1// Copyright (c) 2012 The Chromium Authors. All rights reserved.
2// Use of this source code is governed by a BSD-style license that can be
3// found in the LICENSE file.
4//
5// BucketRanges stores the vector of ranges that delimit what samples are
6// tallied in the corresponding buckets of a histogram. Histograms that have
7// same ranges for all their corresponding buckets should share the same
8// BucketRanges object.
9//
10// E.g. A 5 buckets LinearHistogram with 1 as minimal value and 4 as maximal
11// value will need a BucketRanges with 6 ranges:
12// 0, 1, 2, 3, 4, INT_MAX
13//
14// TODO(kaiwang): Currently we keep all negative values in 0~1 bucket. Consider
15// changing 0 to INT_MIN.
16
17#ifndef BASE_METRICS_BUCKET_RANGES_H_
18#define BASE_METRICS_BUCKET_RANGES_H_
19
20#include <stddef.h>
21#include <stdint.h>
22
23#include <vector>
24
25#include <limits.h>
26
27#include "base/base_export.h"
28#include "base/macros.h"
29#include "base/metrics/histogram_base.h"
30
31namespace base {
32
33class BASE_EXPORT BucketRanges {
34 public:
35  typedef std::vector<HistogramBase::Sample> Ranges;
36
37  explicit BucketRanges(size_t num_ranges);
38  ~BucketRanges();
39
40  size_t size() const { return ranges_.size(); }
41  HistogramBase::Sample range(size_t i) const { return ranges_[i]; }
42  void set_range(size_t i, HistogramBase::Sample value);
43  uint32_t checksum() const { return checksum_; }
44  void set_checksum(uint32_t checksum) { checksum_ = checksum; }
45
46  // A bucket is defined by a consecutive pair of entries in |ranges|, so there
47  // is one fewer bucket than there are ranges.  For example, if |ranges| is
48  // [0, 1, 3, 7, INT_MAX], then the buckets in this histogram are
49  // [0, 1), [1, 3), [3, 7), and [7, INT_MAX).
50  size_t bucket_count() const { return ranges_.size() - 1; }
51
52  // Checksum methods to verify whether the ranges are corrupted (e.g. bad
53  // memory access).
54  uint32_t CalculateChecksum() const;
55  bool HasValidChecksum() const;
56  void ResetChecksum();
57
58  // Return true iff |other| object has same ranges_ as |this| object's ranges_.
59  bool Equals(const BucketRanges* other) const;
60
61 private:
62  // A monotonically increasing list of values which determine which bucket to
63  // put a sample into.  For each index, show the smallest sample that can be
64  // added to the corresponding bucket.
65  Ranges ranges_;
66
67  // Checksum for the conntents of ranges_.  Used to detect random over-writes
68  // of our data, and to quickly see if some other BucketRanges instance is
69  // possibly Equal() to this instance.
70  // TODO(kaiwang): Consider change this to uint64_t. Because we see a lot of
71  // noise on UMA dashboard.
72  uint32_t checksum_;
73
74  DISALLOW_COPY_AND_ASSIGN(BucketRanges);
75};
76
77//////////////////////////////////////////////////////////////////////////////
78// Expose only for test.
79BASE_EXPORT extern const uint32_t kCrcTable[256];
80
81}  // namespace base
82
83#endif  // BASE_METRICS_BUCKET_RANGES_H_
84