A 17-bit lookup table for a 17x1024 sized Y would require 16 MB. The 4-bit
version is 10kb and would fit into the L1 cache. I believe the L1 vs RAM
access times are 1-to-60 or so (http://www.7-cpu.com/cpu/Haswell.html).

Of course, maybe we use few enough Xs at any given time that the relevant
entries of a 17-bit LUT would be hot anyway.

On Thu, Oct 13, 2016 at 8:04 PM, Raul Miller <rauldmil...@gmail.com> wrote:

> Simplest "high performance" version of that would be to pre-compute each of
> the possible answers for each possible X.
>
> --
> Raul
>
>
> On Thu, Oct 13, 2016 at 9:33 PM, Michal Dobrogost <
> michal.dobrog...@gmail.com> wrote:
>
> > Yes, you can rewrite (+./@:*.) as (+./ . *.).
> >
> > Hehe, in terms of peculiar ways and unknown reasons, I invite you to
> think
> > about how you might go about implementing a high-performance version of
> > this operation where X and Y are restricted to boolean elements, Y is
> > static and X dynamically changes.
> >
> > On Thu, Oct 13, 2016 at 10:32 AM, Erling Hellenäs <
> > erl...@erlinghellenas.se>
> > wrote:
> >
> > > It is this operation +./ . *. we rewrite in peculiar ways for unknown
> > > reasons?
> > >
> > > [ x=: 1 0 1 1 0
> > >
> > > 1 0 1 1 0
> > >
> > > [ y=: 5 6 $1 0 0 0 0 0 0 1 0 1 1 0 0 1 0 0 0 1 0 0 0 0 1 1 0 1 1 1 0 1
> > >
> > > 1 0 0 0 0 0
> > >
> > > 0 1 0 1 1 0
> > >
> > > 0 1 0 0 0 1
> > >
> > > 0 0 0 0 1 1
> > >
> > > 0 1 1 1 0 1
> > >
> > > x +./ . *. y
> > >
> > > 1 1 0 0 1 1
> > >
> > >
> > > /Erling
> > >
> > >
> > >
> > > ----------------------------------------------------------------------
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> > >
> > ----------------------------------------------------------------------
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> >
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