On Aug 14, 2012, at 2:09 AM, Vincent Habchi <vi...@macports.org> wrote:
> Le 13 août 2012, à 23:47, Mike Abdullah <cocoa...@mikeabdullah.net> scripsit: > >> An idea I've vaguely wondered about would be turning the isa variable into a >> tagged pointer. If you know nothing is accessing it directly (to do so was >> deprecated with the modern runtime), then, say, the last 4 bits of the >> pointer could be used to record the retain count. Once they're used up (for >> those rare, highly retained > > Using part of pointer to do something else than record an address is > perilous. I remember, once again in the old days of the 68000 on the Atari > ST, which had a 24-bit external address bus (and not 20 as I wrote before on > some other thread), and 32-bit internal address registers, some developers > had figured out to use the MSB (unused) of these address registers (pointers) > to store extra information. Now, two years later the 68020 with full 32-bit > external address bus was released, and suddenly all the code relying on that > trick broke on the TT and later machines… Same thing happened on the original 68k Macintosh. It was bad enough that for quite some time Apple actually had to leave a setting in the control panel to turn off 32-bit addressing, since it broke so much older software. Charles _______________________________________________ Cocoa-dev mailing list (Cocoa-dev@lists.apple.com) Please do not post admin requests or moderator comments to the list. Contact the moderators at cocoa-dev-admins(at)lists.apple.com Help/Unsubscribe/Update your Subscription: https://lists.apple.com/mailman/options/cocoa-dev/archive%40mail-archive.com This email sent to arch...@mail-archive.com
