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Some improvements in ntoh and hton macro


From: bastien
Subject: Some improvements in ntoh and hton macro
Date: Sun, 20 Oct 2002 15:25:44 +0200

Where I write network code I think they are a lack about a ntoh function on 
the 64 bits integers.
Moreover I think a type generic ntoh and  hton macro (like type generic math 
in tgmath.h ) is useful.

I implement this like :

/*begin code */
/* type generic bswap */
#define __bswap(x)\
( __extension__ (\
                {\
                __typeof__(x) __result=x;\
                switch(sizeof(x))\
                        {\
                        case 1:__result=x;break;\
                        case 2:__result=__bswap_16(x);break;\
                        case 4:__result=__bswap_32(x);break;\
                        case 8:__result=__bswap_64(x);break;\
                        }\
                __result;\
                }))

/* We can optimize calls to the conversion functions.  Either nothing has to 
be
done or we are using directly the byte-swapping functions which often can be
 inlined.  */
# if __BYTE_ORDER == __BIG_ENDIAN
/* The host byte order is the same as network byte order, so these functions
   are all just identity.  */
# define ntohl(x)       (x)
# define ntohs(x)       (x)
# define htonl(x)       (x)
# define htons(x)       (x)
/* my improvement */
# define htonll(x)      (x)
# define ntohll(x)      (x)
# define ntoh(x)        (x)
# define hton(x)        (x)
/* end */
# else
#  if __BYTE_ORDER == __LITTLE_ENDIAN
#   define ntohl(x)     __bswap_32 (x)
#   define ntohs(x)     __bswap_16 (x)
#   define htonl(x)     __bswap_32 (x)
#   define htons(x)     __bswap_16 (x)
/*my improvement */
#   define htonll(x)    __bswap_64 (x)
#   define ntohll(x)    __bswap_64 (x)
#   define ntoh(x)      __bswap (x)
#   define hton(x)      __bswap (x)
/*end */
#  endif
# endif
/* end code */

Gcc optimize very well this with the O flag but I think It is a good idea to 
define this only in _GNU_SOURCE scope

I hope a positive answer


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