001 section 9.2
+ * @{
+ */
+
+/**
+ * @brief Locally administered address.
+ */
+#define EUI48_LOCAL_FLAG    0x02
+
+/**
+ * @brief Group type address.
+ */
+#define EUI48_GROUP_FLAG    0x01
+/** @} */
+
+/**
+ * @brief Set the locally administrated bit in the EUI-48 address.
+ *
+ * @see IEEE 802-2001 section 9.2
+ *
+ * @param   addr    ethernet address
+ */
+static inline void eui48_set_local(eui48_t *addr)
+{
+    addr->uint8[0] |= EUI48_LOCAL_FLAG;
+}
+
+/**
+ * @brief Clear the group address bit to signal the address as individual
+ * address
+ *
+ * @see IEEE 802-2001 section 9.2
+ *
+ * @param   addr    ethernet address
+ */
+static inline void eui48_clear_group(eui48_t *addr)
+{
+    addr->uint8[0] &= ~EUI48_GROUP_FLAG;
+}
+
 /**
  * @brief   Generates an EUI-64 from a 48-bit device address
  *
@@ -56,24 +99,6 @@ static inline void eui48_to_eui64(eui64_t *eui64, const eui48_t *addr)
     eui64->uint8[7] = addr->uint8[5];
 }
 
-/**
- * @name EUI-48 bit flags contained in the first octet
- *
- * @see IEEE 802-2001 section 9.2
- * @{
- */
-
-/**
- * @brief Locally administered address.
- */
-#define EUI48_LOCAL_FLAG  0x02
-
-/**
- * @brief Group type address.
- */
-#define EUI48_GROUP_FLAG        0x01
-/** @} */
-
 /**
  * @brief   Generates an IPv6 interface identifier from a 48-bit device address
  *
@@ -106,32 +131,6 @@ static inline void eui48_from_ipv6_iid(eui48_t *addr, const eui64_t *iid)
     addr->uint8[5] = iid->uint8[7];
 }
 
-/**
- * @brief Set the locally administrated bit in the EUI-48 address.
- *
- * @see IEEE 802-2001 section 9.2
- *
- * @param   addr    ethernet address
- */
-static inline void eui48_set_local(eui48_t *addr)
-{
-    addr->uint8[0] |= EUI48_LOCAL_FLAG;
-}
-
-/**
- * @brief Clear the group address bit to signal the address as individual
- * address
- *
- * @see IEEE 802-2001 section 9.2
- *
- * @param   addr    ethernet address
- */
-static inline void eui48_clear_group(eui48_t *addr)
-{
-    addr->uint8[0] &= ~EUI48_GROUP_FLAG;
-}
-
-
 #ifdef __cplusplus
 }
 #endif

From 307ea6224a38fc44bf667b3758ac5bba6dcebb4d Mon Sep 17 00:00:00 2001
From: Benjamin Valentin <benjamin.valentin@ml-pa.com>
Date: Wed, 30 Sep 2020 11:17:53 +0200
Subject: [PATCH 2/2] net/eui48: add eui64_to_eui48()

Provide helper function to mangle a EUI-64 into an EUI-48.
This can be useful to get predictable, locally unique addreses.
---
 sys/include/net/eui48.h | 25 +++++++++++++++++++++++++
 1 file changed, 25 insertions(+)

diff --git a/sys/include/net/eui48.h b/sys/include/net/eui48.h
index 5dcbbf29b27a..50dd310afc81 100644
--- a/sys/include/net/eui48.h
+++ b/sys/include/net/eui48.h
@@ -99,6 +99,31 @@ static inline void eui48_to_eui64(eui64_t *eui64, const eui48_t *addr)
     eui64->uint8[7] = addr->uint8[5];
 }
 
+/**
+ * @brief   Generates an EUI-48 from a 64-bit device address
+ *
+ * @warning The resulting EUI-48 is not guaranteed to be unique
+ *          and, hence, marked as only locally unique.
+ *
+ * @param[out] eui48    the resulting EUI-48.
+ * @param[in]  addr     a 64-bit device address
+ */
+static inline void eui64_to_eui48(eui48_t *eui48, const eui64_t *addr)
+{
+    /* Preserve vendor id */
+    eui48->uint8[0] = addr->uint8[0];
+    eui48->uint8[1] = addr->uint8[1];
+    eui48->uint8[2] = addr->uint8[2];
+
+    /* Use most volatile bits */
+    eui48->uint8[3] = addr->uint8[5];
+    eui48->uint8[4] = addr->uint8[6];
+    eui48->uint8[5] = addr->uint8[7];
+
+    /* EUI is only locally unique */
+    eui48_set_local(eui48);
+}
+
 /**
  * @brief   Generates an IPv6 interface identifier from a 48-bit device address
  *