ipv6/addr: initialize iid part of an ipv6 address

sys/include/net/ipv6/addr.h

@@ -470,6 +470,17 @@ uint8_t ipv6_addr_match_prefix(const ipv6_addr_t *a, const ipv6_addr_t *b);
  */
 void ipv6_addr_init_prefix(ipv6_addr_t *out, const ipv6_addr_t *prefix, uint8_t bits);
 
+/**
+ * @brief   Sets the last @p bits of IPv6 address @p out to @p iid.
+ *          Leading bits of @p out stay untouched.
+ *
+ * @param[out]  out     IPv6 address to be set.
+ * @param[in]   iid     buffer representing the iid.
+ * @param[in]   bits    Bits to be copied from @p iid to @p out
+ *                      (set to 128 when greater than 128).
+ */
+void ipv6_addr_init_iid(ipv6_addr_t *out, const uint8_t *iid, uint8_t bits);
+
 /**
  * @brief   Sets @p addr dynamically to the unspecified IPv6 address (::).
  *

sys/net/network_layer/ipv6/addr/ipv6_addr.c

@@ -77,6 +77,29 @@ void ipv6_addr_init_prefix(ipv6_addr_t *out, const ipv6_addr_t *prefix,
         out->u8[bytes] |= (prefix->u8[bytes] & mask);
     }
 }
+
+void ipv6_addr_init_iid(ipv6_addr_t *out, const uint8_t *iid, uint8_t bits)
+{
+    uint8_t unaligned_bits, bytes, pos;
+
+    if (bits > 128) {
+        bits = 128;
+    }
+
+    unaligned_bits = bits % 8;
+    bytes = bits / 8;
+    pos = (IPV6_ADDR_BIT_LEN / 8) - bytes;
+
+    if (unaligned_bits) {
+        uint8_t mask = 0xff << unaligned_bits;
+        out->u8[pos - 1] &= mask;
+        out->u8[pos - 1] |= (*iid & ~mask);
+        iid++;
+    }
+
+    memcpy(&(out->u8[pos]), iid, bytes);
+}
+
 /**
  * @}
  */