chromium/third_party/abseil-cpp/absl/container/internal/hashtable_debug.h

// Copyright 2018 The Abseil Authors.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//      https://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
//
// This library provides APIs to debug the probing behavior of hash tables.
//
// In general, the probing behavior is a black box for users and only the
// side effects can be measured in the form of performance differences.
// These APIs give a glimpse on the actual behavior of the probing algorithms in
// these hashtables given a specified hash function and a set of elements.
//
// The probe count distribution can be used to assess the quality of the hash
// function for that particular hash table. Note that a hash function that
// performs well in one hash table implementation does not necessarily performs
// well in a different one.
//
// This library supports std::unordered_{set,map}, dense_hash_{set,map} and
// absl::{flat,node,string}_hash_{set,map}.

#ifndef ABSL_CONTAINER_INTERNAL_HASHTABLE_DEBUG_H_
#define ABSL_CONTAINER_INTERNAL_HASHTABLE_DEBUG_H_

#include <cstddef>
#include <algorithm>
#include <type_traits>
#include <vector>

#include "absl/container/internal/hashtable_debug_hooks.h"

namespace absl {
ABSL_NAMESPACE_BEGIN
namespace container_internal {

// Returns the number of probes required to lookup `key`.  Returns 0 for a
// search with no collisions.  Higher values mean more hash collisions occurred;
// however, the exact meaning of this number varies according to the container
// type.
template <typename C>
size_t GetHashtableDebugNumProbes(
    const C& c, const typename C::key_type& key) { … }

// Gets a histogram of the number of probes for each elements in the container.
// The sum of all the values in the vector is equal to container.size().
template <typename C>
std::vector<size_t> GetHashtableDebugNumProbesHistogram(const C& container) { … }

struct HashtableDebugProbeSummary { … };

// Gets a summary of the probe count distribution for the elements in the
// container.
template <typename C>
HashtableDebugProbeSummary GetHashtableDebugProbeSummary(const C& container) { … }

// Returns the number of bytes requested from the allocator by the container
// and not freed.
template <typename C>
size_t AllocatedByteSize(const C& c) { … }

}  // namespace container_internal
ABSL_NAMESPACE_END
}  // namespace absl

#endif  // ABSL_CONTAINER_INTERNAL_HASHTABLE_DEBUG_H_