Re: [fpu] Rounding Again

[Jamil Khatib <jamilkhatib75@yahoo.com>]

--- Rudolf Usselmann <russelmann@hotmail.com> wrote:
> 
> >From: Damjan Lampret <damjanlampret@yahoo.com>
> >To: Rudolf Usselmann <russelmann@hotmail.com>
> >
> > > I'm still having a hard time with rounding.
> > >
> > > I did get the book you recommended. I still
> don't understand binary
> > > rounding. I understand the math, but can't see
> how the GRS bits are
> > > used. It's somehow confuses me. I have read a
> lot on this subject
> > > now,
> > > but can't believe that there is no step by step
> explanation ...
> >
> >I knew details but forgot (this was a year or so
> ago). Anyway I know
> >that this is used when you shift the result to
> right (if I remember)
> >and you compare shifted result with another shifter
> result that is
> >shifted for one bit more. And GRS bits are the one
> most right and tell
> >you whether you have precise number as it supposed
> to be after
> >normalizing or it is not precise. Anyway something
> like that. I am
> >trying to find pieces of this in my mind. ;-)
> >
> >I can take a look in Hennessy and Patterson book
> where FP is also
> >explained (I think there is much easier explained
> since their books are
> >targeted to students).
> 
> I have that book as well. I still don't get it.
> Here is what I got from all the books:
> 
> 1) You take the operands, increase the precision by
>    appending 3 zeros at the right. (So your
> fractions
>    are now 23+3=26 bits wide)
> 2) Preshift (Normalize).
> 3) Add
> 4) Normalize (count leading zeros and shift)
>    The shifted result shifted in to GRS, if shifted
> right
>    (where S is sticky), otherwise GRS are zero (and
> ignored).
> 

I can not get your point here, do you want to prepare
the value then perform the addition? or what do you do
in step 3.?

> Is this correct so far ???
> What do I do next ?
> 
> >regards,
> >Damjan
> 
> rudi
>
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