114 lines
2.4 KiB
C++
114 lines
2.4 KiB
C++
// SPDX-License-Identifier: BSD-2-Clause
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// author: Max Kellermann <max.kellermann@gmail.com>
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#pragma once
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#include "HugeAllocator.hxx"
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#include <cassert>
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#include <map>
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/**
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* Helper class for #SparseBuffer which describes which portions of
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* the buffer have "known" data.
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*/
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class SparseMap {
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using size_type = std::size_t;
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/**
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* Key is start offset, value is end offset.
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*/
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using Map = std::map<size_type, size_type>;
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using Iterator = typename Map::iterator;
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Map map;
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public:
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explicit SparseMap(size_type size) noexcept
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:map{{size, size}} {
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assert(size > 0);
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}
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size_type size() const noexcept {
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return GetEndOffset();
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}
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struct CheckResult {
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size_type undefined_size;
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size_type defined_size;
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};
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/**
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* Check and classify the given offset. Returns a structure
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* which tells you how much data is undefined, and how much
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* data follows which is defined.
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*/
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CheckResult Check(size_type offset) const noexcept;
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/**
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* Commit a write: mark the given range in the buffer as
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* "defined".
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*/
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void Commit(size_type start_offset, size_type end_offset) noexcept;
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private:
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size_type GetEndOffset() const noexcept {
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return std::prev(map.end())->second;
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}
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Iterator CheckCollapsePrevious(Iterator i) noexcept;
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Iterator CheckCollapseNext(Iterator i) noexcept;
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};
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/**
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* A buffer which caches the contents of a "huge" array, and remembers
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* which chunks are available.
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*/
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template<typename T>
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class SparseBuffer {
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using Buffer = HugeArray<T>;
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using size_type = typename Buffer::size_type;
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Buffer buffer;
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SparseMap map;
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public:
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explicit SparseBuffer(size_type size)
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:buffer(size), map(size) {
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buffer.ForkCow(false);
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}
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size_type size() const noexcept {
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return map.size();
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}
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void SetName(const char *name) noexcept {
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buffer.SetName(name);
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}
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struct ReadResult {
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size_type undefined_size;
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std::span<const T> defined_buffer;
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constexpr bool HasData() const noexcept {
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return undefined_size == 0 &&
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!defined_buffer.empty();
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}
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};
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ReadResult Read(size_type offset) const noexcept {
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auto c = map.Check(offset);
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return {c.undefined_size, {&buffer.front() + offset + c.undefined_size, c.defined_size}};
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}
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std::span<T> Write(size_type offset) noexcept {
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auto c = map.Check(offset);
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return {&buffer.front() + offset, c.undefined_size};
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}
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void Commit(size_type start_offset, size_type end_offset) noexcept {
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map.Commit(start_offset, end_offset);
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}
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};
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