faster.diff

diff --git a/lib/kpeg/compiled_parser.rb b/lib/kpeg/compiled_parser.rb
index ff82467..eb16e32 100644
--- a/lib/kpeg/compiled_parser.rb
+++ b/lib/kpeg/compiled_parser.rb
@@ -51,6 +51,12 @@ module KPeg
       @string = string
       @string_size = string ? string.size : 0
       @pos = pos
+
+      if string
+        @chars = string.chars
+      else
+        @chars = []
+      end
     end
 
     def show_pos
@@ -163,8 +169,7 @@ module KPeg
         if @pos >= @string_size
           return nil
         end
-
-        s = @string[@pos].ord
+        s = @chars[@pos].ord
         @pos += 1
         s
       end
diff --git a/lib/kpeg/format_parser.rb b/lib/kpeg/format_parser.rb
index 4f84e94..7b6035a 100644
--- a/lib/kpeg/format_parser.rb
+++ b/lib/kpeg/format_parser.rb
@@ -56,6 +56,12 @@ class KPeg::FormatParser
       @string = string
       @string_size = string ? string.size : 0
       @pos = pos
+
+      if string
+        @chars = string.chars
+      else
+        @chars = []
+      end
     end
 
     def show_pos
@@ -168,8 +174,7 @@ class KPeg::FormatParser
         if @pos >= @string_size
           return nil
         end
-
-        s = @string[@pos].ord
+        s = @chars[@pos].ord
         @pos += 1
         s
       end
diff --git a/lib/kpeg/string_escape.rb b/lib/kpeg/string_escape.rb
index 99f8373..bcd49ca 100644
--- a/lib/kpeg/string_escape.rb
+++ b/lib/kpeg/string_escape.rb
@@ -64,6 +64,12 @@ class KPeg::StringEscape
       @string = string
       @string_size = string ? string.size : 0
       @pos = pos
+
+      if string
+        @chars = string.chars
+      else
+        @chars = []
+      end
     end
 
     def show_pos
@@ -176,8 +182,7 @@ class KPeg::StringEscape
         if @pos >= @string_size
           return nil
         end
-
-        s = @string[@pos].ord
+        s = @chars[@pos].ord
         @pos += 1
         s
       end