1 files changed, 44 insertions, 0 deletions
diff --git a/src/pcap_layers/byteorder.h b/src/pcap_layers/byteorder.h
new file mode 100644
index 0000000..720a516
--- /dev/null
+++ b/src/pcap_layers/byteorder.h
@@ -0,0 +1,44 @@
+#ifndef BYTEORDER_H
+#define BYTEORDER_H
+
+/* The following macros are similar to [nh]to[hn][ls](), except that the
+ * network-ordered integer is referred to by a pointer, and does not need to
+ * be aligned.  This is very handy and efficient when reading protocol
+ * headers, e.g.
+ *   uint16_t sport = nptohs(&udp->th_sport);
+ * Note that it's ok to take the ADDRESS of members of unaligned structures,
+ * just never try to use the VALUE of the member.
+ */
+
+/* Convert the network order 32 bit integer pointed to by p to host order.
+ * p does not have to be aligned. */
+#define nptohl(p) \
+   ((((uint8_t*)(p))[0] << 24) | \
+    (((uint8_t*)(p))[1] << 16) | \
+    (((uint8_t*)(p))[2] << 8) | \
+    ((uint8_t*)(p))[3])
+
+/* Convert the network order 16 bit integer pointed to by p to host order.
+ * p does not have to be aligned. */
+#define nptohs(p) \
+   ((((uint8_t*)(p))[0] << 8) | ((uint8_t*)(p))[1])
+
+/* Copy the host order 16 bit integer in x into the memory pointed to by p
+ * in network order.  p does not have to be aligned. */
+#define htonps(p, x) \
+    do { \
+        ((uint8_t*)(p))[0] = (x & 0xFF00) >> 8; \
+        ((uint8_t*)(p))[1] = (x & 0x00FF) >> 0; \
+    } while (0)
+
+/* Copy the host order 32 bit integer in x into the memory pointed to by p
+ * in network order.  p does not have to be aligned. */
+#define htonpl(p, x) \
+    do { \
+        ((uint8_t*)(p))[0] = (x & 0xFF000000) >> 24; \
+        ((uint8_t*)(p))[1] = (x & 0x00FF0000) >> 16; \
+        ((uint8_t*)(p))[2] = (x & 0x0000FF00) >> 8; \
+        ((uint8_t*)(p))[3] = (x & 0x000000FF) >> 0; \
+    } while (0)
+
+#endif /* BYTEORDER_H */