typedef __u32 __bitwise __be32 means in linux [duplicate]

I extract from file (http://cpansearch.perl.org/src/HAWK/IPTables-libiptc-0.52/include/linux/types.h ) these defines :

#ifdef __CHECKER__
#define __bitwise__ __attribute__((bitwise))
#else
#define __bitwise__
#endif
#ifdef __CHECK_ENDIAN__
#define __bitwise __bitwise__
#else
#define __bitwise
#endif

typedef __u16 __bitwise __le16;
typedef __u16 __bitwise __be16;
typedef __u32 __bitwise __le32;
typedef __u32 __bitwise __be32;
#if defined(__GNUC__)
typedef __u64 __bitwise __le64;
typedef __u64 __bitwise __be64;
#endif
typedef __u16 __bitwise __sum16;
typedef __u32 __bitwise __wsum;

what does #define bitwise _attribute_((bitwise)) mean?

and what does typedef __u32 __bitwise __be32; mean?

原文地址:http://stackoverflow.com/questions/17473151/typedef-u32-bitwise-be32-means-in-linux