About JEP 338: Vector API

Thu Feb 11 10:23:11 UTC 2021

hi Remi,

this lib VectorHandler is a friendly  aproach of vector. 
Félicitation / good job

A little remarque : "Handler" is too generic.
        a better name would be "VectorCompute" , "VectorMath" 
"VectorMatrix" "Matrix" ....

Cordialement

Bruno LACOMBE

From:   forax at univ-mlv.fr
To:     "Paul Sandoz" <paul.sandoz at oracle.com>
Cc:     "b lacombe" <b.lacombe at lug.com>, "panama-dev at openjdk.java.net'" 
<panama-dev at openjdk.java.net>
Date:   10/02/2021 23:22
Subject:        Re: About JEP 338: Vector API

De: "Paul Sandoz" <paul.sandoz at oracle.com>
À: "Remi Forax" <forax at univ-mlv.fr>
Cc: "b lacombe" <b.lacombe at lug.com>, "panama-dev at openjdk.java.net'" 
<panama-dev at openjdk.java.net>
Envoyé: Mercredi 10 Février 2021 19:11:47
Objet: Re: About JEP 338: Vector API
Hi Remi, 

Thanks for pointing out it can be done using serialization, and people do 
that, since that is what's currently possible. I think it's problematic 
and we can do much better.

Paul.

It's not that awful :)
Enjoy https://github.com/forax/vector-handle

It should perform well but i've not done any perf tests.
And obviously, i've not implemented all the operations, only +, -, * and 
/, feel free to do some pull requests.

Rémi

On Feb 10, 2021, at 7:15 AM, Remi Forax <forax at univ-mlv.fr> wrote:

----- Mail original -----
De: "Paul Sandoz" <paul.sandoz at oracle.com>
À: "b lacombe" <b.lacombe at lug.com>
Cc: "panama-dev at openjdk.java.net'" <panama-dev at openjdk.java.net>
Envoyé: Mardi 9 Février 2021 00:10:57
Objet: Re: About JEP 338: Vector API

Hi Bruno,

You make a fair point about the complexity. The API is designed to be 
low-level
and literal, making use of current language features, requiring a vector
expression be built as an explicit tree (as if input to a compiler).

It would be interesting to express:

DoubleVector va = ...
DoubleVector vb = ...
DoubleVector vc = va.lanewise(vb, (double a, double b) -> -(a*b + b*b));

Whereby the Vector API can reflect over the scalar code of the lambda
expression. Then potentially use the same expression to operate over two
arrays, the implementation of which may utilize the same expression for 
fixed
length vectors over the variable length arrays.

It is a non-trivial exercise (an understatement!) to modify the Java 
language
and runtime in such a manner, but something like the above is what we have
mused about before, and I think is a promising approach.

Hi Paul,
you don't need to modify neither the language nor the JDK, using a 
serializable lambda should be enough.

A nice side effect of using hidden classes for the lambda proxies in jdk 
16 is that now the lambda proxy and the lambda itself are nestmate so if 
you have a Lookup from the class that contains the lambda, you can call 
writeReplace on the proxy which give you the SerializedLambda object which 
indicates the class and method name of the lambda once desugared. Once 
you've got that info, you can use ASM to extract the bytecode and do an 
abstract interpretation of the bytecode to create the corresponding 
expression tree. So still some work, but less than before.

Paul.

Rémi

On Feb 5, 2021, at 6:19 AM, b.lacombe at lug.com wrote:

About JEP 338: Vector API

A)  you write :
-----
static final VectorSpecies<Float> SPECIES = FloatVector.SPECIES_256;

void vectorComputation(float[] a, float[] b, float[] c) {

  for (int i = 0; i < a.length; i += SPECIES.length()) {
      var m = SPECIES.indexInRange(i, a.length);
  // FloatVector va, vb, vc;
      var va = FloatVector.fromArray(SPECIES, a, i, m);
      var vb = FloatVector.fromArray(SPECIES, b, i, m);
      var vc = va.mul(va).
                  add(vb.mul(vb)).
                  neg();
      vc.intoArray(c, i, m);
  }
}
-----
It is very complexe source code to write a simple (a*a+b )*-1

It 'll more easy, if we can write :
      FloatVector.forAll(a).mul(a).add(b).neg().toArray(c)
Where each operator (mul,add,neg) can make the convertion :
      var va=>FloatVector.fromArray(SPECIES, a, i, m) ...
Of course optimisation can be done  with a code like :
----
      void mul(a, ... buf){
              var va = cache.get(a);
              if( va==nul ){
                      va =  FloatVector.fromArray(SPECIES, a, i, m);
                      cache.put(a,va);
              }
              //here va
              .....
      }
----

2) A another optimisation can be make by preparing data  whith a "width"
operator like :
      FloatVector
              .width(a,b,c)
              .forAll(a)
              .mul(a).add(b).neg()
              .toArray(c);
then source is more easy to read, and less complex
what did you think ?

3) And if we can upgrade java grammar, a code like this for matrix :
              c = FloatVector[[ a*a+b*-1 ]]
would be ecxellent (where a,b,c must be final array) and so easy ....

Cordialement

Bruno LACOMBE
Multimédia SOLUTIONS
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