[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
Re: [f-cpu] Re: Floating-Point?
On Thu, Aug 16, 2001 at 01:49:27PM +0800, Glenn Alexander wrote:
> Hi. This is my first post to this list. My background is as a hardware
> technician, not a chip designer so bear with me.
>
> On Thursday 16 August 2001 03:41, you wrote:
> > Michael Riepe a écrit :
> >
> > In sparc, there is no 80 bits float but 128 bits (2 registers used in
> > the same time). We don't need 1 cycle multiplication so it could be done
> > for the fcpu.
>
> I am thinking that taking the two-register approach might be
> over-complicating matters. Since F-CPU is intended to later be scaled above
> 64 bits, if someone wanted 128-bit floats in the future they would impliment
> a 128-bit F-CPU. Especially for the FC-0 and probably for the FC-1, KISS
> (Keep It Simple for us Stupid people).
128-bit `quadruple precision' (like SPARC) is IMHO the way to go, but
not in the FC0. For now, let's stick to 32-bit and 64-bit (with 80-bit
`double extended' used inside the FP unit, to maintain IEEE compliance).
> BTW: I am wondering about the reasons for having endian-ness encoded in the
> instruction. How often do you need to change endinianness. I am thinking a SR
> for endinian would free up that bit as well as allowing other endiniannesses
> as well as big and little (Not in popular usage at present but I can think of
> several other bizaar ways to re-arrange the bits in a word that may be useful
> in some obscure application).
Please don't. Mode registers are a PITA. You never know whether
they're set correctly (like the `D' flag on x86). Except for the
register width translation SRs, NO special register should affect
the semantics of a program!
We could drop the `e' flag and use [s]byterev.* to swap the bytes.
But byterev takes 3 extra cycles to execute, while load/store don't slow
down in `foreign-endian' mode.
--
Michael "Tired" Riepe <Michael.Riepe@stud.uni-hannover.de>
"All I wanna do is have a little fun before I die"
*************************************************************
To unsubscribe, send an e-mail to majordomo@seul.org with
unsubscribe f-cpu in the body. http://f-cpu.seul.org/