Re: Keeping other stuff with addresses

On 12/3/2024 11:22 AM, MitchAlsup1 wrote:

On Tue, 3 Dec 2024 18:19:51 +0000, John Levine wrote:
 

According to Stefan Monnier  <monnier@iro.umontreal.ca>:

another way to steal bits is over alignment.

>
Yup.  I keep lamenting that Alpha didn't go for bit-addressed memory,
which would have given us 3 extra free bits from alignment (as well as
allowing pointers to bits and bitfields).

>
I thought STRETCH persuaded people that bit addressable memory was a bad
idea.

 With the address space STRETCH had bit addressability IS a VERY bad
Idea.
 We now have people (again) using the top bits of pointers for "special
things".
 Thus the Ferris wheel of invention is caught in a loop.

Stealing bit's wrt say, lock-free algorithms is usually about stealing from a pointer "value". think about C++'s std::uintptr_t, for a moment... Iirc, it may be optional, well, stealing bits from a pointer _value_ is non portable in and of itself. Although, they can be very useful, indeed... :^)