Species-agnostic shuffle

[Vladimir Ivanov]

Hi Martin,

What about loading indices as a Vector first (using 
IntVector.fromArray()) and then converting it to VectorShuffle using 
Vector.toShuffle()?

Best regards,
Vladimir Ivanov

On 7/9/24 09:59, Martin Traverso wrote:
> Hi,
> 
> I've been experimenting with the Vector API in an attempt to port the 
> XXH3 hashing algorithm to Java. One of the steps requires rearranging 
> the elements of a vector by swapping adjacent values. I.e., (v0, v1, v2, 
> v3, ...) -> (v1, v0, v3, v2, ...).
> 
> One usability issue I'm running into is creating the VectorShuffle in a 
> species-agnostic manner. The VectorShuffle.fromArray() expects a number 
> of indices that matches *exactly* the length of the vector for the given 
> species, so it's harder to create a shuffle that uses SPECIES_PREFERRED 
> without additional logic to construct that array of indices dynamically.
> 
> To illustrate, I need to do the following for each species:
> 
>      VectorShuffle.fromArray(LongVector.SPECIES_128, new int[] { 1, 0 }, 0)
>      VectorShuffle.fromArray(LongVector.SPECIES_256, new int[] { 1, 0, 
> 3, 2 }, 0)
>      VectorShuffle.fromArray(LongVector.SPECIES_512, new int[] { 1, 0, 
> 3, 2, 5, 4, 7, 6 }, 0)
> 
> Of course, I could make something like this
> 
>      VectorShuffle.fromArray(LongVector.SPECIES_PREFERRED, 
> makeIndexesFromTemplate(new int[] { 1, 0 }), 0)
> 
> with my own custom "makeIndexesFromTemplate" function to create the 
> array of indices of the appropriate length.
> 
> Is there anything like that in the Vector APIs that I haven't been able 
> to find? If not, would it make sense to add something like it, or allow 
> VectorShuffle.fromXXX to derive such mapping?
> 
> - Martin
>