sourcestats: include precision in weight calculation

In order to stabilize the weights of refclock samples which have only
slightly different distances, don't allow the stddev value used in the
weight calculation to be smaller than the precision and also assign
weight of 1 to all samples which have distance < minimum + precision.

diff --git a/sourcestats.c b/sourcestats.c
index d8d42462bc306a158ca84f12b7f00c639f7ffa5c..a18b8b25d3dfd16b2fa682984112878b5a2884ae 100644 (file)
--- a/sourcestats.c
+++ b/sourcestats.c
@@ -51,9 +51,6 @@
 #define MIN_SKEW 1.0e-12
 #define MAX_SKEW 1.0e+02
 
-/* The minimum assumed std dev for weighting */
-#define MIN_WEIGHT_SD 1.0e-9
-
 /* The asymmetry of network jitter when all jitter is in one direction */
 #define MAX_ASYMMETRY 0.5
 
@@ -489,6 +486,7 @@ SST_DoNewRegression(SST_Stats inst)
   double min_distance, mean_distance;
   double sd_weight, sd;
   double old_skew, old_freq, stress;
+  double precision;
 
   convert_to_intervals(inst, times_back + inst->runs_samples);
 
@@ -510,11 +508,15 @@ SST_DoNewRegression(SST_Stats inst)
 
     /* And now, work out the weight vector */
 
-    sd = mean_distance - min_distance;
-    sd = CLAMP(MIN_WEIGHT_SD, sd, min_distance);
+    precision = LCL_GetSysPrecisionAsQuantum();
+    sd = (mean_distance - min_distance) / SD_TO_DIST_RATIO;
+    sd = CLAMP(precision, sd, min_distance);
+    min_distance += precision;
 
     for (i=0; i<inst->n_samples; i++) {
-      sd_weight = 1.0 + SD_TO_DIST_RATIO * (peer_distances[i] - min_distance) / sd;
+      sd_weight = 1.0;
+      if (peer_distances[i] > min_distance)
+        sd_weight += (peer_distances[i] - min_distance) / sd;
       weights[i] = sd_weight * sd_weight;
     }
   }