On Fri, 23 Nov 2007, Heikki Orsila wrote:
> On Fri, Nov 23, 2007 at 12:15:53AM +0000, Daniel Drake wrote:
> > Why unaligned access is bad
> > ===========================
> >
> > Most architectures are unable to perform unaligned memory accesses. Any
> > unaligned access causes a processor exception.
>
> "Some architectures are unable to perform unaligned memory accesses,
> either an exception is generated, or the data
> access is silently invalid. In architectures that allow unaligned
> access, natural aligned accesses are usually faster than non-aligned."
>
> > In summary: if your code causes unaligned memory accesses to happen, your code
> > will not work on some platforms, and will perform *very* badly on others.
>
> *very* -> *slower*
>
> > Natural alignment
> > =================
>
> Please move this definition before "Why unaligned access is bad".
>
> Also, it would be nice to have a table of ISAs:
>
> ISA Need Need
> natural alignment
> alignment by x
> --------------------------------------------
> m68k No 2
`No' for >= 68020.
`Yes' for < 68020.
> powerpc/ppc Yes Word size
> x86 No No
> x86_64 No No
Gr{oetje,eeting}s,
Geert
--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- [email protected]
In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
-- Linus Torvalds
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