setjmp: read the manual

[Dick Dunn]

Regarding the setjmp/longjmp interaction with register variables...
dmr gave one approach and justified it on the basis of "correct" behavior.
A response...
> There's a good reason for doing it the other way: efficiency...

Did I really miss something, or did someone just tell us that it is
reasonable to compromise correctness for efficiency?  I have a tough time
with such compromises.

>...
> We looked hard at this and decided to change the meaning of
> setjmp/longjmp (to the above) rather than having EVERY function save...

The parent article goes on to describe problems with saving all the
registers on a 68000.  In fact, there is a "whizzo" (his words) instruction
on the 68000 to save whatever set of registers you need, and you clearly
won't need to save all of them.

>...
> To fix a program that this breaks, you remove "register" declarations from
> routines that call setjmp.  Not so bad.

Actually, the task of fixing a program that breaks is a little harder:
First you have to realize that the problem is a setjmp/register
interaction.  Realistically, that might take days to find (particularly
if you're porting someone else's code).  I can't call that "not so bad".
-- 
Dick Dunn	{hao,ucbvax,allegra}!nbires!rcd		(303)444-5710 x3086
   ...Lately it occurs to me what a long, strange trip it's been.