[yosys.git] / kernel / hashlib.h

// This is free and unencumbered software released into the public domain.
//
// Anyone is free to copy, modify, publish, use, compile, sell, or
// distribute this software, either in source code form or as a compiled
// binary, for any purpose, commercial or non-commercial, and by any
// means.

// -------------------------------------------------------
// Written by Clifford Wolf <clifford@clifford.at> in 2014
// -------------------------------------------------------

#ifndef HASHLIB_H
#define HASHLIB_H

#include <stdexcept>
#include <algorithm>
#include <string>
#include <vector>

namespace hashlib {

const int hashtable_size_trigger = 2;
const int hashtable_size_factor = 3;

// The XOR version of DJB2
inline unsigned int mkhash(unsigned int a, unsigned int b) {
        return ((a << 5) + a) ^ b;
}

// traditionally 5381 is used as starting value for the djb2 hash
const unsigned int mkhash_init = 5381;

// The ADD version of DJB2
// (use this version for cache locality in b)
inline unsigned int mkhash_add(unsigned int a, unsigned int b) {
        return ((a << 5) + a) + b;
}

inline unsigned int mkhash_xorshift(unsigned int a) {
        if (sizeof(a) == 4) {
                a ^= a << 13;
                a ^= a >> 17;
                a ^= a << 5;
        } else if (sizeof(a) == 8) {
                a ^= a << 13;
                a ^= a >> 7;
                a ^= a << 17;
        } else
                throw std::runtime_error("mkhash_xorshift() only implemented for 32 bit and 64 bit ints");
        return a;
}

template<typename T> struct hash_ops {
        static inline bool cmp(const T &a, const T &b) {
                return a == b;
        }
        static inline unsigned int hash(const T &a) {
                return a.hash();
        }
};

struct hash_int_ops {
        template<typename T>
        static inline bool cmp(T a, T b) {
                return a == b;
        }
};

template<> struct hash_ops<int32_t> : hash_int_ops
{
        static inline unsigned int hash(int32_t a) {
                return a;
        }
};
template<> struct hash_ops<int64_t> : hash_int_ops
{
        static inline unsigned int hash(int64_t a) {
                return mkhash((unsigned int)(a), (unsigned int)(a >> 32));
        }
};

template<> struct hash_ops<std::string> {
        static inline bool cmp(const std::string &a, const std::string &b) {
                return a == b;
        }
        static inline unsigned int hash(const std::string &a) {
                unsigned int v = 0;
                for (auto c : a)
                        v = mkhash(v, c);
                return v;
        }
};

template<typename P, typename Q> struct hash_ops<std::pair<P, Q>> {
        static inline bool cmp(std::pair<P, Q> a, std::pair<P, Q> b) {
                return a == b;
        }
        static inline unsigned int hash(std::pair<P, Q> a) {
                return mkhash(hash_ops<P>::hash(a.first), hash_ops<Q>::hash(a.second));
        }
};

template<typename... T> struct hash_ops<std::tuple<T...>> {
        static inline bool cmp(std::tuple<T...> a, std::tuple<T...> b) {
                return a == b;
        }
        template<size_t I = 0>
        static inline typename std::enable_if<I == sizeof...(T), unsigned int>::type hash(std::tuple<T...>) {
                return mkhash_init;
        }
        template<size_t I = 0>
        static inline typename std::enable_if<I != sizeof...(T), unsigned int>::type hash(std::tuple<T...> a) {
                typedef hash_ops<typename std::tuple_element<I, std::tuple<T...>>::type> element_ops_t;
                return mkhash(hash<I+1>(a), element_ops_t::hash(std::get<I>(a)));
        }
};

template<typename T> struct hash_ops<std::vector<T>> {
        static inline bool cmp(std::vector<T> a, std::vector<T> b) {
                return a == b;
        }
        static inline unsigned int hash(std::vector<T> a) {
                unsigned int h = mkhash_init;
                for (auto k : a)
                        h = mkhash(h, hash_ops<T>::hash(k));
                return h;
        }
};

