C++ reverse swap32

c++ common function
read integer
static U32 XXH_read32(const void* memPtr)
{ U32 val; memcpy(&val, memPtr, sizeof(val)); return val; }

static U32 XXH_read32(const void* memPtr)
{
U32 val;
memcpy(&val, memPtr, sizeof(val));
return val;
}

反序
static U32 XXH_swap32 (U32 x)
{
return ((x << 24) & 0xff000000 ) |
((x << 8) & 0x00ff0000 ) |
((x >> 8) & 0x0000ff00 ) |
((x >> 24) & 0x000000ff );
}
static U64 XXH_swap64 (U64 x)
{
return ((x << 56) & 0xff00000000000000ULL) |
((x << 40) & 0x00ff000000000000ULL) |
((x << 24) & 0x0000ff0000000000ULL) |
((x << 8) & 0x000000ff00000000ULL) |
((x >> 8) & 0x00000000ff000000ULL) |
((x >> 24) & 0x0000000000ff0000ULL) |
((x >> 40) & 0x000000000000ff00ULL) |
((x >> 56) & 0x00000000000000ffULL);
}

XXH_CPU_LITTLE_ENDIAN
#ifndef XXH_CPU_LITTLE_ENDIAN
static const int g_one = 1;
#define XXH_CPU_LITTLE_ENDIAN ((const char)(&g_one))
#endif