Re: 80286 protected mode

On Wed, 9 Oct 2024 20:22:16 +0000, David Brown wrote:

On 09/10/2024 20:10, Thomas Koenig wrote:

David Brown <david.brown@hesbynett.no> schrieb:
>

When would you ever /need/ to compare pointers to different objects?
For almost all C programmers, the answer is "never".

>
Sometimes, it is handy to encode certain conditions in pointers,
rather than having only a valid pointer or NULL.  A compiler,
for example, might want to store the fact that an error occurred
while parsing a subexpression as a special pointer constant.
>
Compilers often have the unfair advantage, though, that they can
rely on what application programmers cannot, their implementation
details.  (Some do not, such as f2c).

>
Standard library authors have the same superpowers, so that they can
implement an efficient memmove() even though a pure standard C
programmer cannot (other than by simply calling the standard library
memmove() function!).

This is more a symptom of bad ISA design/evolution than of libc
writers needing superpowers.