Fix overflow when logging MaxInt32 to a sparse histogram.

base/metrics/sample_map.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/sample_map.h"
 
 #include "base/logging.h"
 #include "base/memory/ptr_util.h"
 #include "base/stl_util.h"
 
@@ skipping 12 matching lines @@
   typedef std::map<HistogramBase::Sample, HistogramBase::Count>
       SampleToCountMap;
 
   explicit SampleMapIterator(const SampleToCountMap& sample_counts);
   ~SampleMapIterator() override;
 
   // SampleCountIterator:
   bool Done() const override;
   void Next() override;
   void Get(HistogramBase::Sample* min,
-           HistogramBase::Sample* max,
+           int64_t* max,
            HistogramBase::Count* count) const override;
 
  private:
   void SkipEmptyBuckets();
 
   SampleToCountMap::const_iterator iter_;
   const SampleToCountMap::const_iterator end_;
 };
 
 SampleMapIterator::SampleMapIterator(const SampleToCountMap& sample_counts)
     : iter_(sample_counts.begin()),
       end_(sample_counts.end()) {
   SkipEmptyBuckets();
 }
 
 SampleMapIterator::~SampleMapIterator() {}
 
 bool SampleMapIterator::Done() const {
   return iter_ == end_;
 }
 
 void SampleMapIterator::Next() {
   DCHECK(!Done());
   ++iter_;
   SkipEmptyBuckets();
 }
 
-void SampleMapIterator::Get(Sample* min, Sample* max, Count* count) const {
+void SampleMapIterator::Get(Sample* min, int64_t* max, Count* count) const {
   DCHECK(!Done());
   if (min)
     *min = iter_->first;
   if (max)
-    *max = iter_->first + 1;
+    *max = static_cast<int64_t>(iter_->first) + 1;
   if (count)
     *count = iter_->second;
 }
 
 void SampleMapIterator::SkipEmptyBuckets() {
   while (!Done() && iter_->second == 0) {
     ++iter_;
   }
 }
 
@@ skipping 24 matching lines @@
   }
   return count;
 }
 
 std::unique_ptr<SampleCountIterator> SampleMap::Iterator() const {
   return WrapUnique(new SampleMapIterator(sample_counts_));
 }
 
 bool SampleMap::AddSubtractImpl(SampleCountIterator* iter, Operator op) {
   Sample min;
-  Sample max;
+  int64_t max;
   Count count;
   for (; !iter->Done(); iter->Next()) {
     iter->Get(&min, &max, &count);
-    if (min + 1 != max)
+    if (static_cast<int64_t>(min) + 1 != max)
       return false;  // SparseHistogram only supports bucket with size 1.
 
     sample_counts_[min] += (op == HistogramSamples::ADD) ? count : -count;
   }
   return true;
 }
 
 }  // namespace base