[PATCH 3/3] git: reduce stat buffer storage overhead

[Eric Wong <e@yhbt.net>]

The stat() array is a whopping 480 bytes (on x86-64, Perl 5.28),
while the new packed representation of two 64-bit doubles as a
scalar is "only" 56 bytes.  This can add up when there's many
inboxes.  Just use a string comparison on the packed
representation.

Some 32-bit Perl builds (IIRC OpenBSD) lack quad support, so
doubles were chosen for pack() portability.
---
 lib/PublicInbox/Git.pm | 13 ++++++-------
 1 file changed, 6 insertions(+), 7 deletions(-)

diff --git a/lib/PublicInbox/Git.pm b/lib/PublicInbox/Git.pm
index 9c96b3f0..8410b2fc 100644
--- a/lib/PublicInbox/Git.pm
+++ b/lib/PublicInbox/Git.pm
@@ -55,10 +55,8 @@ sub git_quote ($) {
 
 sub new {
 	my ($class, $git_dir) = @_;
-	my @st;
-	$st[7] = $st[10] = 0;
 	# may contain {-tmp} field for File::Temp::Dir
-	bless { git_dir => $git_dir, st => \@st, -git_path => {} }, $class
+	bless { git_dir => $git_dir, alt_st => '', -git_path => {} }, $class
 }
 
 sub git_path ($$) {
@@ -79,10 +77,11 @@ sub alternates_changed {
 	my ($self) = @_;
 	my $alt = git_path($self, 'objects/info/alternates');
 	my @st = stat($alt) or return 0;
-	my $old_st = $self->{st};
-	# 10 - ctime, 7 - size
-	return 0 if ($st[10] == $old_st->[10] && $st[7] == $old_st->[7]);
-	$self->{st} = \@st;
+
+	# can't rely on 'q' on some 32-bit builds, but `d' works
+	my $st = pack('dd', $st[10], $st[7]); # 10: ctime, 7: size
+	return 0 if $self->{alt_st} eq $st;
+	$self->{alt_st} = $st; # always a true value
 }
 
 sub last_check_err {