[histogram] Make histograms more resistant to overflows.

base/metrics/sparse_histogram_unittest.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "base/metrics/sparse_histogram.h"
 
 #include <memory>
 #include <string>
 
 #include "base/metrics/histogram_base.h"
@@ skipping 131 matching lines @@
 
   histogram->AddCount(1000000000, 15);
   histogram->AddCount(1010000000, 25);
   std::unique_ptr<HistogramSamples> snapshot2(histogram->SnapshotSamples());
   EXPECT_EQ(55, snapshot2->TotalCount());
   EXPECT_EQ(30, snapshot2->GetCount(1000000000));
   EXPECT_EQ(25, snapshot2->GetCount(1010000000));
   EXPECT_EQ(55250000000LL, snapshot2->sum());
 }
 
+// Make sure that counts returned by Histogram::SnapshotDelta do not overflow
+// even when a total count (returned by Histogram::SnapshotSample) does.
+TEST_P(SparseHistogramTest, AddCount_LargeCountsDontOverflow) {
+  std::unique_ptr<SparseHistogram> histogram(NewSparseHistogram("Sparse"));
+  std::unique_ptr<HistogramSamples> snapshot(histogram->SnapshotSamples());
+  EXPECT_EQ(0, snapshot->TotalCount());
+  EXPECT_EQ(0, snapshot->sum());
+
+  const int count = (1 << 30) - 1;
+
+  // Repeat N times to make sure that there is no internal value overflow.
+  for (int i = 0; i < 10; ++i) {
+    histogram->AddCount(42, count);
+    std::unique_ptr<HistogramSamples> samples = histogram->SnapshotDelta();
+    EXPECT_EQ(count, samples->TotalCount());
+    EXPECT_EQ(count, samples->GetCount(42));
+  }
+}
+
 TEST_P(SparseHistogramTest, MacroBasicTest) {
   UMA_HISTOGRAM_SPARSE_SLOWLY("Sparse", 100);
   UMA_HISTOGRAM_SPARSE_SLOWLY("Sparse", 200);
   UMA_HISTOGRAM_SPARSE_SLOWLY("Sparse", 100);
 
   StatisticsRecorder::Histograms histograms;
   StatisticsRecorder::GetHistograms(&histograms);
 
   ASSERT_EQ(1U, histograms.size());
   HistogramBase* sparse_histogram = histograms[0];
@@ skipping 196 matching lines @@
     EXPECT_EQ(1, count);
     EXPECT_EQ(cases[i].sample, min);
     EXPECT_EQ(cases[i].expected_max, max);
 
     it->Next();
     EXPECT_TRUE(it->Done());
   }
 }
 
 }  // namespace base