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<p>Hi Chris,<br>
this is a good question. The main reason as to why the check is
there is this: the code this new segment-based method replaces is
code that used to accept a ByteBuffer. The check you see there was
added just to make sure we didn't run into new and unexpected
situations.</p>
<p>Moving forward I could see this relaxed, either by tweaking the
API to accept an explicit layout from the user (so that the API
can check if the user really wants unaligned floats). Or, by doing
a different check which validates the maximum supported alignment
against the vector species. E.g. I suppose loading an int[] into a
DoubleVector is not ok - but float[]/int[]/short[]/char[]/byte[]
in FloatVector should be ok. But, going down that path is messy:
while heap segments keep track of their underlying Java array,
which can then be used to perform validation, an off-heap segment
doesn't have any particular alignment constraint. So (I think)
we're back to the user providing a layout parameter to the load
method.<br>
</p>
<p>Maurizio<br>
</p>
<p><br>
</p>
<p><br>
</p>
<p><br>
</p>
<p><br>
</p>
<div class="moz-cite-prefix">On 23/10/2023 12:10, Chris Hegarty
wrote:<br>
</div>
<blockquote type="cite" cite="mid:c2238394-bd23-4d7b-abcd-e3eb1568eaee@gmail.com">
<p>Hi,</p>
<p>I'm curious about the restriction when loading from heap backed
memory segments. E.g.<br>
</p>
<div style="background-color:#1e1f22;color:#bcbec4">
<pre style="font-family:'JetBrains Mono',monospace;font-size:9.8pt;"> <span style="color:#5f826b;font-style:italic;"> * </span><span style="color:#67a37c;font-style:italic;">@throws </span><span style="color:#5f826b;font-style:italic;">IllegalArgumentException if the memory segment is a heap segment that is
</span><span style="color:#5f826b;font-style:italic;"> * not backed by a {</span><span style="color:#67a37c;font-style:italic;">@code </span><span style="color:#5f826b;font-style:italic;">byte[]} array.
</span><span style="color:#5f826b;font-style:italic;"> * </span><span style="color:#67a37c;font-style:italic;">...</span><span style="color:#cf8e6d;">
</span> FloatVector <span style="color:#56a8f5;">fromMemorySegment</span>(VectorSpecies<Float> species, MemorgSegment ms, ...)</pre>
</div>
<p>Which results in:<br>
</p>
<p>jshell> float[] arr = new float[] { 1, 2, 3, 4, 5, 6, 7, 8 }<br>
arr ==> float[8] { 1.0, 2.0, 3.0, 4.0, 5.0, 6.0, 7.0, 8.0 }<br>
<br>
jshell> var vec =
FloatVector.fromMemorySegment(FloatVector.SPECIES_PREFERRED,
MemorySegment.ofArray(arr), 0, ByteOrder.nativeOrder())<br>
| Exception java.lang.IllegalArgumentException<br>
| at ScopedMemoryAccess.loadFromMemorySegment
(ScopedMemoryAccess.java:334)<br>
| at FloatVector.fromMemorySegment0Template
(FloatVector.java:3353)<br>
| at Float128Vector.fromMemorySegment0
(Float128Vector.java:864)<br>
| at FloatVector.fromMemorySegment
(FloatVector.java:2986)<br>
| at do_it$Aux (#43:1)<br>
| at (#43:1)<br>
<br>
</p>
<p>I can see that this is deliberate ...</p>
<div style="background-color:#1e1f22;color:#bcbec4">
<pre style="font-family:'JetBrains Mono',monospace;font-size:9.8pt;"><span style="color:#16baac;"> V </span><span style="color:#56a8f5;">loadFromMemorySegmentMasked</span>(...) {
<span style="color:#7a7e85;">// @@@ Smarter alignment checking if accessing heap segment backing non-byte[] array
</span><span style="color:#7a7e85;"> </span><span style="color:#cf8e6d;">if </span>(msp.maxAlignMask() > <span style="color:#2aacb8;">1</span>) {
<span style="color:#cf8e6d;">throw new </span>IllegalArgumentException();
}</pre>
</div>
<p>Is this just temporary? I would expect the alignment to be as
if `<font face="monospace">ValueLayout.JAVA_FLOAT.withByteAlignment(1)</font>`,
no? Is the intent to eventually support other non-byte primitive
array typed, and to require and check alignment? It should just
work, right?</p>
<p>--<br>
</p>
<p>The reason I ask about this is that over in Luceneland we're
considering a switch to loading vector data from float[] to
MemorySegment - which allows to load search vectors directly
from the mmapped index file. But we still have some code paths
which have float[], which may or may not be coming from the
mmapped file. So we end up with something like this:</p>
<p><font face="monospace"> dotProduct(float[] a, float[] b)</font></p>
<p><font face="monospace"> dotProduct(float[] a, MemorySegment b)</font></p>
<p><font face="monospace"> dotProduct(</font><font face="monospace">MemorySegment</font><font face="monospace">
a, MemorySegment b)</font></p>
<p>... and we have cosine and Euclidean distance too. We can of
course write the three variants of the code (and we've done
this), just that it would be desirable to have the float[]
accepting methods just wrap and delegate to the MemorySegment
variant. In our use case, we don't slice or offset into the heap
segment, but I do see how things could get misaligned quite
quickly, but again I expect this to behave as if with byte
alignment(1).<br>
</p>
<p>Thanks,</p>
<p>-Chris.<br>
</p>
</blockquote>
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