struct hash_cstr_ops {
        static inline bool cmp(const char *a, const char *b) {
                for (int i = 0; a[i] || b[i]; i++)
                        if (a[i] != b[i])
                                return false;
                return true;
        }
        static inline unsigned int hash(const char *a) {
                unsigned int hash = mkhash_init;
                while (*a)
                        hash = mkhash(hash, *(a++));
                return hash;
        }
};

struct hash_ptr_ops {
        static inline bool cmp(const void *a, const void *b) {
                return a == b;
        }
        static inline unsigned int hash(const void *a) {
                return (uintptr_t)a;
        }
};

struct hash_obj_ops {
        static inline bool cmp(const void *a, const void *b) {
                return a == b;
        }
        template<typename T>
        static inline unsigned int hash(const T *a) {
                return a ? a->hash() : 0;
        }
};

template<typename T>
inline unsigned int mkhash(const T &v) {
        return hash_ops<T>().hash(v);
}

inline int hashtable_size(int min_size)
{
        static std::vector<int> zero_and_some_primes = {
                0, 23, 29, 37, 47, 59, 79, 101, 127, 163, 211, 269, 337, 431, 541, 677,
                853, 1069, 1361, 1709, 2137, 2677, 3347, 4201, 5261, 6577, 8231, 10289,
                12889, 16127, 20161, 25219, 31531, 39419, 49277, 61603, 77017, 96281,
                120371, 150473, 188107, 235159, 293957, 367453, 459317, 574157, 717697,
                897133, 1121423, 1401791, 1752239, 2190299, 2737937, 3422429, 4278037,
                5347553, 6684443, 8355563, 10444457, 13055587, 16319519, 20399411,
                25499291, 31874149, 39842687, 49803361, 62254207, 77817767, 97272239,
                121590311, 151987889, 189984863, 237481091, 296851369, 371064217
        };

        for (auto p : zero_and_some_primes)
                if (p >= min_size) return p;

        if (sizeof(int) == 4)
                throw std::length_error("hash table exceeded maximum size. use a ILP64 abi for larger tables.");

        for (auto p : zero_and_some_primes)
                if (100129 * p > min_size) return 100129 * p;

        throw std::length_error("hash table exceeded maximum size.");
}

template<typename K, typename T, typename OPS = hash_ops<K>> class dict;
template<typename K, int offset = 0, typename OPS = hash_ops<K>> class idict;
template<typename K, typename OPS = hash_ops<K>> class pool;
template<typename K, typename OPS = hash_ops<K>> class mfp;

template<typename K, typename T, typename OPS>
class dict
{
        struct entry_t
        {
                std::pair<K, T> udata;
                int next;

                entry_t() { }
                entry_t(const std::pair<K, T> &udata, int next) : udata(udata), next(next) { }
                entry_t(std::pair<K, T> &&udata, int next) : udata(std::move(udata)), next(next) { }
        };

        std::vector<int> hashtable;
        std::vector<entry_t> entries;
        OPS ops;

#ifdef NDEBUG
        static inline void do_assert(bool) { }
#else
        static inline void do_assert(bool cond) {
                if (!cond) throw std::runtime_error("dict<> assert failed.");
        }
#endif

        int do_hash(const K &key) const
        {
                unsigned int hash = 0;
                if (!hashtable.empty())
                        hash = ops.hash(key) % (unsigned int)(hashtable.size());
                return hash;
        }

        void do_rehash()
        {
                hashtable.clear();
                hashtable.resize(hashtable_size(entries.capacity() * hashtable_size_factor), -1);

                for (int i = 0; i < int(entries.size()); i++) {
                        do_assert(-1 <= entries[i].next && entries[i].next < int(entries.size()));
                        int hash = do_hash(entries[i].udata.first);
                        entries[i].next = hashtable[hash];
                        hashtable[hash] = i;
                }
        }

        int do_erase(int index, int hash)
        {
                do_assert(index < int(entries.size()));
                if (hashtable.empty() || index < 0)
                        return 0;

                int k = hashtable[hash];
                do_assert(0 <= k && k < int(entries.size()));

                if (k == index) {
                        hashtable[hash] = entries[index].next;
                } else {
                        while (entries[k].next != index) {
                                k = entries[k].next;
                                do_assert(0 <= k && k < int(entries.size()));
                        }
                        entries[k].next = entries[index].next;
                }

                int back_idx = entries.size()-1;

                if (index != back_idx)
                {
                        int back_hash = do_hash(entries[back_idx].udata.first);

