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.

diff --git a/lib/PublicInbox/ViewDiff.pm b/lib/PublicInbox/ViewDiff.pm
index 9a7adb57770f5843892438644eea38067c24e483..95bbf2d2a7da79c78948439c687525b82fc4eba4 100644 (file)
--- 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);
        }