[libre-riscv-dev] [isa-dev] Re: Vector Operations Extension (cross, dot, length, lerp, slerp)

[Hendrik Boom]

On Sun, Oct 06, 2019 at 10:36:37PM -0700, Jacob Lifshay wrote:
> On Sat, Oct 5, 2019 at 2:39 AM lkcl <luke.leighton at gmail.com> wrote:
> >
> > http://bugs.libre-riscv.org/show_bug.cgi?id=142
> > (Tracking this extension here)
> >
> > Found a paper which describes vector normalisation in terms of dotproduct, scalar recipsqrt and then scalar-vector fmul.
> 
> Yeah, that's the standard procedure.
> 
> > With VLENGTH being also expressible as dotproduct followed by scalar sqrt, is it reasonable to have both normalisation as well as VLENGTH as macro op fused sequences?

Vector length would presumably involve dotting a vector with itself.  
The potential advantage I see is that the dot product might be tempted 
to read that vector twice; whereas the length would only read it once.
If some other mechanism eliminates the duplicate read, they would be 
pretty well equivalent.

-- hendrik
> 
> I would think so, though I can't say for sure.
> 
> Jacob
> 
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