htonl() vs __builtin_bswap32()

Question

__builtin_bswap32() is used to reverse bytes (it\'s used for littel/big endian issues (from gcc)).

htonl() is used to reverse bytes too (conver

Answer 1

Just look at source code : (example from glib 2.18)

#undef htonl
#undef ntohl

uint32_t
htonl (x)
uint32_t x;
{
    #if BYTE_ORDER == BIG_ENDIAN
       return x;
    #elif BYTE_ORDER == LITTLE_ENDIAN
       return __bswap_32 (x);
    #else
       # error "What kind of system is this?"
    #endif
}
weak_alias (htonl, ntohl)

And : #define __bswap_32(x) ((unsigned int)__builtin_bswap32(x))

Source here : http://fossies.org/dox/glibc-2.18/htonl_8c_source.html

As you can see, htonl only call __builtin_bswap32 on little-endian machines.