From 420373475e9f8c4a2c3b570ee3c528090fa2ce49 Mon Sep 17 00:00:00 2001
From: Maxime Coste <mawww@kakoune.org>
Date: Mon, 6 Mar 2017 19:47:26 +0000
Subject: [PATCH] Introduce a custom HashMap implementation along with a quick
 benchmark

---
 src/commands.cc |   7 +-
 src/hash.hh     |   7 ++
 src/hash_map.cc | 156 +++++++++++++++++++++++++
 src/hash_map.hh | 299 ++++++++++++++++++++++++++++++++++++++++++++++++
 src/string.hh   |  11 ++
 5 files changed, 479 insertions(+), 1 deletion(-)
 create mode 100644 src/hash_map.cc
 create mode 100644 src/hash_map.hh

diff --git a/src/commands.cc b/src/commands.cc
index 4260c9ab..fd6b7552 100644
--- a/src/commands.cc
+++ b/src/commands.cc
@@ -12,6 +12,7 @@
 #include "event_manager.hh"
 #include "face_registry.hh"
 #include "file.hh"
+#include "hash_map.hh"
 #include "highlighter.hh"
 #include "highlighters.hh"
 #include "option_manager.hh"
@@ -1126,7 +1127,7 @@ const CommandDesc debug_cmd = {
     make_completer(
         [](const Context& context, CompletionFlags flags,
            const String& prefix, ByteCount cursor_pos) -> Completions {
-               auto c = {"info", "buffers", "options", "memory", "shared-strings"};
+               auto c = {"info", "buffers", "options", "memory", "shared-strings", "profile-hash-maps"};
                return { 0_byte, cursor_pos, complete(prefix, cursor_pos, c) };
     }),
     [](const ParametersParser& parser, Context& context, const ShellContext&)
@@ -1167,6 +1168,10 @@ const CommandDesc debug_cmd = {
         {
             StringRegistry::instance().debug_stats();
         }
+        else if (parser[0] == "profile-hash-maps")
+        {
+            profile_hash_maps();
+        }
         else
             throw runtime_error(format("unknown debug command '{}'", parser[0]));
     }
diff --git a/src/hash.hh b/src/hash.hh
index 896478f3..ddce1cff 100644
--- a/src/hash.hh
+++ b/src/hash.hh
@@ -58,6 +58,13 @@ struct Hash
     }
 };
 
+// Traits specifying if two types have compatible hashing, that is,
+// if lhs == rhs => hash_value(lhs) == hash_value(rhs)
+template<typename Lhs, typename Rhs>
+struct HashCompatible : std::false_type {};
+
+template<typename T> struct HashCompatible<T, T> : std::true_type {};
+
 }
 
