From 7547192fa2665f98b34bf30d89fbf034c1267816 Mon Sep 17 00:00:00 2001
From: Andrew Kryczka <andrewkr@fb.com>
Date: Thu, 31 Aug 2017 15:41:30 -0700
Subject: [PATCH 1/2] fix inclusive-exclusiveness of histogram ToString

---
 monitoring/histogram.cc      | 3 ++-
 monitoring/histogram_test.cc | 9 +++++++++
 2 files changed, 11 insertions(+), 1 deletion(-)

diff --git a/monitoring/histogram.cc b/monitoring/histogram.cc
index b3c01a78e08..d2b7ff8442c 100644
--- a/monitoring/histogram.cc
+++ b/monitoring/histogram.cc
@@ -209,7 +209,8 @@ std::string HistogramStat::ToString() const {
     if (bucket_value <= 0.0) continue;
     cumulative_sum += bucket_value;
     snprintf(buf, sizeof(buf),
-             "[ %7" PRIu64 ", %7" PRIu64 " ) %8" PRIu64 " %7.3f%% %7.3f%% ",
+             "%c %7" PRIu64 ", %7" PRIu64 " ] %8" PRIu64 " %7.3f%% %7.3f%% ",
+             (b == 0) ? '[' : '(',
              (b == 0) ? 0 : bucketMapper.BucketLimit(b-1),  // left
               bucketMapper.BucketLimit(b),  // right
               bucket_value,                   // count
diff --git a/monitoring/histogram_test.cc b/monitoring/histogram_test.cc
index b4e3c981c8e..950e6c80e76 100644
--- a/monitoring/histogram_test.cc
+++ b/monitoring/histogram_test.cc
@@ -85,6 +85,15 @@ TEST_F(HistogramTest, BasicOperation) {
   BasicOperation(histogramWindowing);
 }
 
+TEST_F(HistogramTest, BoundaryValue) {
+  HistogramImpl histogram;
+  // both should be in [0, 1], never (1, 2].
+  histogram.Add(0);
+  histogram.Add(1);
+
+  ASSERT_LE(fabs(histogram.Percentile(50.0) - 0.5), kIota);
+}
+
 TEST_F(HistogramTest, MergeHistogram) {
   HistogramImpl histogram;
   HistogramImpl other;

From a126ec7d703af82af40cf1acf6255d8a3fa698fe Mon Sep 17 00:00:00 2001
From: Andrew Kryczka <andrewkr@fb.com>
Date: Thu, 31 Aug 2017 17:23:28 -0700
Subject: [PATCH 2/2] improve test case comment

---
 monitoring/histogram_test.cc | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/monitoring/histogram_test.cc b/monitoring/histogram_test.cc
index 950e6c80e76..df58822fc21 100644
--- a/monitoring/histogram_test.cc
+++ b/monitoring/histogram_test.cc
@@ -87,7 +87,11 @@ TEST_F(HistogramTest, BasicOperation) {
 
 TEST_F(HistogramTest, BoundaryValue) {
   HistogramImpl histogram;
-  // both should be in [0, 1], never (1, 2].
+  // - both should be in [0, 1] bucket because we place values on bucket
+  //   boundaries in the lower bucket.
+  // - all points are in [0, 1] bucket, so p50 will be 0.5
+  // - the test cannot be written with a single point since histogram won't
+  //   report percentiles lower than the min or greater than the max.
   histogram.Add(0);
   histogram.Add(1);