In addition to what Gregory has said, I think you need to use 0x80000000 rather than 0xffffffff in the expression.

x = 2^32 + 2^31
y = 2^32 + 2^31
? x      && 6442450944

* this will give a result of 2147483648
? BITAND(INT(x/0xffffffff),INT(y/0xffffffff))*0xffffffff;
+ BITAND(MOD(x,0xffffffff),MOD(x,0xffffffff))

* this gives 6442450944
? BITAND(INT(x/0x80000000),INT(y/0x80000000))*0x80000000;
+ BITAND(MOD(x,0x80000000),MOD(x,0x80000000))