#ifndef DARTS_H_
#define DARTS_H_

#include <cstdio>
#include <exception>
#include <new>

#define DARTS_VERSION "0.32"

// DARTS_THROW() throws a <Darts::Exception> whose message starts with the
// file name and the line number. For example, DARTS_THROW("error message") at
// line 123 of "darts.h" throws a <Darts::Exception> which has a pointer to
// "darts.h:123: exception: error message". The message is available by using
// what() as well as that of <std::exception>.
#define DARTS_INT_TO_STR(value) #value
#define DARTS_LINE_TO_STR(line) DARTS_INT_TO_STR(line)
#define DARTS_LINE_STR DARTS_LINE_TO_STR(__LINE__)
#define DARTS_THROW(msg) throw Darts::Details::Exception(__FILE__ ":" DARTS_LINE_STR ": exception: " msg)

namespace Darts {

// The following namespace hides the internal types and classes.
namespace Details {

// This header assumes that <int> and <unsigned int> are 32-bit integer types.
//
// Darts-clone keeps values associated with keys. The type of the values is
// <value_type>. Note that the values must be positive integers because the
// most significant bit (MSB) of each value is used to represent whether the
// corresponding unit is a leaf or not. Also, the keys are represented by
// sequences of <char_type>s. <uchar_type> is the unsigned type of <char_type>.
typedef char char_type;
typedef unsigned char uchar_type;
typedef int value_type;

// The main structure of Darts-clone is an array of <DoubleArrayUnit>s, and the
// unit type is actually a wrapper of <id_type>.
typedef unsigned int id_type;

// <progress_func_type> is the type of callback functions for reporting the
// progress of building a dictionary. See also build() of <DoubleArray>.
// The 1st argument receives the progress value and the 2nd argument receives
// the maximum progress value. A usage example is to show the progress
// percentage, 100.0 * (the 1st argument) / (the 2nd argument).
typedef int (*progress_func_type)(std::size_t, std::size_t);

// <DoubleArrayUnit> is the type of double-array units and it is a wrapper of
// <id_type> in practice.
class DoubleArrayUnit {
public:
    DoubleArrayUnit() : unit_() {}

    // has_leaf() returns whether a leaf unit is immediately derived from the
    // unit (true) or not (false).
    bool has_leaf() const { return ((unit_ >> 8) & 1) == 1; }
    // value() returns the value stored in the unit, and thus value() is
    // available when and only when the unit is a leaf unit.
    value_type value() const { return static_cast<value_type>(unit_ & ((1U << 31) - 1)); }

    // label() returns the label associted with the unit. Note that a leaf unit
    // always returns an invalid label. For this feature, leaf unit's label()
    // returns an <id_type> that has the MSB of 1.
    id_type label() const { return unit_ & ((1U << 31) | 0xFF); }
    // offset() returns the offset from the unit to its derived units.
    id_type offset() const { return (unit_ >> 10) << ((unit_ & (1U << 9)) >> 6); }

private:
    id_type unit_;

    // Copyable.
};

// Darts-clone throws an <Exception> for memory allocation failure, invalid
// arguments or a too large offset. The last case means that there are too many
// keys in the given set of keys. Note that the `msg' of <Exception> must be a
// constant or static string because an <Exception> keeps only a pointer to
// that string.
class Exception : public std::exception {
public:
    explicit Exception(const char *msg = NULL) throw() : msg_(msg) {}
    Exception(const Exception &rhs) throw() : msg_(rhs.msg_) {}
    virtual ~Exception() throw() {}

    // <Exception> overrides what() of <std::exception>.
    virtual const char *what() const throw() { return (msg_ != NULL) ? msg_ : ""; }

private:
    const char *msg_;

    // Disallows operator=.
    Exception &operator=(const Exception &);
};

} // namespace Details

// <DoubleArrayImpl> is the interface of Darts-clone. Note that other
// classes should not be accessed from outside.
//
// <DoubleArrayImpl> has 4 template arguments but only the 3rd one is used as
// the type of values. Note that the given <T> is used only from outside, and
// the internal value type is not changed from <Darts::Details::value_type>.
// In build(), given values are casted from <T> to <Darts::Details::value_type>
// by using static_cast. On the other hand, values are casted from
// <Darts::Details::value_type> to <T> in searching dictionaries.
template <typename, typename, typename T, typename>
class DoubleArrayImpl {
public:
    // Even if this <value_type> is changed, the internal value type is still
    // <Darts::Details::value_type>. Other types, such as 64-bit integer types
    // and floating-point number types, should not be used.
    typedef T value_type;
    // A key is reprenseted by a sequence of <key_type>s. For example,
    // exactMatchSearch() takes a <const key_type *>.
    typedef Details::char_type key_type;
    // In searching dictionaries, the values associated with the matched keys are
    // stored into or returned as <result_type>s.
    typedef value_type result_type;

