David,
p.s. I think this power of two business is a bit over-hyped. The correct machine word size is and always has been 24 bits.
24? 24???!!! What kind of number is that?!? You can't even fit an entire file name into it (sixbit uppercase ASCII, naturally)!
Noooo.... You need 36 bits, my man. Split down the middle for those ordinary everyday tasks where 18 bit halfwords will do just fine, and in only half the resources too.
A PDP-10 with a KL10 core driving 40 Newbury terminals. That's what Squeak really needs!
(Seriously: AFAIK DEC never finished the design and implementation of the PDP-2 which would have added a 24-bit machine to the most elegant range of CPUs ever designed, IMO. That left either a few 24-bit offerings from Honeywell and the like, or move up to glorious 36-bit PDP-/DECsystem-10s.)
There are places with #flag: Dan lying around and Dan has expressed a lack of time to do anything with them but a willingness to sit with someone and a beer to explain what he was thinking of. I'm not going to be heading down to silicon valley anytime soon so I certainly can't do that but anyone that can take notes could do it and report back. Volunteers?
I could maybe do that next week. But here's what I remember as the last thoughts on the matter:
Plugins: This is mostly going to be tidying up declarations making sure int means machine width, foo * means machine pointer, sqOop means Squeak width pointer and sqInt means integer with same width as sqOop. Gratuitous casts between pointer and int all have to be replaced with appropriate macros/inline functions. (In fact I think all declarations should honestly and truthfully declare precisely the type of their value, including function pointers, with _no_ exceptions. While we're at it, functions returning nothing should be 'void', not 'int'.) Beyond that is hunting down and repairing 32-bit assumptions: divide/multiply by 4, shift by 2, mask by [~]3, etc. LargeIntegerPlugin might have some unique surprises waiting there. The parts of BitBlt and B3D that were never tested (NOTE: these plugins are NOT entirely converted yet) should be tested and repaired where needed. In some cases it's necessary to truncate to 32 bits to avoid unwanted carry out of 32 bits or to force sign extension out of bit 31. IIRC, graphics code had a few very hard to find issues along those lines. This is mostly mindless tedium with the occasional need to think seriously about the right type to use, made even more tedious by having to regenerate the plugin from the image ever few minutes having correlated a C line number with a statement in a Squeak method somewhere.
Taking advantage of 64-bit 'long's: We also discussed the two other obvious changes: SmallIntegers being represented as 63-bits + tag in 64-bit images, and 64-bit Bitmaps storing two 32-bit pixels in each word -- with a couple of additional primitives for 64-bit accesses. It could be the case that many of the 'flag:'s in the image are related to those two issues. Both of these go deep, and profoundly affect things both in the Interpreter and in various plugins. Not to be undertaken lightly.
I know Dan also wanted to clean up the base and method headers, in particular the split fields, in an incompatible image format change. Some 'flag:'s might be attached to those too.
If there was anything else then I'm afraid I can't remember it offhand now.
I think I remember Andreas working on the win32 support code to make it 64-bit clean(er), but I'm not certain.
Frankly I think we'd be making huge progress if we can just get the rest of the plugins to compile and run in both 64- and 32-bits, with sufficient confidence in their correctness to fold them back into the trunk.
I'd be more than happy to set up a repository for 64-bit support code while it's unstable. I could also, in case of dire need, offer accounts on 64-bit hardware for anyone who is eager to work on a particular plugin but has no 64-bit hardware to test their changes.
FWIW: one carrot to dangle in front of people as a motivator is that this work is only half concerned with running 64-bit images. The other half is about running 32-bit images on 64-bit hardware, which more and more people are finding to be a frustrating limitation.
Cheers, Ian