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// Copyright Yahoo. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
#pragma once
#include "field_length_info.h"
#include <atomic>
#include <algorithm>
#include <cstdint>
namespace search::index {
/**
* Class used to calculate average field length, with a bias towards
* the latest field lengths when max_num_samples samples have been reached.
*/
class FieldLengthCalculator {
std::atomic<double> _average_field_length;
std::atomic<uint32_t> _num_samples; // Capped by _max_num_samples
uint32_t _max_num_samples;
public:
FieldLengthCalculator()
: FieldLengthCalculator(0.0, 0)
{
}
FieldLengthCalculator(double average_field_length, uint32_t num_samples, uint32_t max_num_samples = 100000)
: _average_field_length(average_field_length),
_num_samples(std::min(num_samples, max_num_samples)),
_max_num_samples(max_num_samples)
{
}
FieldLengthCalculator(const FieldLengthInfo& info, uint32_t max_num_samples = 100000)
: _average_field_length(info.get_average_field_length()),
_num_samples(std::min(info.get_num_samples(), max_num_samples)),
_max_num_samples(max_num_samples)
{
}
double get_average_field_length() const { return _average_field_length.load(std::memory_order_relaxed); }
uint32_t get_num_samples() const { return _num_samples.load(std::memory_order_relaxed); }
uint32_t get_max_num_samples() const { return _max_num_samples; }
FieldLengthInfo get_info() const {
return FieldLengthInfo(get_average_field_length(), get_num_samples());
}
void add_field_length(uint32_t field_length) {
auto num_samples = get_num_samples();
if (num_samples < _max_num_samples) {
++num_samples;
_num_samples.store(num_samples, std::memory_order_relaxed);
}
_average_field_length.store((_average_field_length.load(std::memory_order_relaxed) * (num_samples - 1) + field_length) / num_samples, std::memory_order_relaxed);
}
};
}
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