    // <result_pair_type> enables applications to get the lengths of the matched
    // keys in addition to the values.
    struct result_pair_type {
        value_type value;
        std::size_t length;
    };

    // The constructor initializes member variables with 0 and NULLs.
    DoubleArrayImpl() : size_(0), array_(NULL), buf_(NULL) {}
    // The destructor frees memory allocated for units and then initializes
    // member variables with 0 and NULLs.
    virtual ~DoubleArrayImpl() { clear(); }

    // <DoubleArrayImpl> has 2 kinds of set_result()s. The 1st set_result() is to
    // set a value to a <value_type>. The 2nd set_result() is to set a value and
    // a length to a <result_pair_type>. By using set_result()s, search methods
    // can return the 2 kinds of results in the same way.
    // Why the set_result()s are non-static? It is for compatibility.
    //
    // The 1st set_result() takes a length as the 3rd argument but it is not
    // used. If a compiler does a good job, codes for getting the length may be
    // removed.
    void set_result(value_type *result, value_type value, std::size_t) const { *result = value; }
    // The 2nd set_result() uses both `value' and `length'.
    void set_result(result_pair_type *result, value_type value, std::size_t length) const {
        result->value = value;
        result->length = length;
    }

    // set_array() calls clear() in order to free memory allocated to the old
    // array and then sets a new array. This function is useful to set a memory-
    // mapped array. Note that the array set by set_array() is not freed in
    // clear() and the destructor of <DoubleArrayImpl>.
    // set_array() can also set the size of the new array but the size is not
    // used in search methods. So it works well even if the 2nd argument is 0 or
    // omitted. Remember that size() and total_size() returns 0 in such a case.
    void set_array(const void *ptr, std::size_t size = 0) {
        clear();
        array_ = static_cast<const unit_type *>(ptr);
        size_ = size;
    }
    // array() returns a pointer to the array of units.
    const void *array() const { return array_; }

    // clear() frees memory allocated to units and then initializes member
    // variables with 0 and NULLs. Note that clear() does not free memory if the
    // array of units was set by set_array(). In such a case, `array_' is not
    // NULL and `buf_' is NULL.
    void clear() {
        size_ = 0;
        array_ = NULL;
        if (buf_ != NULL) {
            delete[] buf_;
            buf_ = NULL;
        }
    }

    // unit_size() returns the size of each unit. The size must be 4 bytes.
    std::size_t unit_size() const { return sizeof(unit_type); }
    // size() returns the number of units. It can be 0 if set_array() is used.
    std::size_t size() const { return size_; }
    // total_size() returns the number of bytes allocated to the array of units.
    // It can be 0 if set_array() is used.
    std::size_t total_size() const { return unit_size() * size(); }
    // nonzero_size() exists for compatibility. It always returns the number of
    // units because it takes long time to count the number of non-zero units.
    std::size_t nonzero_size() const { return size(); }

    // build() constructs a dictionary from given key-value pairs. If `lengths'
    // is NULL, `keys' is handled as an array of zero-terminated strings. If
    // `values' is NULL, the index in `keys' is associated with each key, i.e.
    // the ith key has (i - 1) as its value.
    // Note that the key-value pairs must be arranged in key order and the values
    // must not be negative. Also, if there are duplicate keys, only the first
    // pair will be stored in the resultant dictionary.
    // `progress_func' is a pointer to a callback function. If it is not NULL,
    // it will be called in build() so that the caller can check the progress of
    // dictionary construction. For details, please see the definition of
    // <Darts::Details::progress_func_type>.
    // The return value of build() is 0, and it indicates the success of the
    // operation. Otherwise, build() throws a <Darts::Exception>, which is a
    // derived class of <std::exception>.
    // build() uses another construction algorithm if `values' is not NULL. In
    // this case, Darts-clone uses a Directed Acyclic Word Graph (DAWG) instead
    // of a trie because a DAWG is likely to be more compact than a trie.
    int build(std::size_t num_keys,
              const key_type *const *keys,
              const std::size_t *lengths = NULL,
              const value_type *values = NULL,
              Details::progress_func_type progress_func = NULL);