 #endif // hash_hh_INCLUDED
diff --git a/src/hash_map.cc b/src/hash_map.cc
new file mode 100644
index 00000000..bc2d6ce2
--- /dev/null
+++ b/src/hash_map.cc
@@ -0,0 +1,156 @@
+#include "hash_map.hh"
+
+#include "clock.hh"
+#include "string.hh"
+#include "buffer_utils.hh"
+#include "unit_tests.hh"
+
+#include <random>
+
+namespace Kakoune
+{
+
+UnitTest test_hash_map{[] {
+    // Basic usage
+    {
+        HashMap<int, int> map;
+        map.insert({10, 1});
+        map.insert({20, 2});
+        kak_assert(map.find_index(0) == -1);
+        kak_assert(map.find_index(10) == 0);
+        kak_assert(map.find_index(20) == 1);
+        kak_assert(map[10] == 1);
+        kak_assert(map[20] == 2);
+        kak_assert(map[30] == 0);
+        map[30] = 3;
+        kak_assert(map.find_index(30) == 2);
+        map.remove(20);
+        kak_assert(map.find_index(30) == 1);
+        kak_assert(map.size() == 2);
+    }
+
+    // Multiple entries with the same key
+    {
+        HashMap<int, int> map;
+        map.insert({10, 1});
+        map.insert({10, 2});
+        kak_assert(map.find_index(10) == 0);
+        map.remove(10);
+        kak_assert(map.find_index(10) == 0);
+        map.remove(10);
+        kak_assert(map.find_index(10) == -1);
+        map.insert({20, 1});
+        map.insert({20, 2});
+        map.remove_all(20);
+        kak_assert(map.find_index(20) == -1);
+    }
+
+    // Check hash compatible support
+    {
+        HashMap<String, int> map;
+        map.insert({"test", 10});
+        kak_assert(map["test"_sv] == 10);
+        map.remove("test"_sv);
+    }
+
+    // make sure we get what we expect from the hash map
+    {
+        std::random_device dev;
+        std::default_random_engine re{dev()};
+        std::uniform_int_distribution<int> dist;
+
+        HashMap<int, int> map;
+        Vector<std::pair<int, int>> ref;
+
+        for (int i = 0; i < 100; ++i)
+        {
+            auto key = dist(re), value = dist(re);
+            ref.push_back({key, value});
+            map.insert({key, value});
+
+            std::random_shuffle(ref.begin(), ref.end());
+            for (auto& elem : ref)
+            {
+                auto it = map.find(elem.first);
+                kak_assert(it != map.end() and it->value == elem.second);
+            }
+        }
+    }
+}};
+
+struct HashStats
+{
+    size_t max_dist;
+    float mean_dist; 
+    float fill_rate;
+};
+
+template<MemoryDomain domain>
+HashStats HashIndex<domain>::compute_stats() const
+{
+    size_t count = 0;
+    size_t max_dist = 0;
+    size_t sum_dist = 0;
+    for (size_t slot = 0; slot < m_entries.size(); ++slot)
+    {
+        auto& entry = m_entries[slot];
+        if (entry.index == -1)
+            continue;
+        ++count;
+        auto dist = slot - compute_slot(entry.hash);
+        max_dist = std::max(max_dist, dist);
+        sum_dist += dist;
+    }
+
+    return { max_dist, (float)sum_dist / count, (float)count / m_entries.size() };
+}
+
+template<typename Key, typename Value, MemoryDomain domain>
+HashStats HashMap<Key, Value, domain>::compute_stats() const
+{
+    return m_index.compute_stats();
+}
+
+template<typename Map>
+void do_profile(size_t count, StringView type)
+{
+    std::random_device dev;
+    std::default_random_engine re{dev()};
+    std::uniform_int_distribution<size_t> dist{0, count};
+
+    Vector<size_t> vec;
+    for (size_t i = 0; i < count; ++i)
+        vec.push_back(i);
+    std::random_shuffle(vec.begin(), vec.end());
+
+    Map map;
+    auto start = Clock::now();
+
+    for (auto v : vec)
+        map.insert({v, dist(re)});
+    auto after_insert = Clock::now();
+
+    for (size_t i = 0; i < count; ++i)
+        ++map[dist(re)];
+    auto after_read = Clock::now();
+
+    for (size_t i = 0; i < count; ++i)
+        map.erase(dist(re));
+    auto after_remove = Clock::now();
+
+    write_to_debug_buffer(format("{} ({}) -- inserts: {}ms, reads: {}ms, remove: {}ms", type, count,
+                                 std::chrono::duration_cast<std::chrono::milliseconds>(after_insert - start).count(),
+                                 std::chrono::duration_cast<std::chrono::milliseconds>(after_read - after_insert).count(),
+                                 std::chrono::duration_cast<std::chrono::milliseconds>(after_remove - after_read).count()));
+}
+
+void profile_hash_maps()
+{
+    for (auto i : { 1000, 10000, 100000, 1000000, 10000000 })
+    {
+        do_profile<UnorderedMap<size_t, size_t>>(i, "UnorderedMap");
+        do_profile<HashMap<size_t, size_t>>(i, "   HashMap  ");
+    }
+}
+
+}
diff --git a/src/hash_map.hh b/src/hash_map.hh
new file mode 100644
index 00000000..6e4e1899
--- /dev/null
+++ b/src/hash_map.hh
@@ -0,0 +1,299 @@
+#ifndef hash_map_hh_INCLUDED
+#define hash_map_hh_INCLUDED
+
+#include "hash.hh"
+#include "memory.hh"
+#include "vector.hh"
+
+namespace Kakoune
+{
+
+class String;
+
+struct HashStats;
+
+template<MemoryDomain domain>
+struct HashIndex
+{
+    struct Entry
+    {