                        k = hashtable[back_hash];
                        do_assert(0 <= k && k < int(entries.size()));

                        if (k == back_idx) {
                                hashtable[back_hash] = index;
                        } else {
                                while (entries[k].next != back_idx) {
                                        k = entries[k].next;
                                        do_assert(0 <= k && k < int(entries.size()));
                                }
                                entries[k].next = index;
                        }

                        entries[index] = std::move(entries[back_idx]);
                }

                entries.pop_back();

                if (entries.empty())
                        hashtable.clear();

                return 1;
        }

        int do_lookup(const K &key, int &hash) const
        {
                if (hashtable.empty())
                        return -1;

                if (entries.size() * hashtable_size_trigger > hashtable.size()) {
                        ((dict*)this)->do_rehash();
                        hash = do_hash(key);
                }

                int index = hashtable[hash];

                while (index >= 0 && !ops.cmp(entries[index].udata.first, key)) {
                        index = entries[index].next;
                        do_assert(-1 <= index && index < int(entries.size()));
                }

                return index;
        }

        int do_insert(const K &key, int &hash)
        {
                if (hashtable.empty()) {
                        entries.push_back(entry_t(std::pair<K, T>(key, T()), -1));
                        do_rehash();
                        hash = do_hash(key);
                } else {
                        entries.push_back(entry_t(std::pair<K, T>(key, T()), hashtable[hash]));
                        hashtable[hash] = entries.size() - 1;
                }
                return entries.size() - 1;
        }

        int do_insert(const std::pair<K, T> &value, int &hash)
        {
                if (hashtable.empty()) {
                        entries.push_back(entry_t(value, -1));
                        do_rehash();
                        hash = do_hash(value.first);
                } else {
                        entries.push_back(entry_t(value, hashtable[hash]));
                        hashtable[hash] = entries.size() - 1;
                }
                return entries.size() - 1;
        }

public:
        class const_iterator : public std::iterator<std::forward_iterator_tag, std::pair<K, T>>
        {
                friend class dict;
        protected:
                const dict *ptr;
                int index;
                const_iterator(const dict *ptr, int index) : ptr(ptr), index(index) { }
        public:
                const_iterator() { }
                const_iterator operator++() { index--; return *this; }
                bool operator<(const const_iterator &other) const { return index > other.index; }
                bool operator==(const const_iterator &other) const { return index == other.index; }
                bool operator!=(const const_iterator &other) const { return index != other.index; }
                const std::pair<K, T> &operator*() const { return ptr->entries[index].udata; }
                const std::pair<K, T> *operator->() const { return &ptr->entries[index].udata; }
        };

        class iterator : public std::iterator<std::forward_iterator_tag, std::pair<K, T>>
        {
                friend class dict;
        protected:
                dict *ptr;
                int index;
                iterator(dict *ptr, int index) : ptr(ptr), index(index) { }
        public:
                iterator() { }
                iterator operator++() { index--; return *this; }
                bool operator<(const iterator &other) const { return index > other.index; }
                bool operator==(const iterator &other) const { return index == other.index; }
                bool operator!=(const iterator &other) const { return index != other.index; }
                std::pair<K, T> &operator*() { return ptr->entries[index].udata; }
                std::pair<K, T> *operator->() { return &ptr->entries[index].udata; }
                const std::pair<K, T> &operator*() const { return ptr->entries[index].udata; }
                const std::pair<K, T> *operator->() const { return &ptr->entries[index].udata; }
                operator const_iterator() const { return const_iterator(ptr, index); }
        };