    // open() reads an array of units from the specified file. And if it goes
    // well, the old array will be freed and replaced with the new array read
    // from the file. `offset' specifies the number of bytes to be skipped before
    // reading an array. `size' specifies the number of bytes to be read from the
    // file. If the `size' is 0, the whole file will be read.
    // open() returns 0 iff the operation succeeds. Otherwise, it returns a
    // non-zero value or throws a <Darts::Exception>. The exception is thrown
    // when and only when a memory allocation fails.
    int open(const char *file_name, const char *mode = "rb", std::size_t offset = 0, std::size_t size = 0);
    // save() writes the array of units into the specified file. `offset'
    // specifies the number of bytes to be skipped before writing the array.
    // open() returns 0 iff the operation succeeds. Otherwise, it returns a
    // non-zero value.
    int save(const char *file_name, const char *mode = "wb", std::size_t offset = 0) const;

    // The 1st exactMatchSearch() tests whether the given key exists or not, and
    // if it exists, its value and length are set to `result'. Otherwise, the
    // value and the length of `result' are set to -1 and 0 respectively.
    // Note that if `length' is 0, `key' is handled as a zero-terminated string.
    // `node_pos' specifies the start position of matching. This argument enables
    // the combination of exactMatchSearch() and traverse(). For example, if you
    // want to test "xyzA", "xyzBC", and "xyzDE", you can use traverse() to get
    // the node position corresponding to "xyz" and then you can use
    // exactMatchSearch() to test "A", "BC", and "DE" from that position.
    // Note that the length of `result' indicates the length from the `node_pos'.
    // In the above example, the lengths are { 1, 2, 2 }, not { 4, 5, 5 }.
    template <class U>
    void exactMatchSearch(const key_type *key, U &result, std::size_t length = 0, std::size_t node_pos = 0) const {
        result = exactMatchSearch<U>(key, length, node_pos);
    }
    // The 2nd exactMatchSearch() returns a result instead of updating the 2nd
    // argument. So, the following exactMatchSearch() has only 3 arguments.
    template <class U>
    inline U exactMatchSearch(const key_type *key, std::size_t length = 0, std::size_t node_pos = 0) const;

    // commonPrefixSearch() searches for keys which match a prefix of the given
    // string. If `length' is 0, `key' is handled as a zero-terminated string.
    // The values and the lengths of at most `max_num_results' matched keys are
    // stored in `results'. commonPrefixSearch() returns the number of matched
    // keys. Note that the return value can be larger than `max_num_results' if
    // there are more than `max_num_results' matches. If you want to get all the
    // results, allocate more spaces and call commonPrefixSearch() again.
    // `node_pos' works as well as in exactMatchSearch().
    template <class U>
    inline std::size_t
    commonPrefixSearch(const key_type *key, U *results, std::size_t max_num_results, std::size_t length = 0, std::size_t node_pos = 0) const;

    // In Darts-clone, a dictionary is a deterministic finite-state automaton
    // (DFA) and traverse() tests transitions on the DFA. The initial state is
    // `node_pos' and traverse() chooses transitions labeled key[key_pos],
    // key[key_pos + 1], ... in order. If there is not a transition labeled
    // key[key_pos + i], traverse() terminates the transitions at that state and
    // returns -2. Otherwise, traverse() ends without a termination and returns
    // -1 or a nonnegative value, -1 indicates that the final state was not an
    // accept state. When a nonnegative value is returned, it is the value
    // associated with the final accept state. That is, traverse() returns the
    // value associated with the given key if it exists. Note that traverse()
    // updates `node_pos' and `key_pos' after each transition.
    inline value_type traverse(const key_type *key, std::size_t &node_pos, std::size_t &key_pos, std::size_t length = 0) const;

private:
    typedef Details::uchar_type uchar_type;
    typedef Details::id_type id_type;
    typedef Details::DoubleArrayUnit unit_type;

    std::size_t size_;
    const unit_type *array_;
    unit_type *buf_;

    // Disallows copy and assignment.
    DoubleArrayImpl(const DoubleArrayImpl &);
    DoubleArrayImpl &operator=(const DoubleArrayImpl &);
};

// <DoubleArray> is the typical instance of <DoubleArrayImpl>. It uses <int>
// as the type of values and it is suitable for most cases.
typedef DoubleArrayImpl<void, void, int, void> DoubleArray;

// The interface section ends here. For using Darts-clone, there is no need
// to read the remaining section, which gives the implementation of
// Darts-clone.

