Ciao,
Il 2019-11-19 22:20 ni...@lysator.liu.se ha scritto:
"Marco Bodrato" <bodr...@mail.dm.unipi.it> writes:
Il Mar, 19 Novembre 2019 7:50 pm, Torbjörn Granlund ha scritto:
If there is special code for several asl cases, doesn't that defeat
the
purpose of asl, at least to some extent?
I think it defeats small-limb testing of mini-gmp. If it makes mini-gmp
with small limbs much faster, it might aid small-limb tests of mpfr.
Not only, it also aid small-limb testing of the implementations in
mini-gmp of gcd, primality testing, combinatorics, modular
exponentiation...
It is possible (and not really difficult, I think) to adapt the
default
code and remove any special shortcut from both those functions too.
When the special code was added (about a year ago, 2018-12-21), was
that
as an optimization, or because the original code didn't work properly
for small limb size?
The special code for umul_ppmm was added for speed. The generic code
works also for smaller limbs.
On the invert_3by2 side, the same kind of optimisation was used. Not
only for speed, I have to admit, but also because the code could get
simpler.
I was thinking also to some embedded systems I used some years ago,
where "unsigned long" was supported by the compiler, but slow on the
hardware...
But currently also those embedded systems are probably obsolete.
I think that special code to use plain unsigned long multiplication
and
plain unsigned long division for those two critical macros, when limbs
are
small enough, is a reasonable compromise.
Maybe for umul_ppmm, but I disagree about mpn_invert_3by2. The latter
function isn't used in any inner loops.
Ok. We can decide to keep a single variant for mpn_invert_3by2.
Will changing the type currently used for "half limbs", taking care of
negations and carry detection... be enough? We should try.
Ĝis,
m
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