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198 行
4.3 KiB
198 行
4.3 KiB
#pragma once
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#include <cstddef>
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#include <array>
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#include <utility>
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#include <atomic>
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#include <new>
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#include <memory>
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#include <cassert>
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#include <optional>
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/**
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Pensé en un mundo sin memoria, sin tiempo; consideré la posibilidad de un lenguaje
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que ignorara los sustantivos, un lenguaje de verbos impersonales y de indeclinables
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epítetos. Así fueron muriendo los días y con los días los años, pero algo parecido
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a la felicidad ocurrió una mañana. Llovió, con lentitud poderosa.
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**/
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namespace mct20 {
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template<typename T>
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class accessor {
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public:
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accessor(const T* ptr, std::atomic<unsigned int>& incremented_ref)
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: pointer(ptr)
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, reference_cnt(incremented_ref)
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{
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assert(reference_cnt.load() != 0);
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}
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accessor(const accessor& a)
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: pointer(a.pointer)
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, reference_cnt(a.reference_cnt)
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{
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reference_cnt.fetch_add(1);
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}
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accessor(const accessor&& a)
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: pointer(a.pointer)
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, reference_cnt(a.reference_cnt)
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{
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reference_cnt.fetch_add(1);
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}
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operator const T&() {
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return *pointer;
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}
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~accessor() {
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reference_cnt.fetch_sub(1);
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}
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private:
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const T* pointer;
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std::atomic<unsigned int>& reference_cnt;
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};
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namespace _details_ {
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#ifdef __cpp_lib_hardware_interference_size
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constexpr size_t predictable_padding = std::hardware_constructive_interference_size;
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#else
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// Wild guess, may be suboptimal or plain wrong
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constexpr size_t predictable_padding = 128;
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#endif
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size_t rotl(size_t a, uint8_t b) {
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b%=sizeof(size_t)*8;
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return a << b | a >> (sizeof(size_t)*8 - b);
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}
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template<size_t against>
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constexpr size_t alignment =
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(against%predictable_padding!=0)*predictable_padding
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+ (against/predictable_padding)*predictable_padding;
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template<typename K, typename V>
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class bucket {
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public:
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bucket()
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: start{nullptr}
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{}
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void push(size_t hash, const K& key, const V& value) {
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auto t = new node{
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.contents = node_contents{
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.key{key},
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.ptr{new V{value}},
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.hash{hash},
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.references{1}
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}
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};
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t->contents.next.store(t);
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node* expect;
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do {
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expect = start.load();
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t->contents.next.store(expect);
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} while(
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!std::atomic_compare_exchange_strong(
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&start,
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&expect,
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t
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)
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);
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}
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std::optional<accessor<V>> get(const size_t hash, const K& key) {
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auto v = start.load();
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while(v) {
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if(v->contents.references.fetch_add(1)!=0)
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{
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if(v->contents.hash == hash) {
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if(v->contents.key == key) {
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return accessor<V>(
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v->contents.ptr,
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v->contents.references
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);
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} else {
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auto n = reinterpret_cast<node*>(v->contents.next.load());
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v->contents.references.fetch_sub(1);
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v = n;
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}
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} else {
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auto n = reinterpret_cast<node*>(v->contents.next.load());
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v->contents.references.fetch_sub(1);
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v = n;
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}
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}
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else
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{
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auto n = reinterpret_cast<node*>(v->contents.next.load());
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v->contents.references.fetch_sub(1);
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v = n;
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}
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}
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return std::nullopt;
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}
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struct node_contents{
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std::atomic<void*> next;
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const K key;
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const V* ptr;
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size_t hash;
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std::atomic<unsigned int> references;
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};
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using node = union {
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alignas(alignment<sizeof(node_contents)>) node_contents contents;
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};
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using node_ptr = std::atomic<node*>;
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node_ptr start;
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};
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}
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template<typename K, typename V, size_t bucket_count, typename hash = std::hash<K>>
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class lfhmap {
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using bucket = _details_::bucket<K, V>;
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public:
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std::optional<accessor<V>> get(const K& key) {
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auto l = hash{}(key);
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auto ret = buckets[l%bucket_count].get(l, key);
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if(ret) return ret;
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l = _details_::rotl(l, sizeof(size_t)*4);
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return buckets[l%bucket_count].get(l, key);
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}
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void set(const K& key, const V& value) {
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const auto l = hash{}(key);
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auto& ref = buckets[l%bucket_count];
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if(ref.start.load() == nullptr)
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{
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ref.push(l, key, value);
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return;
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}
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const auto l2 = _details_::rotl(l, sizeof(size_t)*4);
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auto& ref2 = buckets[l2%bucket_count];
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if(ref2.start.load() == nullptr)
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{
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ref2.push(l2, key, value);
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return;
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}
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if((l^l2)&1) {
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ref.push(l, key, value);
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} else {
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ref2.push(l2, key, value);
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}
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return;
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}
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lfhmap() {
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for(auto& a : buckets) {
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a.start = nullptr;
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}
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}
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private:
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std::array<bucket, bucket_count> buckets;
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};
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}
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