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// Copyright 2012 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#include "base/metrics/bucket_ranges.h"
#include <algorithm>
#include <cmath>
#include "base/containers/span.h"
#include "base/metrics/crc32.h"
namespace base {
namespace {
constexpr bool is_sorted_and_unique(
base::span<const HistogramBase::Sample32> c) {
// Return true if we cannot find any adjacent pair {a, b} where a >= b.
return std::adjacent_find(c.begin(), c.end(),
std::greater_equal<HistogramBase::Sample32>()) ==
c.end();
}
} // namespace
BucketRanges::BucketRanges(size_t num_ranges)
: ranges_(num_ranges, 0), checksum_(0) {}
BucketRanges::BucketRanges(base::span<const HistogramBase::Sample32> data)
: ranges_(data.begin(), data.end()), checksum_(0) {
// Because the range values must be in sorted order, it suffices to only
// validate that the first one is non-negative.
if (!ranges_.empty() && ranges_[0] >= 0 && is_sorted_and_unique(ranges_)) {
ResetChecksum();
} else {
ranges_.clear();
}
}
BucketRanges::~BucketRanges() = default;
uint32_t BucketRanges::CalculateChecksum() const {
// Crc of empty ranges_ happens to be 0. This early exit prevents trying to
// take the address of ranges_[0] which will fail for an empty vector even
// if that address is never used.
const size_t ranges_size = ranges_.size();
if (ranges_size == 0) {
return 0;
}
// Checksum is seeded with the ranges "size".
return Crc32(static_cast<uint32_t>(ranges_size), base::as_byte_span(ranges_));
}
bool BucketRanges::HasValidChecksum() const {
return CalculateChecksum() == checksum_;
}
void BucketRanges::ResetChecksum() {
checksum_ = CalculateChecksum();
}
bool BucketRanges::Equals(const BucketRanges* other) const {
if (checksum_ != other->checksum_) {
return false;
}
if (ranges_.size() != other->ranges_.size()) {
return false;
}
for (size_t index = 0; index < ranges_.size(); ++index) {
if (ranges_[index] != other->ranges_[index]) {
return false;
}
}
return true;
}
} // namespace base
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