src/utils_latency.[ch]: get_rate(): Make lower bound exclusive.

[collectd.git] / src / utils_latency.c

diff --git a/src/utils_latency.c b/src/utils_latency.c
index 24234f8..f5a51e2 100644 (file)
--- a/src/utils_latency.c
+++ b/src/utils_latency.c
@@ -293,50 +293,47 @@ cdtime_t latency_counter_get_percentile (latency_counter_t *lc, /* {{{ */
 double latency_counter_get_rate (const latency_counter_t *lc, /* {{{ */
         cdtime_t lower, cdtime_t upper, const cdtime_t now)
 {
-  cdtime_t lower_bin;
-  cdtime_t upper_bin;
-  double sum = 0;
-
   if ((lc == NULL) || (lc->num == 0))
-    return (0);
+    return (NAN);
 
   if (upper && (upper < lower))
+    return (NAN);
+  if (lower == upper)
     return (0);
 
   /* Buckets have an exclusive lower bound and an inclusive upper bound. That
    * means that the first bucket, index 0, represents (0-bin_width]. That means
-   * that lower==bin_width needs to result in lower_bin=0, hence the -1. */
+   * that latency==bin_width needs to result in bin=0, that's why we need to
+   * subtract one before dividing by bin_width. */
+  cdtime_t lower_bin = 0;
   if (lower)
-    lower_bin = (lower - 1) / lc->bin_width;
-  else
-    lower_bin = 0;
+    /* lower is *exclusive* => determine bucket for lower+1 */
+    lower_bin = ((lower+1) - 1) / lc->bin_width;
 
+  /* lower is greater than the longest latency observed => rate is zero. */
+  if (lower_bin >= HISTOGRAM_NUM_BINS)
+    return (0);
+
+  cdtime_t upper_bin = HISTOGRAM_NUM_BINS - 1;
   if (upper)
     upper_bin = (upper - 1) / lc->bin_width;
-  else
-    upper_bin = HISTOGRAM_NUM_BINS - 1;
-
-  if (lower_bin >= HISTOGRAM_NUM_BINS)
-    lower_bin = HISTOGRAM_NUM_BINS - 1;
 
   if (upper_bin >= HISTOGRAM_NUM_BINS) {
     upper_bin = HISTOGRAM_NUM_BINS - 1;
     upper = 0;
   }
 
-  sum = 0;
+  double sum = 0;
   for (size_t i = lower_bin; i <= upper_bin; i++)
-  {
     sum += lc->histogram[i];
-  }
 
   if (lower) {
     /* Approximate ratio of requests in lower_bin, that fall between
      * lower_bin_boundary and lower. This ratio is then subtracted from sum to
      * increase accuracy. */
     cdtime_t lower_bin_boundary = lower_bin * lc->bin_width;
-    assert (lower > lower_bin_boundary);
-    double lower_ratio = (double)(lower - lower_bin_boundary - 1) / ((double) lc->bin_width);
+    assert (lower >= lower_bin_boundary);
+    double lower_ratio = (double)(lower - lower_bin_boundary) / ((double) lc->bin_width);
     sum -= lower_ratio * lc->histogram[lower_bin];
   }