Add a few functions to do unaligned access.

Add a few functions to read 16bits and 32bits integers that may be
unaligned, both in host and network order.

include/common/net_helper.h

@@ -0,0 +1,75 @@
+/*
+ * include/common/net_helper.h
+ * This file contains miscellaneous network helper functions.
+ *
+ * Copyright (C) 2017 Olivier Houchard
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+ * SOFTWARE.
+ */
+
+#ifndef _COMMON_NET_HELPER_H
+#define _COMMON_NET_HELPER_H
+
+#include <arpa/inet.h>
+
+/* Functions to read various integer that may be unaligned */
+
+/* Read a uint16_t */
+uint16_t readu16(const void *p)
+{
+        const union {  uint16_t u16; } __attribute__((packed))*u = p;
+        return u->u16;
+}
+
+/* Read a int16_t */
+int16_t readi16(const void *p)
+{
+        const union {  int16_t i16; } __attribute__((packed))*u = p;
+        return u->i16;
+}
+
+/* Read a uint16_t, and convert from network order to host order */
+uint16_t readn16(const void *p)
+{
+        const union {  uint16_t u16; } __attribute__((packed))*u = p;
+        return ntohs(u->u16);
+}
+
+/* Read a uint32_t */
+uint32_t readu32(const void *p)
+{
+        const union {  uint32_t u32; } __attribute__((packed))*u = p;
+        return u->u32;
+}
+
+/* Read a int32_t */
+int16_t readi32(const void *p)
+{
+        const union {  int32_t i32; } __attribute__((packed))*u = p;
+        return u->i32;
+}
+
+/* Read a uint32_t, and convert from network order to host order */
+uint32_t readn32(const void *p)
+{
+        const union {  uint32_t u32; } __attribute__((packed))*u = p;
+        return ntohl(u->u32);
+}
+
+#endif /* COMMON_NET_HELPER_H */