viewdiff: save memory by eliminating two captures

Avoid relying on $DIGIT captures when @- and @+ to access
last match start and end, respectively.  The elimination of
the post capture ought to allow the use of sv_chop to advance
the string start pointer without memory copies.

This ought to save 1-2MB of memory on my system since I've
noticed the captures was using a big chunk of scratchpad
space.

1 files changed, 9 insertions, 9 deletions

diff --git a/lib/PublicInbox/ViewDiff.pm b/lib/PublicInbox/ViewDiff.pm
index 9a7adb57..95bbf2d2 100644
--- a/lib/PublicInbox/ViewDiff.pm
+++ b/lib/PublicInbox/ViewDiff.pm
@@ -154,16 +154,16 @@ sub diff_header ($$$) {
 
 sub diff_before_or_after ($$) {
         my ($ctx, $x) = @_;
-        if (exists $ctx->{-anchors} && $$x =~ /\A(.*?) # likely "---\n" # \$1
-                        # diffstat lines:
-                        ((?:^\x20(?:[^\n]+?)(?:\x20+\|\x20[^\n]*\n))+)
-                        (\x20[0-9]+\x20files?\x20)changed,
-                        (.*?)\z/msx) { # notes, commit message, etc
-                my @x = ($4, $3, $2, $1);
-                undef $$x;
+        if (exists $ctx->{-anchors} && $$x =~ # diffstat lines:
+                        /((?:^\x20(?:[^\n]+?)(?:\x20+\|\x20[^\n]*\n))+)
+                        (\x20[0-9]+\x20files?\x20)changed,/msx) {
+                my $pre = substr($$x, 0, $-[0]); # (likely) short prefix
+                substr($$x, 0, $+[0], ''); # sv_chop on $$x ($$x may be long)
+                my @x = ($2, $1);
                 my $lnk = $ctx->{-linkify};
                 my $zfh = $ctx->{zfh};
-                print $zfh $lnk->to_html(pop @x); # $1 uninteresting prefix
+                # uninteresting prefix
+                print $zfh $lnk->to_html($pre);
                 for my $l (split(/^/m, pop(@x))) { # $2 per-file stat lines
                         $l =~ /^ (.+)( +\| .*\z)/s and
                                 anchor0($ctx, $1, $2) and next;
@@ -173,7 +173,7 @@ sub diff_before_or_after ($$) {
                 print $zfh pop(@x), # $3 /^ \d+ files? /
                         qq(<a href="$ch">changed</a>,),
                         # insertions/deletions, notes, commit message, etc:
-                        $lnk->to_html(@x);
+                        $lnk->to_html($$x);
         } else {
                 print { $ctx->{zfh} } $ctx->{-linkify}->to_html($$x);
         }