Bit operation of extract flags into 24 bit integer

I saw a line in xen's kernel code (file: xen/include/asm-x86/x86_64/page.h), but cannot understand why they are doing this:

/* Extract flags into 24-bit integer, or turn 24-bit flags into a pte mask. */                                                                      
#define get_pte_flags(x) (((int)((x) >> 40) & ~0xFFF) | ((int)(x) & 0xFFF))                                                                         
#define put_pte_flags(x) (((intpte_t)((x) & ~0xFFF) << 40) | ((x) & 0xFFF))     

As to

#define get_pte_flags(x) (((int)((x) >> 40) & ~0xFFF) | ((int)(x) & 0xFFF)) 

I understand ((int)(x) & 0xFFF) will extract the last 24 bits of x, but why they need the first part ((int)((x) >> 40) & ~0xFFF) ?

As to

  #define put_pte_flags(x) (((intpte_t)((x) & ~0xFFF) << 40) | ((x) & 0xFFF))  

I'm lost at the purpose of ((intpte_t)((x) & ~0xFFF) << 40). It should be 0 in my opinion. Then why do we need it?

Thanks,