Revert "regcomp.c: Add a constant 0 element before inversion lists"

This reverts commit 533c4e2f08b42d977e5004e823d4849f7473d2d0.
This continues the backing out of this topic branch.  A bisect shows
that the first commit exhibiting an error is the first one in the
branch.

1 files changed, 18 insertions, 9 deletions

diff --git a/regen/mk_invlists.pl b/regen/mk_invlists.pl
index 27c080233c..67b6e417fc 100644
--- a/regen/mk_invlists.pl
+++ b/regen/mk_invlists.pl
@@ -15,7 +15,7 @@ require 'regen/regen_lib.pl';
 # in the headers is used to minimize the possibility of things getting
 # out-of-sync, or the wrong data structure being passed.  Currently that
 # random number is:
-my $VERSION_DATA_STRUCTURE_TYPE = 1039476070;
+my $VERSION_DATA_STRUCTURE_TYPE = 290655244;
 
 my $out_fh = open_new('charclass_invlists.h', '>',
 		      {style => '*', by => $0,
@@ -36,18 +36,27 @@ sub output_invlist ($$) {
     # Output the inversion list $invlist using the name $name for it.
     # It is output in the exact internal form for inversion lists.
 
-    # Is the last element of the header 0, or 1 ?
-    my $zero_or_one = 0;
-    my $count = @$invlist;
-    if ($invlist->[0] != 0) {
-        unshift @$invlist, 0;
+    my $zero_or_one;    # Is the last element of the header 0, or 1 ?
+
+    # If the first element is 0, it goes in the header, instead of the body
+    if ($invlist->[0] == 0) {
+        shift @$invlist;
+
+        $zero_or_one = 0;
+
+        # Add a dummy 0 at the end so that the length is constant.  inversion
+        # lists are always stored with enough room so that if they change from
+        # beginning with 0, they don't have to grow.
+        push @$invlist, 0;
+    }
+    else {
         $zero_or_one = 1;
     }
 
     print $out_fh "\n#ifndef PERL_IN_XSUB_RE\n" unless exists $include_in_ext_re{$name};
     print $out_fh "\nstatic UV ${name}_invlist[] = {\n";
 
-    print $out_fh "\t$count,\t/* Number of elements */\n";
+    print $out_fh "\t", scalar @$invlist, ",\t/* Number of elements */\n";
 
     # This should be UV_MAX, but I (khw) am not confident that the suffixes
     # for specifying the constant are portable, e.g.  'ull' on a 32 bit
@@ -56,8 +65,8 @@ sub output_invlist ($$) {
     print $out_fh "\t0,\t/* Cache of previous search index result */\n";
     print $out_fh "\t$VERSION_DATA_STRUCTURE_TYPE, /* Version and data structure type */\n";
     print $out_fh "\t", $zero_or_one,
-                  ",\t/* 0 if the list starts at 0;",
-                  "\n\t\t   1 if it starts at the element beyond 0 */\n";
+                  ",\t/* 0 if this is the first element of the list proper;",
+                  "\n\t\t   1 if the next element is the first */\n";
 
     # The main body are the UVs passed in to this routine.  Do the final
     # element separately