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Hi Paul,</div>
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Thank you for the detailed response.</div>
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I appreciate this does not appear to be an urgent issue at this stage, and that there is a plan to address it eventually.</div>
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As the current toLong/fromLong helpers make the non-scalable code the easy path, I'm concerned that only adding an overload without deprecating/removing the original methods might leave a space for the portability issue: any library using the original toLong/fromLong
would prevent applications from scaling to wider vector lengths.</div>
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I'd like to propose this similar option for consideration:</div>
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1. Introduce methods with the names emphasizing they deal with a part of mask only:</div>
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- long toLongChunk(int chunkIndex)</div>
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- static VectorMask<E> fromLongChunk(VectorSpecies<E> species, int chunkIndex, long bits)</div>
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- int longChunkCount()</div>
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2. Deprecate (and eventually remove, while in incubator stage) fromLong / toLong - to steer towards the scalable version.</div>
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Does this direction seem reasonable?</div>
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There are a couple of other ideas on potential alternative approaches:</div>
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1. Using `long[]` array returned by `toLong` and accepted by `fromLong`. Presumably, there is an issue with having to allocate object even for 1-2 `long` chunks.</div>
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2. If value types are considered for Vector API, using a `{ long, long, long, long }` value to represent the bitmask returned by `toLong` / accepted by `fromLong` methods. This, however, would still keep a certain limit to the vector width.</div>
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Separately, it might be helpful to have a diagnostic/testing portability-check mode of running a Java program that uses Vector API - which would provide the maximum vector size wider than supported by the hardware. This does not have to be optimized for performance,
as the goal would be to ensure/verify semantic correctness with wider vectors.</div>
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What do you think about this?</div>
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Kind regards,</div>
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Ruben</div>
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<div id="divRplyFwdMsg" dir="ltr"><font face="Calibri, sans-serif" style="font-size:11pt" color="#000000"><b>From:</b> Paul Sandoz <paul.sandoz@oracle.com><br>
<b>Sent:</b> 30 January 2026 23:20<br>
<b>To:</b> Ruben Ayrapetyan <Ruben.Ayrapetyan@arm.com><br>
<b>Cc:</b> panama-dev@openjdk.org <panama-dev@openjdk.org>; Paul Sandoz <psandoz@openjdk.org><br>
<b>Subject:</b> Re: Vector API support for vectors wider than 512 bits</font>
<div> </div>
</div>
<div style="line-break:after-white-space">Hi Ruben,
<div><br>
</div>
<div>They should be refined eventually, perhaps by adding an override accepting a part number following similar patterns in other places of the API. A reason why we have not prioritized this so far is: </div>
<div><br>
</div>
<div>1) AFAICT there is currently no commonly available hardware that goes beyond a cache line size in vector size. Thereby reducing the urgency. I would be interested in knowing if my assumption is incorrect!</div>
<div><br>
</div>
<div>2) There are related implementation issues when shuffling bytes, since the underlying shuffle implementation of bytes stores the indices in a byte[] array. This is more disruptive to address than the first one.</div>
<div> </div>
<div>Paul.<br id="x_lineBreakAtBeginningOfMessage">
<div><br>
<blockquote type="cite">
<div>On Jan 30, 2026, at 3:05 AM, Ruben Ayrapetyan <Ruben.Ayrapetyan@arm.com> wrote:</div>
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Hi all,</div>
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The question is related to Vector API compatibility with various vector lengths.</div>
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Some of the interfaces appear to be limiting support to 512-bit vectors, for example:</div>
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- VectorMask.toLong throws an exception for vectors with more than 64 lanes;</div>
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- VectorMask.fromLong replicates the sign bit into lane 64 and beyond.</div>
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As far as I understand from the documentation, the wider vectors are meant to be supported though not necessarily optimized for initially:</div>
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"Although the API has been designed to ensure ARM SVE instructions can be supported (vector sizes between 128 and 2048 bits)"</div>
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As the Java programs using the interfaces might not be compatible with an architecturally valid hardware platform, is there a possibility to refine the interfaces to ensure they scale to wider vectors?</div>
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Kind regards,</div>
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Ruben</div>
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</div>
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