fix pagesize < 1

[perl/list-index.git] / lib / List / Index.pm

diff --git a/lib/List/Index.pm b/lib/List/Index.pm
index 339bd7d8710b6ede1e44fef6b207d28e0e26f766..e67e5ae730202bafb8bd4ff3640d35656b51c129 100644 (file)
--- a/lib/List/Index.pm
+++ b/lib/List/Index.pm
@@ -22,45 +22,56 @@ sub ranges {
        my $length   = $options->{length  } || 4;
        my $pages    = $options->{pages   } || 1 + int $#$self / $pagesize;
 
-       $pagesize = @$self / $pages;
+       $pagesize = $pages >= $#$self ? 1 : @$self / $pages;
        my $offset = $pagesize + .5;
-       my $penalty = 0;
+       my $lookbehind = -$context;
+       my $lookahead  =  $context;
        my @links = ('');
        while ($offset < @$self) {
                my $link = substr $self->[$offset], 0, $length;
                if ($context) {
-                       if ($offset > $context - 1 + $penalty) {
-                               # take a value slightly before the current offset
-                               my $before = $self->[$offset - $context - 1 + $penalty];
+                       my $penalty = 0;
+                       # take a value slightly before the current offset
+                       if ((my $before = $offset + $lookbehind) > 0) {
                                # see how much of it matches the current link
                                my $trim = 1;
-                               for my $match (split //, $before) {
+                               for my $match (split //, $self->[$before - 1]) {
                                        scalar $link =~ /\G\Q$match/g or last;
                                        $trim++;
                                }
                                # truncate link upto where the earlier value starts to differ
-                               substr($link, $trim) = '' unless $trim > length $link;
+                               if ($trim < length $link) {
+                                       substr($link, $trim) = '';
+                                       for (reverse $before .. $offset) {
+                                               $self->[$offset - $penalty] =~ /^\Q$link/ or last;
+                                               $penalty++;
+                                       }
+                               }
                        }
 
-                       $penalty = 0;
-                       if ($offset + $context < $#$self) {
-                               # take a value after the current offset
-                               my $after = $self->[$offset + $context];
+                       $lookbehind = -$context;
+
+                       # take a value after the current offset
+                       if ((my $after = $offset + $lookahead) < $#$self) {
                                # see how much of it matches the current link
                                my $trim = 1;
-                               for my $match (split //, $after) {
+                               for my $match (split //, $self->[$after]) {
                                        scalar $link =~ /\G\Q$match/g or last;
                                        $trim++;
                                }
                                # use this link if it's shorter
                                if ($trim < length $link) {
-                                       $link = substr $after, 0, $trim;
-                                       for ($offset .. $#$self) {
-                                               last if $self->[$offset + $penalty] =~ /^\Q$link/;
-                                               $penalty++;
+                                       $link = substr $self->[$after], 0, $trim;
+                                       # advance lookbehind offset on the next page
+                                       $penalty = 0;
+                                       for ($offset .. $after) {
+                                               last if $self->[$_] =~ /^\Q$link/;
+                                               $lookbehind++;
                                        }
                                }
                        }
+
+                       $lookahead = $context - $penalty;
                }
 
                push @links, $link;