//
// Member functions of DoubleArrayImpl (except build()).
//

template <typename A, typename B, typename T, typename C>
int DoubleArrayImpl<A, B, T, C>::open(const char *file_name, const char *mode, std::size_t offset, std::size_t size) {
#ifdef _MSC_VER
    std::FILE *file;
    if (::fopen_s(&file, file_name, mode) != 0) {
        return -1;
    }
#else
    std::FILE *file = std::fopen(file_name, mode);
    if (file == NULL) {
        return -1;
    }
#endif

    if (size == 0) {
        if (std::fseek(file, 0, SEEK_END) != 0) {
            std::fclose(file);
            return -1;
        }
        size = std::ftell(file) - offset;
    }

    size /= unit_size();
    if (size < 256 || (size & 0xFF) != 0) {
        std::fclose(file);
        return -1;
    }

    if (std::fseek(file, offset, SEEK_SET) != 0) {
        std::fclose(file);
        return -1;
    }

    unit_type units[256];
    if (std::fread(units, unit_size(), 256, file) != 256) {
        std::fclose(file);
        return -1;
    }

    if (units[0].label() != '\0' || units[0].has_leaf() || units[0].offset() == 0 || units[0].offset() >= 512) {
        std::fclose(file);
        return -1;
    }
    for (id_type i = 1; i < 256; ++i) {
        if (units[i].label() <= 0xFF && units[i].offset() >= size) {
            std::fclose(file);
            return -1;
        }
    }

    unit_type *buf;
    try {
        buf = new unit_type[size];
        for (id_type i = 0; i < 256; ++i) {
            buf[i] = units[i];
        }
    } catch (const std::bad_alloc &) {
        std::fclose(file);
        DARTS_THROW("failed to open double-array: std::bad_alloc");
    }

    if (size > 256) {
        if (std::fread(buf + 256, unit_size(), size - 256, file) != size - 256) {
            std::fclose(file);
            delete[] buf;
            return -1;
        }
    }
    std::fclose(file);

    clear();

    size_ = size;
    array_ = buf;
    buf_ = buf;
    return 0;
}

template <typename A, typename B, typename T, typename C>
int DoubleArrayImpl<A, B, T, C>::save(const char *file_name, const char *mode, std::size_t offset) const {
    if (size() == 0) {
        return -1;
    }

#ifdef _MSC_VER
    std::FILE *file;
    if (::fopen_s(&file, file_name, mode) != 0) {
        return -1;
    }
#else
    std::FILE *file = std::fopen(file_name, mode);
    if (file == NULL) {
        return -1;
    }
#endif

    if (std::fseek(file, offset, SEEK_SET) != 0) {
        std::fclose(file);
        return -1;
    }

    if (std::fwrite(array_, unit_size(), size(), file) != size()) {
        std::fclose(file);
        return -1;
    }
    std::fclose(file);
    return 0;
}

template <typename A, typename B, typename T, typename C>
template <typename U>
inline U DoubleArrayImpl<A, B, T, C>::exactMatchSearch(const key_type *key, std::size_t length, std::size_t node_pos) const {
    U result;
    set_result(&result, static_cast<value_type>(-1), 0);

    unit_type unit = array_[node_pos];
    if (length != 0) {
        for (std::size_t i = 0; i < length; ++i) {
            node_pos ^= unit.offset() ^ static_cast<uchar_type>(key[i]);
            unit = array_[node_pos];
            if (unit.label() != static_cast<uchar_type>(key[i])) {
                return result;
            }
        }
    } else {
        for (; key[length] != '\0'; ++length) {
            node_pos ^= unit.offset() ^ static_cast<uchar_type>(key[length]);
            unit = array_[node_pos];
            if (unit.label() != static_cast<uchar_type>(key[length])) {
                return result;
            }
        }
    }

    if (!unit.has_leaf()) {
        return result;
    }
    unit = array_[node_pos ^ unit.offset()];
    set_result(&result, static_cast<value_type>(unit.value()), length);
    return result;
}

