AVR byte swap optimization

[Eric Christopher]

On Nov 19, 2006, at 10:18 PM, Rask Ingemann Lambertsen wrote:

> On Sun, Nov 19, 2006 at 02:46:44PM -0800, Eric Christopher wrote:
>
>>> These two versions would rule on the i386 if GCC would be just a
>>> little bit smarter:
>>
>> I prefer the single instruction bswap that we now generate for
>> __builtin_bswap[32,64] myself...
>
>    But that's only available starting with the i486. We should still  
> produce
> good code for an i386. On the m68k, we also want something with three
> rotates, say
>

I suppose, not much is being shipped that doesn't have the i486  
instructions
these days.

> 	rol.w	$8, d0
> 	swap.l	d0
> 	rol.w	$8, d0
>

Well, there's a bswap opcode now...

-eric