regen/mk_invlists.pl: Collapse unused boundary values

Each Unicode property that specifies a boundary conditions, like
Word_Break, partitions all the Unicode code points into equivalence
classes.  So, for example, combining marks are placed into the Extend
class, because they are usually used to extend the previous character
and don't stand on their own.  mk_invlists.pl creates a boolean table of
all pairwise combinations of these classes, so that it knows by simple
lookup if the first character is class X and the next character is class
Y, if a break is permitted between these.

However, in some cases the answer isn't as simple as this, and other
means such as the characters in the vicinity of X and Y must be used to
disambiguate.  In these cases the table value in the cell (X,Y) isn't a
boolean, but is some other number indicating some specially crafted code
section to execute to resolve the issue.

Over the years, Unicode has tended to subdivide partitions into smaller
ones, as they've refined their algorithms.  But with Unicode 11, they
used another method and actually removed partitions.  Rather, they
retain the partitions, but no code point actually takes on the value of
an obsolete partition.

In order to not have to change the algorithm unnecessarily between
Unicode releases (who knows, they might change their minds, and
unobsolete these next time), mk_invlists has just kept the tables
around, but those cells won't ever get accessed because no code point in
the current release evaluates to them.

But that makes the tables unnecessarily large.  We can achieve the same
thing by mapping each unused equivalence class to the same value, which
we call 'unused'.  The algorithms that refer to the obsolete partitions
go through the data assigning values to the cells, but now the cells
overlap, since all obsolete classes map to the same row or column.  Thus
the data is total garbage.  But that doesn't matter, since that row or
column is never read by the data in the Unicode release the table is
constructed for.

mk_invlists also can compile older Unicode releases, and this makes
those tables smaller than before, with all unused classes in a
given release collapsed into a single row and single column of (unused)
garbage.

1 files changed, 1 insertions, 1 deletions

diff --git a/uni_keywords.h b/uni_keywords.h
index f71cd5c38f..590c158397 100644
--- a/uni_keywords.h
+++ b/uni_keywords.h
@@ -6994,6 +6994,6 @@ MPH_VALt match_uniprop( const unsigned char * const key, const U16 key_len ) {
  * 7bd6bcbe3813e0cd55e0998053d182b7bc8c97dcfd0b85028e9f7f55af4ad61b lib/unicore/version
  * 4bb677187a1a64e39d48f2e341b5ecb6c99857e49d7a79cf503bd8a3c709999b regen/charset_translations.pl
  * 03e51b0f07beebd5da62ab943899aa4934eee1f792fa27c1fb638c33bf4ac6ea regen/mk_PL_charclass.pl
- * a232f3394a90476c4c315c1d067d92243d0d0e38ed4e4bc8d4bb46978c45eaeb regen/mk_invlists.pl
+ * 97779934175e3b7dc8c302762e8e9f342bb828583dd7f862ed85be5906aa939c regen/mk_invlists.pl
  * c42c035b18a0426443184e9f889aa2b16bef5a9add9805cd853c4e2a783712ff regen/mph.pl
  * ex: set ro: */