        dict()
        {
        }

        dict(const dict &other)
        {
                entries = other.entries;
                do_rehash();
        }

        dict(dict &&other)
        {
                swap(other);
        }

        dict &operator=(const dict &other) {
                entries = other.entries;
                do_rehash();
                return *this;
        }

        dict &operator=(dict &&other) {
                clear();
                swap(other);
                return *this;
        }

        dict(const std::initializer_list<std::pair<K, T>> &list)
        {
                for (auto &it : list)
                        insert(it);
        }

        template<class InputIterator>
        dict(InputIterator first, InputIterator last)
        {
                insert(first, last);
        }

        template<class InputIterator>
        void insert(InputIterator first, InputIterator last)
        {
                for (; first != last; ++first)
                        insert(*first);
        }

        std::pair<iterator, bool> insert(const K &key)
        {
                int hash = do_hash(key);
                int i = do_lookup(key, hash);
                if (i >= 0)
                        return std::pair<iterator, bool>(iterator(this, i), false);
                i = do_insert(key, hash);
                return std::pair<iterator, bool>(iterator(this, i), true);
        }

        std::pair<iterator, bool> insert(const std::pair<K, T> &value)
        {
                int hash = do_hash(value.first);
                int i = do_lookup(value.first, hash);
                if (i >= 0)
                        return std::pair<iterator, bool>(iterator(this, i), false);
                i = do_insert(value, hash);
                return std::pair<iterator, bool>(iterator(this, i), true);
        }

        int erase(const K &key)
        {
                int hash = do_hash(key);
                int index = do_lookup(key, hash);
                return do_erase(index, hash);
        }

        iterator erase(iterator it)
        {
                int hash = do_hash(it->first);
                do_erase(it.index, hash);
                return ++it;
        }

        int count(const K &key) const
        {
                int hash = do_hash(key);
                int i = do_lookup(key, hash);
                return i < 0 ? 0 : 1;
        }

        int count(const K &key, const_iterator it) const
        {
                int hash = do_hash(key);
                int i = do_lookup(key, hash);
                return i < 0 || i > it.index ? 0 : 1;
        }

        iterator find(const K &key)
        {
                int hash = do_hash(key);
                int i = do_lookup(key, hash);
                if (i < 0)
                        return end();
                return iterator(this, i);
        }

        const_iterator find(const K &key) const
        {
                int hash = do_hash(key);
                int i = do_lookup(key, hash);
                if (i < 0)
                        return end();
                return const_iterator(this, i);
        }

        T& at(const K &key)
        {
                int hash = do_hash(key);
                int i = do_lookup(key, hash);
                if (i < 0)
                        throw std::out_of_range("dict::at()");
                return entries[i].udata.second;
        }

        const T& at(const K &key) const
        {
                int hash = do_hash(key);
                int i = do_lookup(key, hash);
                if (i < 0)
                        throw std::out_of_range("dict::at()");
                return entries[i].udata.second;
        }

        T at(const K &key, const T &defval) const
        {
                int hash = do_hash(key);
                int i = do_lookup(key, hash);
                if (i < 0)
                        return defval;
                return entries[i].udata.second;
        }

        T& operator[](const K &key)
        {
                int hash = do_hash(key);
                int i = do_lookup(key, hash);
                if (i < 0)
                        i = do_insert(std::pair<K, T>(key, T()), hash);
                return entries[i].udata.second;
        }

        template<typename Compare = std::less<K>>
        void sort(Compare comp = Compare())
        {
                std::sort(entries.begin(), entries.end(), [comp](const entry_t &a, const entry_t &b){ return comp(b.udata.first, a.udata.first); });
                do_rehash();
        }

        void swap(dict &other)
        {
                hashtable.swap(other.hashtable);
                entries.swap(other.entries);
        }

        bool operator==(const dict &other) const {
                if (size() != other.size())
                        return false;
                for (auto &it : entries) {
                        auto oit = other.find(it.udata.first);
                        if (oit == other.end() || !(oit->second == it.udata.second))
                                return false;
                }
                return true;
        }

