Hi, I was curious if anyone could shed some light on the following question I've had. So if I understand this correctly the freelists use the upper 16bits of the data ptr to be a "version," where this version tries to solve several problems related to lockfree data structures including the ABA problem and the delete after remove problem. So in my quest to understand these more, I'm trying to figure why the macros are so complex, for example:
#define FREELIST_POINTER(_x) ((void*)(((((intptr_t)(_x).data)<<16)>>16) | \ (((~((((intptr_t)(_x).data)<<16>>63)-1))>>48)<<48))) Since the pointer is just the lower 48 bits, isn't it enough to just do something like: (void*)(((intptr_t)(_x).data) & (intptr_t)(0x0000FFFFFFFFFFFFULL))) It would seem like we should be able to pull this off with only a single machine instruction? Which is surprising that we dont when the freelist version macro is much simpler: #define FREELIST_VERSION(_x) (((intptr_t)(_x).data)>>48) I know some pretty smart people worked on this stuff so I'm sure there is a very good reason for the complexity, but I just cant figure it out. Anyone? Brian
