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127 lines
3.5 KiB
C++
127 lines
3.5 KiB
C++
/*
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* Copyright 2016 Facebook, Inc.
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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#pragma once
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#include <chrono>
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#include <cstdint>
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#include <type_traits>
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namespace folly { namespace detail {
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/*
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* Helper function to compute the average, given a specified input type and
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* return type.
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*/
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// If the input is long double, divide using long double to avoid losing
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// precision.
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template <typename ReturnType>
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ReturnType avgHelper(long double sum, uint64_t count) {
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if (count == 0) { return ReturnType(0); }
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const long double countf = count;
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return static_cast<ReturnType>(sum / countf);
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}
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// In all other cases divide using double precision.
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// This should be relatively fast, and accurate enough for most use cases.
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template <typename ReturnType, typename ValueType>
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typename std::enable_if<!std::is_same<typename std::remove_cv<ValueType>::type,
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long double>::value,
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ReturnType>::type
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avgHelper(ValueType sum, uint64_t count) {
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if (count == 0) { return ReturnType(0); }
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const double sumf = sum;
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const double countf = count;
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return static_cast<ReturnType>(sumf / countf);
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}
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/*
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* Helper function to compute the rate per Interval,
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* given the specified count recorded over the elapsed time period.
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*/
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template <
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typename ReturnType = double,
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typename Duration = std::chrono::seconds,
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typename Interval = Duration>
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ReturnType rateHelper(ReturnType count, Duration elapsed) {
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if (elapsed == Duration(0)) {
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return 0;
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}
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// Use std::chrono::duration_cast to convert between the native
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// duration and the desired interval. However, convert the rates,
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// rather than just converting the elapsed duration. Converting the
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// elapsed time first may collapse it down to 0 if the elapsed interval
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// is less than the desired interval, which will incorrectly result in
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// an infinite rate.
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typedef std::chrono::duration<
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ReturnType,
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std::ratio<Duration::period::den, Duration::period::num>>
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NativeRate;
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typedef std::chrono::duration<
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ReturnType, std::ratio<Interval::period::den,
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Interval::period::num>> DesiredRate;
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NativeRate native(count / elapsed.count());
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DesiredRate desired = std::chrono::duration_cast<DesiredRate>(native);
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return desired.count();
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}
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template<typename T>
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struct Bucket {
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public:
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typedef T ValueType;
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Bucket()
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: sum(ValueType()),
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count(0) {}
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void clear() {
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sum = ValueType();
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count = 0;
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}
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void add(const ValueType& s, uint64_t c) {
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// TODO: It would be nice to handle overflow here.
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sum += s;
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count += c;
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}
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Bucket& operator+=(const Bucket& o) {
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add(o.sum, o.count);
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return *this;
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}
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Bucket& operator-=(const Bucket& o) {
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// TODO: It would be nice to handle overflow here.
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sum -= o.sum;
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count -= o.count;
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return *this;
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}
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template <typename ReturnType>
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ReturnType avg() const {
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return avgHelper<ReturnType>(sum, count);
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}
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ValueType sum;
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uint64_t count;
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};
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}} // folly::detail
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