From 1331e0aec90f5a648371eee1a3a1117669485a11 Mon Sep 17 00:00:00 2001
From: Luca Deri <deri@ntop.org>
Date: Tue, 9 Feb 2021 15:56:03 +0100
Subject: Extended the API to calculate jitter

- ndpi_jitter_init()
- ndpi_jitter_free()
- ndpi_jitter_add_value()
---
 example/ndpiReader.c        | 20 +++++++++++++++
 src/include/ndpi_api.h.in   |  6 +++++
 src/include/ndpi_typedefs.h |  8 ++++++
 src/lib/ndpi_analyze.c      | 62 +++++++++++++++++++++++++++++++++++++++++++++
 4 files changed, 96 insertions(+)

diff --git a/example/ndpiReader.c b/example/ndpiReader.c
index f837a5c29..a2caeaad9 100644
--- a/example/ndpiReader.c
+++ b/example/ndpiReader.c
@@ -3765,6 +3765,25 @@ void hwUnitTest() {
 
 /* *********************************************** */
 
+void jitterUnitTest() {
+  struct ndpi_jitter_struct jitter;
+  float v[] = { 10, 14, 8, 25, 16, 22, 14, 35, 15, 27, 218, 40, 28, 40, 25, 65 };
+  u_int i, num = sizeof(v) / sizeof(float);
+  u_int num_learning_points = 4;
+  u_int8_t trace = 0;
+  
+  assert(ndpi_jitter_init(&jitter, num_learning_points) == 0);
+
+  for(i=0; i<num; i++) {
+    float rc = ndpi_jitter_add_value(&jitter, v[i]);
+				     
+    if(trace)
+      printf("%2u)\t%.3f\t%.3f\n", i, v[i], rc);
+  }
+}
+
+/* *********************************************** */
+
 /**
    @brief MAIN FUNCTION
 **/
@@ -3788,6 +3807,7 @@ int orginal_main(int argc, char **argv) {
     /* Internal checks */    
     // binUnitTest();
     hwUnitTest();
+    jitterUnitTest();
     rsiUnitTest();
     hashUnitTest();
     dgaUnitTest();
diff --git a/src/include/ndpi_api.h.in b/src/include/ndpi_api.h.in
index 5e2082bbd..6ecae02d2 100644
--- a/src/include/ndpi_api.h.in
+++ b/src/include/ndpi_api.h.in
@@ -1404,6 +1404,12 @@ extern "C" {
 
   /* ******************************* */
 
+  int   ndpi_jitter_init(struct ndpi_jitter_struct *hw, u_int16_t num_periods);
+  void  ndpi_jitter_free(struct ndpi_jitter_struct *hw);
+  float ndpi_jitter_add_value(struct ndpi_jitter_struct *s, const float value);
+
+  /* ******************************* */
+
   const char* ndpi_data_ratio2str(float ratio);
 
   void ndpi_data_print_window_values(struct ndpi_analyze_struct *s); /* debug */
diff --git a/src/include/ndpi_typedefs.h b/src/include/ndpi_typedefs.h
index 7656cb603..6bccd0e77 100644
--- a/src/include/ndpi_typedefs.h
+++ b/src/include/ndpi_typedefs.h
@@ -1553,6 +1553,14 @@ struct ndpi_rsi_struct {
 
 /* **************************************** */
 
+struct ndpi_jitter_struct {
+  u_int8_t empty:1, jitter_ready:1, _notused:6;
+  u_int16_t num_values, next_index;
+  float *observations, last_value, jitter_total;
+};
+
+/* **************************************** */
+
 typedef struct ndpi_ptree ndpi_ptree_t;
 
 /* **************************************** */
diff --git a/src/lib/ndpi_analyze.c b/src/lib/ndpi_analyze.c
index d4966791e..2f21dde78 100644
--- a/src/lib/ndpi_analyze.c
+++ b/src/lib/ndpi_analyze.c
@@ -1058,3 +1058,65 @@ int ndpi_hw_add_value(struct ndpi_hw_struct *hw, const u_int32_t _value, double
     return(1); /* We're in business: forecast is meaningful now */
   }
 }
+
+/* ********************************************************************************* */
+/* ********************************************************************************* */
+
+/*
+  Jitter calculator
+  
+  Used to determine how noisy is a signal
+*/
+
+int ndpi_jitter_init(struct ndpi_jitter_struct *s, u_int16_t num_learning_values) {
+  memset(s, 0, sizeof(struct ndpi_jitter_struct));
+
+  if(num_learning_values < 2) num_learning_values = 2;
+  
+  s->empty = 1, s->num_values = num_learning_values;
+  s->observations = (float*)ndpi_calloc(num_learning_values, sizeof(float));
+
+  if(s->observations) {
+    s->last_value = 0;
+    return(0);
+  } else
+    return(-1);  
+}
+
+/* ************************************* */
+
+void ndpi_free_jitter(struct ndpi_jitter_struct *s) {
+  ndpi_free(s->observations);
+}
+
+/* ************************************* */
+
+/*
+  This function adds a new value and returns the computed Jitter
+*/
+float ndpi_jitter_add_value(struct ndpi_jitter_struct *s, const float value) {
+  float val = fabsf(value - s->last_value);
+
+  if(s->empty && (s->next_index == 0))
+    ; /* Skip the first value as we are unable to calculate the difference */
+  else {
+    s->jitter_total -= s->observations[s->next_index];
+    s->observations[s->next_index] = val;
+    s->jitter_total += val;
+  }
+  
+  s->last_value = value, s->next_index = (s->next_index + 1) % s->num_values;
+  if(s->next_index == 0) s->jitter_ready = 1; /* We have completed one round */
+
+#ifdef DEBUG_JITTER
+  printf("[JITTER] [value: %.3f][diff: %.3f][jitter_total: %.3f] -> %.3f\n",
+	 value, val, s->jitter_total,
+	 s->jitter_ready ? (s->jitter_total / s->num_values) : -1);
+#endif
+  
+  if(!s->jitter_ready)
+    return(-1); /* Too early */
+  else 
+    return(s->jitter_total / s->num_values);
+}
+
-- 
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