Fix the calculation of the histogram buckets and writing to the tensor in summary_db_writer

tensorflow/contrib/tensorboard/db/summary_db_writer.cc

@@ -1182,14 +1182,20 @@ class SummaryDbWriter : public SummaryWriterInterface {
     // See tensorboard/plugins/histogram/summary.py and data_compat.py
     Tensor t{DT_DOUBLE, {k, 3}};
     auto data = t.flat<double>();
-    for (int i = 0; i < k; ++i) {
-      double left_edge = ((i - 1 >= 0) ? histo.bucket_limit(i - 1)
-                                       : std::numeric_limits<double>::min());
-      double right_edge = ((i + 1 < k) ? histo.bucket_limit(i + 1)
-                                       : std::numeric_limits<double>::max());
-      data(i + 0) = left_edge;
-      data(i + 1) = right_edge;
-      data(i + 2) = histo.bucket(i);
+    for (int i = 0, j = 0; i < k; ++i) {
+      // TODO(nickfelt): reconcile with TensorBoard's data_compat.py
+      // From summary.proto
+      // Parallel arrays encoding the bucket boundaries and the bucket values.
+      // bucket(i) is the count for the bucket i.  The range for
+      // a bucket is:
+      //   i == 0:  -DBL_MAX .. bucket_limit(0)
+      //   i != 0:  bucket_limit(i-1) .. bucket_limit(i)
+      double left_edge = (i == 0) ? std::numeric_limits<double>::min()
+                                  : histo.bucket_limit(i - 1);
+
+      data(j++) = left_edge;
+      data(j++) = histo.bucket_limit(i);
+      data(j++) = histo.bucket(i);
     }
     int64 tag_id;
     PatchPluginName(s->mutable_metadata(), kHistogramPluginName);

tensorflow/contrib/tensorboard/db/summary_db_writer_test.cc

@@ -100,6 +100,56 @@ class SummaryDbWriterTest : public ::testing::Test {
   SummaryWriterInterface* writer_ = nullptr;
 };
 
+TEST_F(SummaryDbWriterTest, WriteHistogram_VerifyTensorValues) {
+  TF_ASSERT_OK(CreateSummaryDbWriter(db_, "histtest", "test1", "user1", &env_,
+                                     &writer_));
+  int step = 0;
+  std::unique_ptr<Event> e{new Event};
+  e->set_step(step);
+  e->set_wall_time(123);
+  Summary::Value* s = e->mutable_summary()->add_value();
+  s->set_tag("normal/myhisto");
+
+  double dummy_value = 10.123;
+  HistogramProto* proto = s->mutable_histo();
+  proto->Clear();
+  proto->set_min(dummy_value);
+  proto->set_max(dummy_value);
+  proto->set_num(dummy_value);
+  proto->set_sum(dummy_value);
+  proto->set_sum_squares(dummy_value);
+
+  int size = 3;
+  double bucket_limits[] = {-30.5, -10.5, -5.5};
+  double bucket[] = {-10, 10, 20};
+  for (int i = 0; i < size; i++) {
+    proto->add_bucket_limit(bucket_limits[i]);
+    proto->add_bucket(bucket[i]);
+  }
+  TF_ASSERT_OK(writer_->WriteEvent(std::move(e)));
+  TF_ASSERT_OK(writer_->Flush());
+  writer_->Unref();
+  writer_ = nullptr;
+
+  // TODO(nickfelt): implement QueryTensor() to encapsulate this
+  // Verify the data
+  string result = QueryString("SELECT data FROM Tensors");
+  const double* val = reinterpret_cast<const double*>(result.data());
+  double histarray[] = {std::numeric_limits<double>::min(),
+                        -30.5,
+                        -10,
+                        -30.5,
+                        -10.5,
+                        10,
+                        -10.5,
+                        -5.5,
+                        20};
+  int histarray_size = 9;
+  for (int i = 0; i < histarray_size; i++) {
+    EXPECT_EQ(histarray[i], val[i]);
+  }
+}
+
 TEST_F(SummaryDbWriterTest, NothingWritten_NoRowsCreated) {
   TF_ASSERT_OK(CreateSummaryDbWriter(db_, "mad-science", "train", "jart", &env_,
                                      &writer_));