DOS ain't dead

> As far as I know does the C standard has a few rules about aliassing. An
> alias is e.g. if you have two pointers of different types, then C assumes
> that they can't point to the same memory. (IOW one can't be an alias of
> the other)

That's also in the docs.

> A compiler can use that to optimize and reorder statements and
> assignments.
> -fno-strict-aliasing turns of that optimization, IOW their code is dirty
> and not ANSI C compatible.

But why is, e.g., Zlib faster then, if -fno-strict-aliasing turns off that optimization?

> So it turns off a valid optimization. It is afaik a typical optimization
> that is turned globally off if "strange" things happen.

I see.

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Forum admin

> As far as I know does the C standard has a few rules about aliassing. An
> alias is e.g. if you have two pointers of different types, then C assumes
> that they can't point to the same memory.

Did you mean something like this?

unsigned long *p1;
unsigned char p2[4]={1,2,3,4};

p1=(unsigned long *)p2;

Is p1 alias of p2? What's wrong on this code? Will it fails to compile if -fno-strict-aliasing enabled? U use such things of retyping very often, eg. when you have a char buffer and you want to access it as a structure.

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DOS gives me freedom to unlimited HW access.

> Today I found this article by Mike Acton of CellPerformance:
> Understanding
> Strict Aliasing

Thanks, interesting article and also more from this author.

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DOS gives me freedom to unlimited HW access.