+        size_t hash;
+        int index;
+    };
+
+    void grow()
+    {
+        Vector<Entry, domain> old_entries = std::move(m_entries);
+        constexpr size_t init_size = 4;
+        m_entries.resize(old_entries.empty() ? init_size : old_entries.size() * 2, {0,-1});
+        for (auto& entry : old_entries)
+        {
+            if (entry.index >= 0)
+                add(entry.hash, entry.index);
+        }
+    }
+
+    void add(size_t hash, int index)
+    {
+        ++m_count;
+        if ((float)m_count / m_entries.size() > m_max_fill_rate)
+            grow();
+
+        Entry entry{hash, index};
+        while (true)
+        {
+            auto target_slot = compute_slot(entry.hash);
+            for (auto slot = target_slot; slot < m_entries.size(); ++slot)
+            {
+                if (m_entries[slot].index == -1)
+                {
+                    m_entries[slot] = entry;
+                    return;
+                }
+
+                // Robin hood hashing
+                auto candidate_slot = compute_slot(m_entries[slot].hash);
+                if (target_slot < candidate_slot)
+                {
+                    std::swap(m_entries[slot], entry);
+                    target_slot = candidate_slot;
+                }
+            }
+            // no free entries found, grow, try again
+            grow();
+        }
+    }
+
+    void remove(size_t hash, int index)
+    {
+        --m_count;
+        for (auto slot = compute_slot(hash); slot < m_entries.size(); ++slot)
+        {
+            kak_assert(m_entries[slot].index >= 0);
+            if (m_entries[slot].index == index)
+            {
+                m_entries[slot].index = -1;
+                // Recompact following entries
+                for (auto next = slot+1; next < m_entries.size(); ++next)
+                {
+                    if (m_entries[next].index == -1 or
+                        compute_slot(m_entries[next].hash) == next)
+                        break;
+                    kak_assert(compute_slot(m_entries[next].hash) < next);
+                    std::swap(m_entries[next-1], m_entries[next]);
+                }
+                break;
+            }
+        }
+    }
+
+    void ordered_fix_entries(int index)
+    {
+        // Fix entries index
+        for (auto& entry : m_entries)
+        {
+            if (entry.index >= index)
+                --entry.index;
+        }
+    }
+
+    void unordered_fix_entries(size_t hash, int old_index, int new_index)
+    {
+        for (auto slot = compute_slot(hash); slot < m_entries.size(); ++slot)
+        {
+            if (m_entries[slot].index == old_index)
+            {
+                m_entries[slot].index = new_index;
+                return;
+            }
+        }
+        kak_assert(false); // entry not found ?!
+    }
+
+    const Entry& operator[](size_t index) const { return m_entries[index]; }
+    size_t size() const { return m_entries.size(); }
+    size_t compute_slot(size_t hash) const
+    {
+        // We assume entries.size() is power of 2
+        return m_entries.empty() ? 0 : hash & (m_entries.size()-1);
+    }
+
+    void clear() { m_entries.clear(); }
+
+    HashStats compute_stats() const;
+
+private:
+    size_t m_count = 0;
+    float m_max_fill_rate = 0.5f;
+    Vector<Entry, domain> m_entries;
+};
+
+template<typename Key, typename Value, MemoryDomain domain = MemoryDomain::Undefined>
+struct HashMap
+{
+    struct Item
+    {
+        Key key;
+        Value value;
+    };
+
+    HashMap() = default;
+
+    HashMap(std::initializer_list<Item> val) : m_items{val}
+    {
+        for (int i = 0; i < m_items.size(); ++i)
+            m_index.add(hash_value(m_items[i].key), i);
+    }
+
+    Value& insert(Item item)
+    {
+        m_index.add(hash_value(item.key), (int)m_items.size());
+        m_items.push_back(std::move(item));
+        return m_items.back().value;
+    }
+
+    template<typename KeyType>
+    using EnableIfHashCompatible = typename std::enable_if<
+        HashCompatible<Key, typename std::decay<KeyType>::type>::value
+    >::type;
+
+    // For IdMap inteface compatibility, to remove
+    using Element = Item;
+    Value& append(Item item) { return insert(std::move(item)); }
+    static const String& get_id(const Element& e) { return e.key; }
+
+    template<typename KeyType, typename = EnableIfHashCompatible<KeyType>>
+    int find_index(const KeyType& key, size_t hash) const
+    {
+        for (auto slot = m_index.compute_slot(hash); slot < m_index.size(); ++slot)
+        {
+            auto& entry = m_index[slot];
+            if (entry.index == -1)
+                return -1;
+            if (entry.hash == hash and m_items[entry.index].key == key)
+                return entry.index;
+        }
+        return -1;
+    }
+
+    template<typename KeyType, typename = EnableIfHashCompatible<KeyType>>
+    int find_index(const KeyType& key) const { return find_index(key, hash_value(key)); }
+
