X-Git-Url: http://git.shiar.nl/perl/list-index.git/blobdiff_plain/b9c565b77b8ac8f8856c6af118a1e1af5b917c24..e2a186365224032ff37caac824d50c9b43130952:/lib/List/Index.pm

diff --git a/lib/List/Index.pm b/lib/List/Index.pm
index daeb707..35f0549 100644
--- a/lib/List/Index.pm
+++ b/lib/List/Index.pm
@@ -24,17 +24,20 @@ sub ranges {
 	my $pagesize = $options->{pagesize} || 50;
 	my $context  = $options->{context } // 1 + ($pagesize >> 4);
 	my $length   = $options->{length  } || 4;
-	my $pages    = $options->{pages   } || 1 + int $#rows / $pagesize;
+	my $pages    = $options->{pages   } || 1 + int($#rows / $pagesize);
 
-	$pagesize = $pages >= $#rows ? 1 : @rows / $pages;
-	my $lookbehind = -$context;
-	my $lookahead  =  $context;
+	$pagesize = $pages >= @rows ? 1 : @rows / $pages;
+	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 + $lookbehind) > 0) {
 				# see how much of it matches the current link
@@ -46,36 +49,35 @@ sub ranges {
 				# truncate link upto where the earlier value starts to differ
 				if ($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
 				my $trim = 1;
+				pos $link = 0;
 				for my $match (split //, $rows[$after]) {
 					scalar $link =~ /\G\Q$match/g or last;
 					$trim++;
 				}
 				# use this link if it's shorter
 				if ($trim < length $link) {
-					$link = substr $rows[$after], 0, $trim;
-					# advance lookbehind offset on the next page
-					$penalty = 0;
-					for ($offset .. $after) {
-						last if $rows[$_] =~ /^\Q$link/;
-						$lookbehind++;
+					$enlarged = 0;
+					for ($offset + 1 .. $after) {
+						my $prefix = substr $rows[$_], 0, $trim;
+						# advance lookbehind offset on the next page
+						$shrunk++;
+						next if $link =~ /^\Q$prefix/;
+						$link = $prefix;
+						last;
 					}
 				}
 			}
-
-			$lookahead = $context - $penalty;
 		}
 
 		push @links, $link unless $links[-1] eq $link;