EXPECT_TRUE(statistics.has_value());
  EXPECT_EQ(statistics.value().histogram_statistics().lower_bound(), 0.f);
  EXPECT_EQ(statistics.value().histogram_statistics().bin_width(), 2.f);
  // Trailing zeros should be removed.
  EXPECT_THAT(statistics.value().histogram_statistics().hist_freq(),
              ElementsAre(1, 0, 3, 5, 7, 6, 5));
}

  const CalibrationStatistics& stats = statistics_map.statistics().at("1");
  ASSERT_TRUE(stats.has_histogram_statistics());
  EXPECT_FLOAT_EQ(stats.histogram_statistics().bin_width(), 0.5f);
  EXPECT_FLOAT_EQ(stats.histogram_statistics().lower_bound(), 1.f);
  EXPECT_THAT(stats.histogram_statistics().hist_freq(),
              ElementsAre(1, 4, 6, 7, 3, 2, 1));
}

TEST_F(CalibrationStatisticsSaverTest, MultipleStats) {

          ),
      },
  )
  def test_histogram_calibration_methods(self, calibration_options):
    statistics = calib_stats_pb2.CalibrationStatistics()
    statistics.histogram_statistics.lower_bound = 0.0
    statistics.histogram_statistics.bin_width = 1.0

    hist_freq = np.zeros(501, dtype=np.int32)

    # Advanced calibration methods that use histograms detect outliers, so they

    // bins[i + 1] = lower_bound + bin_width * (i + 1)
    repeated float hist_freq = 3;
  }

  MinMaxStatistics min_max_statistics = 1;
  AverageMinMaxStatistics average_min_max_statistics = 2;
  HistogramStatistics histogram_statistics = 3;
}

message CalibrationStatisticsMap {
  // A map from the id of CustomAggregator op to its collected statistics.
  map<string, CalibrationStatistics> statistics = 1;

  def __init__(
      self,
      statistics: calib_stats_pb2.CalibrationStatistics,
      calib_opts: stablehlo_quant_config_pb2.CalibrationOptions,
  ):
    """Builds histogram using statistics.histogram_statistics.

    lower_bound                                    hist_mid
         v                                            v
         |=========|=========|=========|=========|=========|
                    bin width

  }
}

std::optional<CalibrationStatistics>
CalibrationStatisticsCollectorHistogram::GetStatistics() const {
  if (hist_freq_.empty()) return std::nullopt;

  CalibrationStatistics::HistogramStatistics hist_stats;

  // Skip trailing zeros in the histogram.
  int32_t real_size = hist_freq_.size();
  for (; real_size > 0; --real_size) {
    if (hist_freq_[real_size - 1] != 0) break;
  }