Re: How many vector registers are useful?

kirchner@uklira.informatik.uni-kl.de (Reinhard Kirchner) writes:
> A register has an optimizing effect only when the value in it can be used
> several times, ...


jlg@cochiti.lanl.gov (J. Giles) writes:
>[Another effect] (also true of scalars) is when the value is
>an intermediate.


Suppose one considers a not too outlandish problem, namely, that of
producing a vector of non-uniform random variables (exponential, normal,
gamma, beta, etc.). It is possible to vectorize the reasonably efficient
acceptance-rejection and acceptance-replacement methods available, at
least if there is a reasonable use of control vectors, and a typical such
procedure will use about a half-dozen registers. Many of these procedures
need division, and if division has to be stepped, it will add another
register or so.


If only one vector process can be done at a time, so far so good. But
many vector machines can parallelize the vector processes, so we have a
cause for proliferation. Even if only load and store can be parallelized
with vector computation, we can add a few more. So it would not surprise
me if a few dozen would not be a good idea.
--
Herman Rubin, Dept. of Statistics, Purdue Univ., West Lafayette IN47907-1399
Phone: (317)494-6054
hrubin@snap.stat.purdue.edu (Internet, bitnet)
{purdue,pur-ee}!snap.stat!hrubin(UUCP)
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