        bool operator!=(const dict &other) const {
                return !operator==(other);
        }

        void reserve(size_t n) { entries.reserve(n); }
        size_t size() const { return entries.size(); }
        bool empty() const { return entries.empty(); }
        void clear() { hashtable.clear(); entries.clear(); }

        iterator begin() { return iterator(this, int(entries.size())-1); }
        iterator end() { return iterator(nullptr, -1); }

        const_iterator begin() const { return const_iterator(this, int(entries.size())-1); }
        const_iterator end() const { return const_iterator(nullptr, -1); }
};

template<typename K, typename OPS>
class pool
{
        template<typename, int, typename> friend class idict;

protected:
        struct entry_t
        {
                K udata;
                int next;

                entry_t() { }
                entry_t(const K &udata, int next) : udata(udata), next(next) { }
        };

        std::vector<int> hashtable;
        std::vector<entry_t> entries;
        OPS ops;

#ifdef NDEBUG
        static inline void do_assert(bool) { }
#else
        static inline void do_assert(bool cond) {
                if (!cond) throw std::runtime_error("pool<> assert failed.");
        }
#endif

        int do_hash(const K &key) const
        {
                unsigned int hash = 0;
                if (!hashtable.empty())
                        hash = ops.hash(key) % (unsigned int)(hashtable.size());
                return hash;
        }

        void do_rehash()
        {
                hashtable.clear();
                hashtable.resize(hashtable_size(entries.capacity() * hashtable_size_factor), -1);

                for (int i = 0; i < int(entries.size()); i++) {
                        do_assert(-1 <= entries[i].next && entries[i].next < int(entries.size()));
                        int hash = do_hash(entries[i].udata);
                        entries[i].next = hashtable[hash];
                        hashtable[hash] = i;
                }
        }

        int do_erase(int index, int hash)
        {
                do_assert(index < int(entries.size()));
                if (hashtable.empty() || index < 0)
                        return 0;

                int k = hashtable[hash];
                if (k == index) {
                        hashtable[hash] = entries[index].next;
                } else {
                        while (entries[k].next != index) {
                                k = entries[k].next;
                                do_assert(0 <= k && k < int(entries.size()));
                        }
                        entries[k].next = entries[index].next;
                }

                int back_idx = entries.size()-1;

                if (index != back_idx)
                {
                        int back_hash = do_hash(entries[back_idx].udata);

                        k = hashtable[back_hash];
                        if (k == back_idx) {
                                hashtable[back_hash] = index;
                        } else {
                                while (entries[k].next != back_idx) {
                                        k = entries[k].next;
                                        do_assert(0 <= k && k < int(entries.size()));
                                }
                                entries[k].next = index;
                        }

                        entries[index] = std::move(entries[back_idx]);
                }

                entries.pop_back();

                if (entries.empty())
                        hashtable.clear();

                return 1;
        }

        int do_lookup(const K &key, int &hash) const
        {
                if (hashtable.empty())
                        return -1;

                if (entries.size() * hashtable_size_trigger > hashtable.size()) {
                        ((pool*)this)->do_rehash();
                        hash = do_hash(key);
                }

                int index = hashtable[hash];

                while (index >= 0 && !ops.cmp(entries[index].udata, key)) {
                        index = entries[index].next;
                        do_assert(-1 <= index && index < int(entries.size()));
                }

                return index;
        }

        int do_insert(const K &value, int &hash)
        {
                if (hashtable.empty()) {
                        entries.push_back(entry_t(value, -1));
                        do_rehash();
                        hash = do_hash(value);
                } else {
                        entries.push_back(entry_t(value, hashtable[hash]));
                        hashtable[hash] = entries.size() - 1;
                }
                return entries.size() - 1;
        }

