From 97973476dd225680059f6b58a12cef3ef950ffde Mon Sep 17 00:00:00 2001
From: Mischa POSLAWSKY <perl@shiar.org>
Date: Sun, 15 Nov 2009 07:06:01 +0100
Subject: [PATCH] cleanup context variables

---
 lib/List/Index.pm | 25 ++++++++++++-------------
 t/10-ranges.t     |  4 ++--
 2 files changed, 14 insertions(+), 15 deletions(-)

diff --git a/lib/List/Index.pm b/lib/List/Index.pm
index daeb707..6309d2e 100644
--- a/lib/List/Index.pm
+++ b/lib/List/Index.pm
@@ -27,14 +27,17 @@ sub ranges {
 	my $pages    = $options->{pages   } || 1 + int $#rows / $pagesize;
 
 	$pagesize = $pages >= $#rows ? 1 : @rows / $pages;
-	my $lookbehind = -$context;
-	my $lookahead  =  $context;
+	my $shrunk = 0;
+	my $enlarged = 0;
 
 	my @links = ('');
 	for (my $offset = $pagesize + .5; $offset < @rows; $offset += $pagesize) {
 		my $link = substr $rows[$offset], 0, $length;
 		if ($context) {
-			my $penalty = 0;
+			my $lookbehind = -$context + $shrunk;
+			my $lookahead  =  $context - $enlarged;
+			$shrunk = $enlarged = 0;
+
 			# take a value slightly before the current offset
 			if ((my $before = $offset + $lookbehind) > 0) {
 				# see how much of it matches the current link
@@ -46,15 +49,13 @@ sub ranges {
 				# truncate link upto where the earlier value starts to differ
 				if ($trim < length $link) {
 					substr($link, $trim) = '';
-					for (reverse $before .. $offset) {
-						$rows[$offset - $penalty] =~ /^\Q$link/ or last;
-						$penalty++;
+					for (reverse $before .. $offset - 1) {
+						$rows[$_] =~ /^\Q$link/ or last;
+						$enlarged++;
 					}
 				}
 			}
 
-			$lookbehind = -$context;
-
 			# take a value after the current offset
 			if ((my $after = $offset + $lookahead) < $#rows) {
 				# see how much of it matches the current link
@@ -67,15 +68,13 @@ sub ranges {
 				if ($trim < length $link) {
 					$link = substr $rows[$after], 0, $trim;
 					# advance lookbehind offset on the next page
-					$penalty = 0;
-					for ($offset .. $after) {
+					$enlarged = 0;
+					for ($offset + 1 .. $after) {
+						$shrunk++;
 						last if $rows[$_] =~ /^\Q$link/;
-						$lookbehind++;
 					}
 				}
 			}
-
-			$lookahead = $context - $penalty;
 		}
 
 		push @links, $link unless $links[-1] eq $link;
diff --git a/t/10-ranges.t b/t/10-ranges.t
index efe64b3..a394945 100644
--- a/t/10-ranges.t
+++ b/t/10-ranges.t
@@ -133,12 +133,12 @@ subtest 'distribution' => sub {
 	my $index = List::Index->new({ pagesize => 10 }) or return;
 
 	is_deeply(
-		$index->ranges(\@data, { context => 8 }),
+		$index->ranges(\@data, { context => 7 }),
 		[qw(-g h i-)],
 		'large context'
 	);
 	is_deeply(
-		$index->ranges(\@data, { context => 7 }),
+		$index->ranges(\@data, { context => 6 }),
 		# after 2nd page is enlarged by lookbehind to 'h', limit subsequent lookahead
 		# to prevent the page from getting too large (17 entries if forwarded to 'i')
 		[qw(-g h-hm hn-)],
-- 
2.30.0