Disregard this question, it's not doing what I originally expected it was doing based on the name.
Brian On Wed, Sep 5, 2012 at 8:45 PM, Brian Geffon <bri...@apache.org> wrote: > 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