public:
        class const_iterator : public std::iterator<std::forward_iterator_tag, K>
        {
                friend class pool;
        protected:
                const pool *ptr;
                int index;
                const_iterator(const pool *ptr, int index) : ptr(ptr), index(index) { }
        public:
                const_iterator() { }
                const_iterator operator++() { index--; return *this; }
                bool operator==(const const_iterator &other) const { return index == other.index; }
                bool operator!=(const const_iterator &other) const { return index != other.index; }
                const K &operator*() const { return ptr->entries[index].udata; }
                const K *operator->() const { return &ptr->entries[index].udata; }
        };

        class iterator : public std::iterator<std::forward_iterator_tag, K>
        {
                friend class pool;
        protected:
                pool *ptr;
                int index;
                iterator(pool *ptr, int index) : ptr(ptr), index(index) { }
        public:
                iterator() { }
                iterator operator++() { index--; return *this; }
                bool operator==(const iterator &other) const { return index == other.index; }
                bool operator!=(const iterator &other) const { return index != other.index; }
                K &operator*() { return ptr->entries[index].udata; }
                K *operator->() { return &ptr->entries[index].udata; }
                const K &operator*() const { return ptr->entries[index].udata; }
                const K *operator->() const { return &ptr->entries[index].udata; }
                operator const_iterator() const { return const_iterator(ptr, index); }
        };

        pool()
        {
        }

        pool(const pool &other)
        {
                entries = other.entries;
                do_rehash();
        }

        pool(pool &&other)
        {
                swap(other);
        }

        pool &operator=(const pool &other) {
                entries = other.entries;
                do_rehash();
                return *this;
        }

        pool &operator=(pool &&other) {
                clear();
                swap(other);
                return *this;
        }

        pool(const std::initializer_list<K> &list)
        {
                for (auto &it : list)
                        insert(it);
        }

        template<class InputIterator>
        pool(InputIterator first, InputIterator last)
        {
                insert(first, last);
        }

        template<class InputIterator>
        void insert(InputIterator first, InputIterator last)
        {
                for (; first != last; ++first)
                        insert(*first);
        }

        std::pair<iterator, bool> insert(const K &value)
        {
                int hash = do_hash(value);
                int i = do_lookup(value, hash);
                if (i >= 0)
                        return std::pair<iterator, bool>(iterator(this, i), false);
                i = do_insert(value, hash);
                return std::pair<iterator, bool>(iterator(this, i), true);
        }

        int erase(const K &key)
        {
                int hash = do_hash(key);
                int index = do_lookup(key, hash);
                return do_erase(index, hash);
        }

        iterator erase(iterator it)
        {
                int hash = do_hash(*it);
                do_erase(it.index, hash);
                return ++it;
        }

        int count(const K &key) const
        {
                int hash = do_hash(key);
                int i = do_lookup(key, hash);
                return i < 0 ? 0 : 1;
        }

        int count(const K &key, const_iterator it) const
        {
                int hash = do_hash(key);
                int i = do_lookup(key, hash);
                return i < 0 || i > it.index ? 0 : 1;
        }

        iterator find(const K &key)
        {
                int hash = do_hash(key);
                int i = do_lookup(key, hash);
                if (i < 0)
                        return end();
                return iterator(this, i);
        }

        const_iterator find(const K &key) const
        {
                int hash = do_hash(key);
                int i = do_lookup(key, hash);
                if (i < 0)
                        return end();
                return const_iterator(this, i);
        }

        bool operator[](const K &key)
        {
                int hash = do_hash(key);
                int i = do_lookup(key, hash);
                return i >= 0;
        }

        template<typename Compare = std::less<K>>
        void sort(Compare comp = Compare())
        {
                std::sort(entries.begin(), entries.end(), [comp](const entry_t &a, const entry_t &b){ return comp(b.udata, a.udata); });
                do_rehash();
        }