template <typename A, typename B, typename T, typename C>
template <typename U>
inline std::size_t DoubleArrayImpl<A, B, T, C>::commonPrefixSearch(const key_type *key,
                                                                   U *results,
                                                                   std::size_t max_num_results,
                                                                   std::size_t length,
                                                                   std::size_t node_pos) const {
    std::size_t num_results = 0;

    unit_type unit = array_[node_pos];
    node_pos ^= unit.offset();
    if (length != 0) {
        for (std::size_t i = 0; i < length; ++i) {
            node_pos ^= static_cast<uchar_type>(key[i]);
            unit = array_[node_pos];
            if (unit.label() != static_cast<uchar_type>(key[i])) {
                return num_results;
            }

            node_pos ^= unit.offset();
            if (unit.has_leaf()) {
                if (num_results < max_num_results) {
                    set_result(&results[num_results], static_cast<value_type>(array_[node_pos].value()), i + 1);
                }
                ++num_results;
            }
        }
    } else {
        for (; key[length] != '\0'; ++length) {
            node_pos ^= static_cast<uchar_type>(key[length]);
            unit = array_[node_pos];
            if (unit.label() != static_cast<uchar_type>(key[length])) {
                return num_results;
            }

            node_pos ^= unit.offset();
            if (unit.has_leaf()) {
                if (num_results < max_num_results) {
                    set_result(&results[num_results], static_cast<value_type>(array_[node_pos].value()), length + 1);
                }
                ++num_results;
            }
        }
    }

    return num_results;
}

template <typename A, typename B, typename T, typename C>
inline typename DoubleArrayImpl<A, B, T, C>::value_type
DoubleArrayImpl<A, B, T, C>::traverse(const key_type *key, std::size_t &node_pos, std::size_t &key_pos, std::size_t length) const {
    id_type id = static_cast<id_type>(node_pos);
    unit_type unit = array_[id];

    if (length != 0) {
        for (; key_pos < length; ++key_pos) {
            id ^= unit.offset() ^ static_cast<uchar_type>(key[key_pos]);
            unit = array_[id];
            if (unit.label() != static_cast<uchar_type>(key[key_pos])) {
                return static_cast<value_type>(-2);
            }
            node_pos = id;
        }
    } else {
        for (; key[key_pos] != '\0'; ++key_pos) {
            id ^= unit.offset() ^ static_cast<uchar_type>(key[key_pos]);
            unit = array_[id];
            if (unit.label() != static_cast<uchar_type>(key[key_pos])) {
                return static_cast<value_type>(-2);
            }
            node_pos = id;
        }
    }

    if (!unit.has_leaf()) {
        return static_cast<value_type>(-1);
    }
    unit = array_[id ^ unit.offset()];
    return static_cast<value_type>(unit.value());
}

namespace Details {

//
// Memory management of array.
//

template <typename T>
class AutoArray {
public:
    explicit AutoArray(T *array = NULL) : array_(array) {}
    ~AutoArray() { clear(); }

    const T &operator[](std::size_t id) const { return array_[id]; }
    T &operator[](std::size_t id) { return array_[id]; }

    bool empty() const { return array_ == NULL; }

    void clear() {
        if (array_ != NULL) {
            delete[] array_;
            array_ = NULL;
        }
    }
    void swap(AutoArray *array) {
        T *temp = array_;
        array_ = array->array_;
        array->array_ = temp;
    }
    void reset(T *array = NULL) { AutoArray(array).swap(this); }

private:
    T *array_;

    // Disallows copy and assignment.
    AutoArray(const AutoArray &);
    AutoArray &operator=(const AutoArray &);
};

//
// Memory management of resizable array.
//

template <typename T>
class AutoPool {
public:
    AutoPool() : buf_(), size_(0), capacity_(0) {}
    ~AutoPool() { clear(); }

    const T &operator[](std::size_t id) const { return *(reinterpret_cast<const T *>(&buf_[0]) + id); }
    T &operator[](std::size_t id) { return *(reinterpret_cast<T *>(&buf_[0]) + id); }

    bool empty() const { return size_ == 0; }
    std::size_t size() const { return size_; }

    void clear() {
        resize(0);
        buf_.clear();
        size_ = 0;
        capacity_ = 0;
    }

    void push_back(const T &value) { append(value); }
    void pop_back() { (*this)[--size_].~T(); }

    void append() {
        if (size_ == capacity_)
            resize_buf(size_ + 1);
        new (&(*this)[size_++]) T;
    }
    void append(const T &value) {
        if (size_ == capacity_)
            resize_buf(size_ + 1);
        new (&(*this)[size_++]) T(value);
    }

