Re: [XenPPC] [pushed] [ppc] FPSCR and XER are really 64 bit quantities

[Jimi Xenidis <jimix@xxxxxxxxxxxxxx>]

On Apr 25, 2006, at 5:24 PM, Hollis Blanchard wrote:

> On Tue, 2006-04-25 at 16:54 -0400, Jimi Xenidis wrote:
> > On Apr 25, 2006, at 4:08 PM, Hollis Blanchard wrote:
> >
> > it is explained in the rest of the comment:
> >    - FPSCR should be save/restored with stfd/lfd since the 32 bit  
> > form
> >      can mangle the value.
> I read that; I still don't get it. If FPSCR is 32 bits, as all  
> available
> documentation claims, then couldn't you use stfiwx?
Yes, the FPSCR _is_ 32bits (I never claimed it was not) however the  
only way to store it is thru an FPR which is 64 bits.
We used to use lwfs/stfs but they convert from single to double  
respectively doing who-knows-what to the actual value.
It is possible to use stfiwx but there is no "load form" to match it  
(that I could see) and we would have to perform a full lfd for the  
restore thereby "forcing" us to use a 64bit quantity.  So I chose stf  
and ldf purely for symmetry.
> Your comment, on the other hand, claims it is 64 bits, and if that's
> true then you wouldn't use stfiwx. However, in that case, I'd like to
> know why you think it's 64 bits.
I used the word "quantities" to refer to storage rather that the  
register itself.
[ Actually, I'm just being a a smart-ass there :-) ]

-JX

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