diff --git a/exprtk_simple_example_13.cpp b/exprtk_simple_example_13.cpp
index 192096d..aafe6fb 100644
--- a/exprtk_simple_example_13.cpp
+++ b/exprtk_simple_example_13.cpp
@@ -30,7 +30,7 @@ void savitzky_golay_filter()
    typedef exprtk::expression<T>     expression_t;
    typedef exprtk::parser<T>             parser_t;
 
-   std::string gsfilter_program =
+   std::string sgfilter_program =
                   " var weight[9] :=                                  "
                   "       {                                           "
                   "         -21, 14,  39,                             "
@@ -38,20 +38,27 @@ void savitzky_golay_filter()
                   "          39, 14, -21                              "
                   "       };                                          "
                   "                                                   "
-                  " var lower_bound := trunc(weight[] / 2);           "
-                  " var upper_bound := v_in[] - lower_bound;          "
-                  "                                                   "
                   " if (v_in[] >= weight[])                           "
                   " {                                                 "
+                  "   var lower_bound := trunc(weight[] / 2);         "
+                  "   var upper_bound := v_in[] - lower_bound;        "
+                  "                                                   "
                   "   for (i := lower_bound; i < upper_bound; i += 1) "
                   "   {                                               "
                   "     v_out[i] := 0;                                "
                   "     for (j := 0; j < weight[]; j += 1)            "
                   "     {                                             "
-                  "       v_out[i] += weight[j] * v_in[i + j];        "
+                  "       var index := i + j - lower_bound;           "
+                  "       v_out[i] += weight[j] * v_in[index];        "
                   "     };                                            "
                   "     v_out[i] /= 231;                              "
                   "   };                                              "
+                  "                                                   "
+                  "   for (i := 0; i < lower_bound; i += 1)           "
+                  "   {                                               "
+                  "     v_out[i] := 0;                                "
+                  "     v_out[v_out[] - i - 1] := 0;                  "
+                  "   };                                              "
                   " }                                                 ";
 
    const std::size_t n = 1024;
@@ -81,7 +88,7 @@ void savitzky_golay_filter()
 
    parser_t parser;
 
-   parser.compile(gsfilter_program,expression);
+   parser.compile(sgfilter_program,expression);
 
    expression.value();
 
diff --git a/readme.txt b/readme.txt
index 748df97..d95b907 100644
--- a/readme.txt
+++ b/readme.txt
@@ -261,6 +261,9 @@ of C++ compilers:
 |          | r0 < r1. If x is within the range it will snap to the   |
 |          | closest bound. (eg: iclamp(r0,x,r1)                     |
 +----------+---------------------------------------------------------+
+| inrange  | In-range returns 'true' when x is within the range r0   |
+|          | and r1. Where r0 < r1.  (eg: inrange(r0,x,r1)           |
++----------+---------------------------------------------------------+
 | log      | Natural logarithm of x.  (eg: log(x))                   |
 +----------+---------------------------------------------------------+
 | log10    | Base 10 logarithm of x.  (eg: log10(x))                 |