Added ndpi_data_window_variance() and ndpi_data_window_stddev() API calls

2 files changed, 31 insertions, 1 deletions

diff --git a/src/include/ndpi_api.h.in b/src/include/ndpi_api.h.in
index c272d66c8..5d77d6221 100644
--- a/src/include/ndpi_api.h.in
+++ b/src/include/ndpi_api.h.in
@@ -1030,9 +1030,13 @@ extern "C" {
   void ndpi_free_data_analysis(struct ndpi_analyze_struct *d);
   void ndpi_data_add_value(struct ndpi_analyze_struct *s, const u_int32_t value);
 
-  float ndpi_data_average(struct ndpi_analyze_struct *s);
+  /* Sliding-window only */
   float ndpi_data_window_average(struct ndpi_analyze_struct *s);
+  float ndpi_data_window_variance(struct ndpi_analyze_struct *s);
+  float ndpi_data_window_stddev(struct ndpi_analyze_struct *s);
 
+  /* All data */
+  float ndpi_data_average(struct ndpi_analyze_struct *s);
   float ndpi_data_entropy(struct ndpi_analyze_struct *s);
   float ndpi_data_variance(struct ndpi_analyze_struct *s);
   float ndpi_data_stddev(struct ndpi_analyze_struct *s);
diff --git a/src/lib/ndpi_analyze.c b/src/lib/ndpi_analyze.c
index 4b4fbf72b..7d4aa5f47 100644
--- a/src/lib/ndpi_analyze.c
+++ b/src/lib/ndpi_analyze.c
@@ -157,6 +157,32 @@ float ndpi_data_window_average(struct ndpi_analyze_struct *s) {
 
 /* ********************************************************************************* */
 
+/* Compute the variance only on the sliding window */
+float ndpi_data_window_variance(struct ndpi_analyze_struct *s) {
+  if(s->num_values_array_len) {
+    float   sum = 0.0, avg = ndpi_data_window_average(s);
+    u_int16_t i, n = ndpi_min(s->num_data_entries, s->num_values_array_len);
+
+    if(n == 0)
+      return(0);
+    
+    for(i=0; i<n; i++)
+      sum += pow(s->values[i]-avg, 2);
+
+    return((float)sum / (float)n);
+  } else
+    return(0);
+}
+
+/* ********************************************************************************* */
+
+/* Compute the variance only on the sliding window */
+float ndpi_data_window_stddev(struct ndpi_analyze_struct *s) {
+  return(sqrt(ndpi_data_window_variance(s)));
+}
+
+  /* ********************************************************************************* */
+
 /*
   Compute entropy on the last sliding window values
 */