Add fallback function for endian(3) family functions in isc/endian.h

Write simple bswap{16,32,64} macros and use them in place where
byteorder(3) functions are not appropriate (e.g. bigendian platforms
and 64-bit functions).

lib/isc/include/isc/endian.h

@@ -79,6 +79,68 @@
 
 #else
 
-#error Platform not supported
+#include <inttypes.h>
+
+#ifndef bswap16
+#define bswap16(x) ((uint16_t)((((uint16_t) (x) & 0xff00) >> 8) |	\
+			       (((uint16_t) (x) & 0x00ff) << 8)))
+#endif /* bswap16 */
+
+#ifndef bswap32
+#define bswap32(x) ((uint32_t)((((uint32_t) (x) & 0xff000000) >> 24) |	\
+			       (((uint32_t) (x) & 0x00ff0000) >> 8)  |	\
+			       (((uint32_t) (x) & 0x0000ff00) << 8)  |	\
+			       (((uint32_t) (x) & 0x000000ff) << 24)))
+#endif /* bswap32 */
+
+#ifndef bswap64
+#define bswap64(x) \
+	((uint64_t)((((uint64_t) (x) & 0xff00000000000000ull) >> 56) |	\
+		    (((uint64_t) (x) & 0x00ff000000000000ull) >> 40) |	\
+		    (((uint64_t) (x) & 0x0000ff0000000000ull) >> 24) |	\
+		    (((uint64_t) (x) & 0x000000ff00000000ull) >> 8)  |	\
+		    (((uint64_t) (x) & 0x00000000ff000000ull) << 8)  |	\
+		    (((uint64_t) (x) & 0x0000000000ff0000ull) << 24) |	\
+		    (((uint64_t) (x) & 0x000000000000ff00ull) << 40) |	\
+		    (((uint64_t) (x) & 0x00000000000000ffull) << 56)))
+#endif /* bswap64 */
+
+#if WORDS_BIGENDIAN
+
+#define htobe16(x) (x)
+#define htole16(x) bswap16(x)
+#define be16toh(x) (x)
+#define le16toh(x) bswap16(x)
+
+#define htobe32(x) (x)
+#define htole32(x) bswap32(x)
+#define be32toh(x) (x)
+#define le32toh(x) bswap32(x)
+
+#define htobe64(x) (x)
+#define htole64(x) bswap64(x)
+#define be64toh(x) (x)
+#define le64toh(x) bswap64(x)
+
+#else /* WORDS_BIGENDIAN */
+
+#include <arpa/inet.h>
+
+#define htobe16(x) htons(x)
+#define htole16(x) (x)
+#define be16toh(x) ntohs(x)
+#define le16toh(x) (x)
+
+#define htobe32(x) htonl(x)
+#define htole32(x) (x)
+#define be32toh(x) ntohl(x)
+#define le32toh(x) (x)
+
+#define htobe64(x) bswap64(x)
+#define htole64(x) (x)
+#define be64toh(x) bswap64(x)
+#define le64toh(x) (x)
+
+#endif /* WORDS_BIGENDIAN */
 
 #endif