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https://issues.apache.org/jira/browse/LUCENE-1606?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12781746#action_12781746
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Robert Muir commented on LUCENE-1606:
-------------------------------------
Yonik, maybe we can use this trick?
UTF-8 in UTF-16 Order
The following comparison function for UTF-8 yields the same results as UTF-16
binary
comparison. In the code, notice that it is necessary to do extra work only once
per string,
not once per byte. That work can consist of simply remapping through a small
array; there
are no extra conditional branches that could slow down the processing.
{code}
int strcmp8like16(unsigned char* a, unsigned char* b) {
while (true) {
int ac = *a++;
int bc = *b++;
if (ac != bc) return rotate[ac] - rotate[bc];
if (ac == 0) return 0;
}
}
static char rotate[256] =
{0x00, ..., 0x0F,
0x10, ..., 0x1F,
. .
. .
. .
0xD0, ..., 0xDF,
0xE0, ..., 0xED, 0xF0, 0xF1,
0xF2, 0xF3, 0xF4, 0xEE, 0xEF, 0xF5, ..., 0xFF};
{code}
The rotate array is formed by taking an array of 256 bytes from 0x00 to 0xFF,
and rotating
0xEE and 0xEF to a position after the bytes 0xF0..0xF4. These rotated values
are shown in
boldface. When this rotation is performed on the initial bytes of UTF-8, it has
the effect of
making code points U+10000..U+10FFFF sort below U+E000..U+FFFF, thus mimicking
the ordering of UTF-16.
> Automaton Query/Filter (scalable regex)
> ---------------------------------------
>
> Key: LUCENE-1606
> URL: https://issues.apache.org/jira/browse/LUCENE-1606
> Project: Lucene - Java
> Issue Type: New Feature
> Components: Search
> Reporter: Robert Muir
> Assignee: Robert Muir
> Priority: Minor
> Fix For: 3.1
>
> Attachments: automaton.patch, automatonMultiQuery.patch,
> automatonmultiqueryfuzzy.patch, automatonMultiQuerySmart.patch,
> automatonWithWildCard.patch, automatonWithWildCard2.patch,
> BenchWildcard.java, LUCENE-1606-flex.patch, LUCENE-1606-flex.patch,
> LUCENE-1606.patch, LUCENE-1606.patch, LUCENE-1606.patch, LUCENE-1606.patch,
> LUCENE-1606.patch, LUCENE-1606.patch, LUCENE-1606.patch, LUCENE-1606.patch,
> LUCENE-1606_nodep.patch
>
>
> Attached is a patch for an AutomatonQuery/Filter (name can change if its not
> suitable).
> Whereas the out-of-box contrib RegexQuery is nice, I have some very large
> indexes (100M+ unique tokens) where queries are quite slow, 2 minutes, etc.
> Additionally all of the existing RegexQuery implementations in Lucene are
> really slow if there is no constant prefix. This implementation does not
> depend upon constant prefix, and runs the same query in 640ms.
> Some use cases I envision:
> 1. lexicography/etc on large text corpora
> 2. looking for things such as urls where the prefix is not constant (http://
> or ftp://)
> The Filter uses the BRICS package (http://www.brics.dk/automaton/) to convert
> regular expressions into a DFA. Then, the filter "enumerates" terms in a
> special way, by using the underlying state machine. Here is my short
> description from the comments:
> The algorithm here is pretty basic. Enumerate terms but instead of a
> binary accept/reject do:
>
> 1. Look at the portion that is OK (did not enter a reject state in the
> DFA)
> 2. Generate the next possible String and seek to that.
> the Query simply wraps the filter with ConstantScoreQuery.
> I did not include the automaton.jar inside the patch but it can be downloaded
> from http://www.brics.dk/automaton/ and is BSD-licensed.
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