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https://issues.apache.org/jira/browse/LUCENE-8533?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16655031#comment-16655031
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Uwe Schindler commented on LUCENE-8533:
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OK, I committed this change. IMHO, changing this is a larger task (it's not
only the -1 you mentioned). So I am closing this issue. If we want to change
this, we should open a new issue and plan the change.
> DataInput#readVInt() supports negative numbers although not documented
> ----------------------------------------------------------------------
>
> Key: LUCENE-8533
> URL: https://issues.apache.org/jira/browse/LUCENE-8533
> Project: Lucene - Core
> Issue Type: Improvement
> Reporter: Vladimir Dolzhenko
> Assignee: Uwe Schindler
> Priority: Major
> Attachments: LUCENE-8533_fix_readVInt_javadoc.patch, readVInt.patch
>
>
> {{readVInt()}} has to return positive numbers (and zero), throw some
> exception in case of negative numbers.
> While for the sequence of bytes {{[-1, -1, -1, -1, 15]}} it returns {{-1}}.
> simplifying
> [readVInt|https://github.com/apache/lucene-solr/blob/1d85cd783863f75cea133fb9c452302214165a4d/lucene/core/src/java/org/apache/lucene/store/DataInput.java#L113]
> up to last readByte (exclusive):
> {code:java}
> int i = ((byte)-1) & 0x7F;
> i |= (((byte)-1) & 0x7F) << 7;
> i |= (((byte)-1) & 0x7F) << 14;
> i |= (((byte)-1) & 0x7F) << 21;
> {code}
> Here {{i = 268435455}} or in binary format is
> {{00001111_11111111_11111111_11111111}}
> Keeping in mind that {{int}} is a signed type we have only 3 more bits before
> overflow happens or in another words {{(Integer.MAX_VALUE - i) >> 28 == 7}} -
> that's max value could be stored in 5th byte to avoid overflow.
> Instead of
> {code:java}
> i |= (b & 0x0F) << 28;
> if ((b & 0xF0) == 0) return i;
> {code}
> has to be
> {code:java}
> i |= (b & 0x07) << 28;
> if ((b & 0xF8) == 0) return i;
> {code}
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