+    template<typename KeyType, typename = EnableIfHashCompatible<KeyType>>
+    bool contains(const KeyType& key) const { return find_index(key) >= 0; }
+
+    template<typename KeyType, typename = EnableIfHashCompatible<KeyType>>
+    Value& operator[](KeyType&& key)
+    {
+        const auto hash = hash_value(key);
+        auto index = find_index(key, hash);
+        if (index >= 0)
+            return m_items[index].value;
+
+        m_index.add(hash, (int)m_items.size());
+        m_items.push_back({Key{std::forward<KeyType>(key)}, {}});
+        return m_items.back().value;
+    }
+
+    template<typename KeyType, typename = EnableIfHashCompatible<KeyType>>
+    void remove(const KeyType& key)
+    {
+        const auto hash = hash_value(key);
+        int index = find_index(key, hash);
+        if (index >= 0)
+        {
+            m_items.erase(m_items.begin() + index);
+            m_index.remove(hash, index);
+            m_index.ordered_fix_entries(index);
+        }
+    }
+
+    template<typename KeyType, typename = EnableIfHashCompatible<KeyType>>
+    void unordered_remove(const KeyType& key)
+    {
+        const auto hash = hash_value(key);
+        int index = find_index(key, hash);
+        if (index >= 0)
+        {
+            std::swap(m_items[index], m_items.back());
+            m_items.pop_back();
+            m_index.remove(hash, index);
+            if (index != m_items.size())
+                m_index.unordered_fix_entries(hash_value(m_items[index].key), m_items.size(), index);
+        }
+    }
+
+    void erase(const Key& key) { unordered_remove(key); }
+
+    template<typename KeyType, typename = EnableIfHashCompatible<KeyType>>
+    void remove_all(const KeyType& key)
+    {
+        const auto hash = hash_value(key);
+        for (int index = find_index(key, hash); index >= 0;
+             index = find_index(key, hash))
+        {
+            m_items.erase(m_items.begin() + index);
+            m_index.remove(hash, index);
+            m_index.ordered_fix_entries(index);
+        }
+    }
+
+    using iterator = typename Vector<Item, domain>::iterator;
+    iterator begin() { return m_items.begin(); }
+    iterator end() { return m_items.end(); }
+
+    using const_iterator = typename Vector<Item, domain>::const_iterator;
+    const_iterator begin() const { return m_items.begin(); }
+    const_iterator end() const { return m_items.end(); }
+
+    template<typename KeyType, typename = EnableIfHashCompatible<KeyType>>
+    iterator find(const KeyType& key)
+    {
+        auto index = find_index(key);
+        return index >= 0 ? begin() + index : end();
+    }
+
+    template<typename KeyType, typename = EnableIfHashCompatible<KeyType>>
+    const_iterator find(const KeyType& key) const
+    {
+        return const_cast<HashMap*>(this)->find(key);
+    }
+
+    void clear() { m_items.clear(); m_index.clear(); }
+
+    size_t size() const { return m_items.size(); }
+    bool empty() const { return m_items.empty(); }
+    void reserve(size_t size)
+    {
+        m_items.reserve(size); 
+        // TODO: Reserve in the index as well
+    }
+
+    // Equality is taking the order of insertion into account
+    template<MemoryDomain otherDomain>
+    bool operator==(const HashMap<Key, Value, otherDomain>& other) const
+    {
+        return size() == other.size() and
+            std::equal(begin(), end(), other.begin(),
+                       [](const Item& lhs, const Item& rhs) {
+                           return lhs.key == rhs.key and lhs.value == rhs.value;
+                       });
+    }
+
+    template<MemoryDomain otherDomain>
+    bool operator!=(const HashMap<Key, Value, otherDomain>& other) const
+    {
+        return not (*this == other);
+    }
+
+    HashStats compute_stats() const;
+private:
+    Vector<Item, domain> m_items;
+    HashIndex<domain> m_index;
+};
+
+void profile_hash_maps();
+
+}
+
+#endif // hash_map_hh_INCLUDED
diff --git a/src/string.hh b/src/string.hh
index 14e92bd7..6c0a467e 100644
--- a/src/string.hh
+++ b/src/string.hh
@@ -121,6 +121,8 @@ public:
     }
     String(const char* begin, const char* end) : m_data(begin, end-begin) {}
 
+    explicit String(StringView str);
+
     [[gnu::always_inline]]
     char* data() { return m_data.data(); }
 
@@ -254,6 +256,10 @@ private:
 
 static_assert(std::is_trivial<StringView>::value, "");
 
+template<> struct HashCompatible<String, StringView> : std::true_type {};
+
+inline String::String(StringView str) : String{str.begin(), str.length()} {}
+
 template<typename Type, typename CharType>
 inline StringView StringOps<Type, CharType>::substr(ByteCount from, ByteCount length) const
 {
@@ -319,6 +325,11 @@ inline String operator"" _str(const char* str, size_t)
     return String(str);
 }
 
+inline StringView operator"" _sv(const char* str, size_t)
+{
+    return StringView{str};
+}
+
 Vector<String> split(StringView str, char separator, char escape);
 Vector<StringView> split(StringView str, char separator);