diff --git a/luhn.dart b/luhn.dart
index d77849a..8641901 100644
--- a/luhn.dart
+++ b/luhn.dart
@@ -25,48 +25,37 @@ class Luhn {
     var i = 0;
     var digitCount = 0;
     var digits = [];
-    var matchFrom = -1;
     var len = s.length;
-    var maskOffset = -1;
-    var c = '';
-    var cc = 0;
     while (i < len) {
-      c = s[i];
-      cc = c.charCodeAt(0);
+      var c = s[i];
+      var cc = c.charCodeAt(0);
       if (cc >= C_0 && cc <= C_9) {
-        if (matchFrom < 0) { matchFrom = i; }
         digitCount += 1;
         digits.add(Math.parseInt(c));
         if (digitCount >= 14) {
-          for (var theLen = 14; theLen <= 16 && theLen <= digitCount; theLen++) {
-            var startAt = digitCount - 14;
-            if (theLen >= 16) {
-              startAt -= 2;
-            } else if (theLen >= 15) {
-              startAt -= 1;
-            }
+          for (var theLen = digitCount < 16 ? digitCount : 16; theLen >= 14; theLen--) {
+            var startAt = digitCount - theLen;
             if (testIt(digits, startAt, theLen)) {
               if (masked === null) { masked = s.splitChars(); }
               var j = i;
-              while (j >= matchFrom && j > maskOffset) {
+              var maskLen = theLen;
+              while (maskLen > 0) {
                 var mc = s.charCodeAt(j);
                 if (mc >= C_0 && mc <= C_9) {
                   masked[j] = 'X';
+                  maskLen -= 1;
                 }
                 j -= 1;
               }
-              maskOffset = i;
             }
           }
         }
-        if (digitCount >= 16) { matchFrom += 1; }
       } else if (c == '-' || c == ' ') {
         // Keep going.
       } else {
         if (digitCount > 0) {
           digitCount = 0;
           digits = [];
-          matchFrom = -1;
         }
       }
       i += 1;
diff --git a/luhn.rb b/luhn.rb
index b8a2096..20c076e 100644
--- a/luhn.rb
+++ b/luhn.rb
@@ -22,9 +22,7 @@ def mask s
     i = 0
     digit_count = 0
     digits = []
-    max_len = 0
     len = s.length
-    c = ''
     while i < len
       c = s[i]
       case c
@@ -32,15 +30,9 @@ def mask s
         digit_count += 1
         digits << c.to_i
         if digit_count >= 14
-          max_len = digit_count > 16 ? 16 : digit_count
-          the_len = 14
-          while the_len <= max_len
-            start_at = digit_count - 14
-            if the_len >= 16
-              start_at -= 2
-            elsif the_len >= 15
-              start_at -= 1
-            end
+          the_len = digit_count < 16 ? digit_count : 16
+          while the_len >= 14
+            start_at = digit_count - the_len
             if test_it(digits, start_at, the_len)
               masked = s[0..-1] if not masked
               mask_len = the_len
@@ -54,7 +46,7 @@ def mask s
                 j -= 1
               end
             end
-            the_len += 1
+            the_len -= 1
           end
         end
       when '-', ' '
diff --git a/mask.sh b/mask.sh
index 5daac07..b7eae69 100755
--- a/mask.sh
+++ b/mask.sh
@@ -2,5 +2,5 @@
 
 # Call your program here instead of cat.
 #cat
-./luhny.rb
-#./luhny.dart
+#./luhny.rb
+./luhny.dart