forked from LeenkxTeam/Kmake
59 lines
2.2 KiB
C++
59 lines
2.2 KiB
C++
// Copyright 2020 The Chromium Authors
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// Use of this source code is governed by a BSD-style license that can be
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// found in the LICENSE file.
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#ifndef CRDTP_FIND_BY_FIRST_H_
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#define CRDTP_FIND_BY_FIRST_H_
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#include <algorithm>
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#include <cstdint>
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#include <memory>
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#include <vector>
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#include "export.h"
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#include "span.h"
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namespace crdtp {
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// =============================================================================
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// FindByFirst - Retrieval from a sorted vector that's keyed by span<uint8_t>.
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// =============================================================================
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// Given a vector of pairs sorted by the first element of each pair, find
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// the corresponding value given a key to be compared to the first element.
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// Together with std::inplace_merge and pre-sorting or std::sort, this can
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// be used to implement a minimalistic equivalent of Chromium's flat_map.
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// In this variant, the template parameter |T| is a value type and a
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// |default_value| is provided.
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template <typename T>
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T FindByFirst(const std::vector<std::pair<span<uint8_t>, T>>& sorted_by_first,
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span<uint8_t> key,
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T default_value) {
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auto it = std::lower_bound(
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sorted_by_first.begin(), sorted_by_first.end(), key,
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[](const std::pair<span<uint8_t>, T>& left, span<uint8_t> right) {
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return SpanLessThan(left.first, right);
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});
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return (it != sorted_by_first.end() && SpanEquals(it->first, key))
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? it->second
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: default_value;
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}
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// In this variant, the template parameter |T| is a class or struct that's
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// instantiated in std::unique_ptr, and we return either a T* or a nullptr.
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template <typename T>
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T* FindByFirst(const std::vector<std::pair<span<uint8_t>, std::unique_ptr<T>>>&
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sorted_by_first,
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span<uint8_t> key) {
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auto it = std::lower_bound(
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sorted_by_first.begin(), sorted_by_first.end(), key,
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[](const std::pair<span<uint8_t>, std::unique_ptr<T>>& left,
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span<uint8_t> right) { return SpanLessThan(left.first, right); });
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return (it != sorted_by_first.end() && SpanEquals(it->first, key))
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? it->second.get()
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: nullptr;
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}
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} // namespace crdtp
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#endif // CRDTP_FIND_BY_FIRST_H_
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