    void resize(std::size_t size) {
        while (size_ > size) {
            (*this)[--size_].~T();
        }
        if (size > capacity_) {
            resize_buf(size);
        }
        while (size_ < size) {
            new (&(*this)[size_++]) T;
        }
    }
    void resize(std::size_t size, const T &value) {
        while (size_ > size) {
            (*this)[--size_].~T();
        }
        if (size > capacity_) {
            resize_buf(size);
        }
        while (size_ < size) {
            new (&(*this)[size_++]) T(value);
        }
    }

    void reserve(std::size_t size) {
        if (size > capacity_) {
            resize_buf(size);
        }
    }

private:
    AutoArray<char> buf_;
    std::size_t size_;
    std::size_t capacity_;

    // Disallows copy and assignment.
    AutoPool(const AutoPool &);
    AutoPool &operator=(const AutoPool &);

    void resize_buf(std::size_t size);
};

template <typename T>
void AutoPool<T>::resize_buf(std::size_t size) {
    std::size_t capacity;
    if (size >= capacity_ * 2) {
        capacity = size;
    } else {
        capacity = 1;
        while (capacity < size) {
            capacity <<= 1;
        }
    }

    AutoArray<char> buf;
    try {
        buf.reset(new char[sizeof(T) * capacity]);
    } catch (const std::bad_alloc &) {
        DARTS_THROW("failed to resize pool: std::bad_alloc");
    }

    if (size_ > 0) {
        T *src = reinterpret_cast<T *>(&buf_[0]);
        T *dest = reinterpret_cast<T *>(&buf[0]);
        for (std::size_t i = 0; i < size_; ++i) {
            new (&dest[i]) T(src[i]);
            src[i].~T();
        }
    }

    buf_.swap(&buf);
    capacity_ = capacity;
}

//
// Memory management of stack.
//

template <typename T>
class AutoStack {
public:
    AutoStack() : pool_() {}
    ~AutoStack() { clear(); }

    const T &top() const { return pool_[size() - 1]; }
    T &top() { return pool_[size() - 1]; }

    bool empty() const { return pool_.empty(); }
    std::size_t size() const { return pool_.size(); }

    void push(const T &value) { pool_.push_back(value); }
    void pop() { pool_.pop_back(); }

    void clear() { pool_.clear(); }

private:
    AutoPool<T> pool_;

    // Disallows copy and assignment.
    AutoStack(const AutoStack &);
    AutoStack &operator=(const AutoStack &);
};

//
// Succinct bit vector.
//

class BitVector {
public:
    BitVector() : units_(), ranks_(), num_ones_(0), size_(0) {}
    ~BitVector() { clear(); }

    bool operator[](std::size_t id) const { return (units_[id / UNIT_SIZE] >> (id % UNIT_SIZE) & 1) == 1; }

    id_type rank(std::size_t id) const {
        std::size_t unit_id = id / UNIT_SIZE;
        return ranks_[unit_id] + pop_count(units_[unit_id] & (~0U >> (UNIT_SIZE - (id % UNIT_SIZE) - 1)));
    }

    void set(std::size_t id, bool bit) {
        if (bit) {
            units_[id / UNIT_SIZE] |= 1U << (id % UNIT_SIZE);
        } else {
            units_[id / UNIT_SIZE] &= ~(1U << (id % UNIT_SIZE));
        }
    }

    bool empty() const { return units_.empty(); }
    std::size_t num_ones() const { return num_ones_; }
    std::size_t size() const { return size_; }

    void append() {
        if ((size_ % UNIT_SIZE) == 0) {
            units_.append(0);
        }
        ++size_;
    }
    void build();

    void clear() {
        units_.clear();
        ranks_.clear();
    }

private:
    enum { UNIT_SIZE = sizeof(id_type) * 8 };

    AutoPool<id_type> units_;
    AutoArray<id_type> ranks_;
    std::size_t num_ones_;
    std::size_t size_;

