lwip/def.h: Simplify network byte order functions

[jjsuwa]

GCC built-in byte order functions

• __builtin_bswap16()
• __builtin_bswap32()
• __builtin_bswap64()

are just like as:

#define ALWAYS_INLINE static __inline__ __attribute__((always_inline))

/* merely example, sub-optimal implementation */
uint32_t ALWAYS_INLINE __inlined_bswapsi2(uint32_t u) {
    return ((u & 0xFF000000) >> 24)
         | ((u & 0x00FF0000) >>  8)
         | ((u & 0x0000FF00) <<  8)
         | ((u & 0x000000FF) << 24);
}
uint64_t ALWAYS_INLINE __inlined_bswapdi2(uint64_t u) {
    return ((u & 0xFF00000000000000ULL) >> 56)
         | ((u & 0x00FF000000000000ULL) >> 40)
         | ((u & 0x0000FF0000000000ULL) >> 24)
         | ((u & 0x000000FF00000000ULL) >>  8)
         | ((u & 0x00000000FF000000ULL) <<  8)
         | ((u & 0x0000000000FF0000ULL) << 24)
         | ((u & 0x000000000000FF00ULL) << 40)
         | ((u & 0x00000000000000FFULL) << 56);
}

/* seems to be as below */
uint16_t ALWAYS_INLINE __builtin_bswap16(uint16_t x) {
    return (x >> 8) | (x << 8);
}
uint32_t ALWAYS_INLINE __builtin_bswap32(uint32_t x) {
    extern uint32_t bswapsi2(uint32_t x);
    return __builtin_constant_p(x) ? __inlined_bswapsi2(x) : bswapsi2(x);
}
uint64_t ALWAYS_INLINE __builtin_bswap64(uint64_t x) {
    extern uint64_t bswapdi2(uint64_t x);
    return __builtin_constant_p(x) ? __inlined_bswapdi2(x) : bswapdi2(x);
}

/* placed to libgcc2.c */
uint32_t __attribute__((noinline)) bswapsi2(uint32_t u) {
    return __inlined_bswapsi2(u);
}
uint64_t __attribute__((noinline)) bswapdi2(uint64_t u) {
    return __inlined_bswapdi2(u);
}

[d-a-v]

Nice proposal but not in the right place, this is an official lwIP file.
It would have to be in arch/cc.h (by #define lwip_htons ...).
but even this one is not the right one because they are both overwritten by lwip2 installer.

Real source is in lwip2 repo.
A PR would make sense there.

[jjsuwa]

closed.