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https://issues.apache.org/jira/browse/LUCENE-1990?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12803872#action_12803872
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Toke Eskildsen commented on LUCENE-1990:
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I think Michaels generated code was meant as a temporary solution, until a
handcrafted version was available. In packed32 and packed64, the code for
decoding a value is
{code}
public long get(final int index) {
final long majorBitPos = index * elementBits;
final int elementPos = (int)(majorBitPos >>> BLOCK_BITS); // / BLOCK_SIZE
final int bitPos = (int)(majorBitPos & MOD_MASK); // % BLOCK_SIZE);
final int base = bitPos * FAC_BITPOS;
return ((blocks[elementPos] << shifts[base]) >>> shifts[base+1]) |
((blocks[elementPos+1] >>> shifts[base+2]) & readMasks[bitPos]);
}
{code}
which looks a lot like your (Paul Elschot) suggestion. It avoids all
conditionals at the cost of more bit-operations and a dummy element at the end
of the backing array. I must admit that my performance testing of the different
solutions has been fairly ad hoc (measure, tweak, repeat), so an appropriate
test would be in order.
> Add unsigned packed int impls in oal.util
> -----------------------------------------
>
> Key: LUCENE-1990
> URL: https://issues.apache.org/jira/browse/LUCENE-1990
> Project: Lucene - Java
> Issue Type: Improvement
> Components: Index
> Reporter: Michael McCandless
> Priority: Minor
> Attachments: LUCENE-1990-te20100122.patch, LUCENE-1990.patch,
> LUCENE-1990_PerformanceMeasurements20100104.zip
>
>
> There are various places in Lucene that could take advantage of an
> efficient packed unsigned int/long impl. EG the terms dict index in
> the standard codec in LUCENE-1458 could subsantially reduce it's RAM
> usage. FieldCache.StringIndex could as well. And I think "load into
> RAM" codecs like the one in TestExternalCodecs could use this too.
> I'm picturing something very basic like:
> {code}
> interface PackedUnsignedLongs {
> long get(long index);
> void set(long index, long value);
> }
> {code}
> Plus maybe an iterator for getting and maybe also for setting. If it
> helps, most of the usages of this inside Lucene will be "write once"
> so eg the set could make that an assumption/requirement.
> And a factory somewhere:
> {code}
> PackedUnsignedLongs create(int count, long maxValue);
> {code}
> I think we should simply autogen the code (we can start from the
> autogen code in LUCENE-1410), or, if there is an good existing impl
> that has a compatible license that'd be great.
> I don't have time near-term to do this... so if anyone has the itch,
> please jump!
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