On Mon, 30 Mar 2026 17:24:42 GMT, Paul Sandoz <[email protected]> wrote:

>> Emanuel Peter has updated the pull request incrementally with one additional 
>> commit since the last revision:
>> 
>>   two changes for Paul
>
> We can either add documentation to package doc or to a separate HTML file in 
> the same package. But for this review I realize I am likely asking too much, 
> it would be better to consider that holistically.
> 
> I wonder if we can remove footnote-like text such as "(Some platforms do 
> support a..."? and perhaps it is possible after the definitions to 
> compress/remove most of the discussion before we focus on the various 
> resizing operations, maybe provide a textual example for each, and then on to 
> the table of the examples that amplifies with more examples?

@PaulSandoz Thanks for the online and offline comments!

> I wonder if we can remove footnote-like text such as "(Some platforms do 
> support a..."?

This was from @rose00 , so I have not yet dared to remove it. I think it also 
nicely explains the rationale behind part numbers. For example on NEON, we 
really currently can only use 64 and 128 bit vectors. That is a very narrow 
band, and makes casting less straight-forward: you need to think about 
inserting and selecting.

With synthetic vector shapes we can probably get around this. Even vector 
splitting could help: casting from 128 bit to 512 bit would then automatically 
split the 512 bit one into 4 vectors on NEON. At that point, we may need to 
re-write some of these sections.

@rose00 What is your opinion on this paragraph?

Quoting the whole thing for reference:

> (Some platforms do support a rich variety of vector shapes, and can also 
> natively express logical expansions and contractions of lanewise data, 
> transparently adjusting vector shapes on the fly. But not all platforms have 
> enough shapes to pull this off well. And in extreme cases a shape change is 
> physically impossible, because the logical result would be just too large or 
> too small to be matched by any available vector shape. So the Vector API only 
> changes shapes in a method documented as shape-changing, and the user must 
> supply the new shape explicitly.)

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PR Comment: https://git.openjdk.org/jdk/pull/30113#issuecomment-4160044385

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