        K pop()
        {
                iterator it = begin();
                K ret = *it;
                erase(it);
                return ret;
        }

        void swap(pool &other)
        {
                hashtable.swap(other.hashtable);
                entries.swap(other.entries);
        }

        bool operator==(const pool &other) const {
                if (size() != other.size())
                        return false;
                for (auto &it : entries)
                        if (!other.count(it.udata))
                                return false;
                return true;
        }

        bool operator!=(const pool &other) const {
                return !operator==(other);
        }

        void reserve(size_t n) { entries.reserve(n); }
        size_t size() const { return entries.size(); }
        bool empty() const { return entries.empty(); }
        void clear() { hashtable.clear(); entries.clear(); }

        iterator begin() { return iterator(this, int(entries.size())-1); }
        iterator end() { return iterator(nullptr, -1); }

        const_iterator begin() const { return const_iterator(this, int(entries.size())-1); }
        const_iterator end() const { return const_iterator(nullptr, -1); }
};

template<typename K, int offset, typename OPS>
class idict
{
        pool<K, OPS> database;

public:
        typedef typename pool<K, OPS>::const_iterator const_iterator;

        int operator()(const K &key)
        {
                int hash = database.do_hash(key);
                int i = database.do_lookup(key, hash);
                if (i < 0)
                        i = database.do_insert(key, hash);
                return i + offset;
        }

        int at(const K &key) const
        {
                int hash = database.do_hash(key);
                int i = database.do_lookup(key, hash);
                if (i < 0)
                        throw std::out_of_range("idict::at()");
                return i + offset;
        }

        int at(const K &key, int defval) const
        {
                int hash = database.do_hash(key);
                int i = database.do_lookup(key, hash);
                if (i < 0)
                        return defval;
                return i + offset;
        }

        int count(const K &key) const
        {
                int hash = database.do_hash(key);
                int i = database.do_lookup(key, hash);
                return i < 0 ? 0 : 1;
        }

        void expect(const K &key, int i)
        {
                int j = (*this)(key);
                if (i != j)
                        throw std::out_of_range("idict::expect()");
        }

        const K &operator[](int index) const
        {
                return database.entries.at(index - offset).udata;
        }

        void swap(idict &other)
        {
                database.swap(other.database);
        }

        void reserve(size_t n) { database.reserve(n); }
        size_t size() const { return database.size(); }
        bool empty() const { return database.empty(); }
        void clear() { database.clear(); }

        const_iterator begin() const { return database.begin(); }
        const_iterator end() const { return database.end(); }
};

template<typename K, typename OPS>
class mfp
{
        mutable idict<K, 0, OPS> database;
        mutable std::vector<int> parents;

public:
        typedef typename idict<K, 0, OPS>::const_iterator const_iterator;

        int operator()(const K &key) const
        {
                int i = database(key);
                parents.resize(database.size(), -1);
                return i;
        }

        const K &operator[](int index) const
        {
                return database[index];
        }

        int ifind(int i) const
        {
                int p = i, k = i;

                while (parents[p] != -1)
                        p = parents[p];

                while (k != p) {
                        int next_k = parents[k];
                        parents[k] = p;
                        k = next_k;
                }

                return p;
        }

        void imerge(int i, int j)
        {
                i = ifind(i);
                j = ifind(j);

                if (i != j)
                        parents[i] = j;
        }

        void ipromote(int i)
        {
                int k = i;

                while (k != -1) {
                        int next_k = parents[k];
                        parents[k] = i;
                        k = next_k;
                }

                parents[i] = -1;
        }

        int lookup(const K &a) const
        {
                return ifind((*this)(a));
        }

        const K &find(const K &a) const
        {
                int i = database.at(a, -1);
                if (i < 0)
                        return a;
                return (*this)[ifind(i)];
        }

        void merge(const K &a, const K &b)
        {
                imerge((*this)(a), (*this)(b));
        }

        void promote(const K &a)
        {
                int i = database.at(a, -1);
                if (i >= 0)
                        ipromote(i);
        }

        void swap(mfp &other)
        {
                database.swap(other.database);
                parents.swap(other.parents);
        }

        void reserve(size_t n) { database.reserve(n); }
        size_t size() const { return database.size(); }
        bool empty() const { return database.empty(); }
        void clear() { database.clear(); parents.clear(); }

        const_iterator begin() const { return database.begin(); }
        const_iterator end() const { return database.end(); }
};

} /* namespace hashlib */

#endif