    // Disallows copy and assignment.
    BitVector(const BitVector &);
    BitVector &operator=(const BitVector &);

    static id_type pop_count(id_type unit) {
        unit = ((unit & 0xAAAAAAAA) >> 1) + (unit & 0x55555555);
        unit = ((unit & 0xCCCCCCCC) >> 2) + (unit & 0x33333333);
        unit = ((unit >> 4) + unit) & 0x0F0F0F0F;
        unit += unit >> 8;
        unit += unit >> 16;
        return unit & 0xFF;
    }
};

inline void BitVector::build() {
    try {
        ranks_.reset(new id_type[units_.size()]);
    } catch (const std::bad_alloc &) {
        DARTS_THROW("failed to build rank index: std::bad_alloc");
    }

    num_ones_ = 0;
    for (std::size_t i = 0; i < units_.size(); ++i) {
        ranks_[i] = num_ones_;
        num_ones_ += pop_count(units_[i]);
    }
}

//
// Keyset.
//

template <typename T>
class Keyset {
public:
    Keyset(std::size_t num_keys, const char_type *const *keys, const std::size_t *lengths, const T *values)
        : num_keys_(num_keys), keys_(keys), lengths_(lengths), values_(values) {}

    std::size_t num_keys() const { return num_keys_; }
    const char_type *keys(std::size_t id) const { return keys_[id]; }
    uchar_type keys(std::size_t key_id, std::size_t char_id) const {
        if (has_lengths() && char_id >= lengths_[key_id])
            return '\0';
        return keys_[key_id][char_id];
    }

    bool has_lengths() const { return lengths_ != NULL; }
    std::size_t lengths(std::size_t id) const {
        if (has_lengths()) {
            return lengths_[id];
        }
        std::size_t length = 0;
        while (keys_[id][length] != '\0') {
            ++length;
        }
        return length;
    }

    bool has_values() const { return values_ != NULL; }
    value_type values(std::size_t id) const {
        if (has_values()) {
            return static_cast<value_type>(values_[id]);
        }
        return static_cast<value_type>(id);
    }

private:
    std::size_t num_keys_;
    const char_type *const *keys_;
    const std::size_t *lengths_;
    const T *values_;

    // Disallows copy and assignment.
    Keyset(const Keyset &);
    Keyset &operator=(const Keyset &);
};

//
// Node of Directed Acyclic Word Graph (DAWG).
//

class DawgNode {
public:
    DawgNode() : child_(0), sibling_(0), label_('\0'), is_state_(false), has_sibling_(false) {}

    void set_child(id_type child) { child_ = child; }
    void set_sibling(id_type sibling) { sibling_ = sibling; }
    void set_value(value_type value) { child_ = value; }
    void set_label(uchar_type label) { label_ = label; }
    void set_is_state(bool is_state) { is_state_ = is_state; }
    void set_has_sibling(bool has_sibling) { has_sibling_ = has_sibling; }

    id_type child() const { return child_; }
    id_type sibling() const { return sibling_; }
    value_type value() const { return static_cast<value_type>(child_); }
    uchar_type label() const { return label_; }
    bool is_state() const { return is_state_; }
    bool has_sibling() const { return has_sibling_; }

    id_type unit() const {
        if (label_ == '\0') {
            return (child_ << 1) | (has_sibling_ ? 1 : 0);
        }
        return (child_ << 2) | (is_state_ ? 2 : 0) | (has_sibling_ ? 1 : 0);
    }

private:
    id_type child_;
    id_type sibling_;
    uchar_type label_;
    bool is_state_;
    bool has_sibling_;

    // Copyable.
};

//
// Fixed unit of Directed Acyclic Word Graph (DAWG).
//

class DawgUnit {
public:
    explicit DawgUnit(id_type unit = 0) : unit_(unit) {}
    DawgUnit(const DawgUnit &unit) : unit_(unit.unit_) {}

    DawgUnit &operator=(id_type unit) {
        unit_ = unit;
        return *this;
    }

    id_type unit() const { return unit_; }

    id_type child() const { return unit_ >> 2; }
    bool has_sibling() const { return (unit_ & 1) == 1; }
    value_type value() const { return static_cast<value_type>(unit_ >> 1); }
    bool is_state() const { return (unit_ & 2) == 2; }

private:
    id_type unit_;

    // Copyable.
};

//
// Directed Acyclic Word Graph (DAWG) builder.
//

class DawgBuilder {
public:
    DawgBuilder() : nodes_(), units_(), labels_(), is_intersections_(), table_(), node_stack_(), recycle_bin_(), num_states_(0) {}
    ~DawgBuilder() { clear(); }

    id_type root() const { return 0; }

    id_type child(id_type id) const { return units_[id].child(); }
    id_type sibling(id_type id) const { return units_[id].has_sibling() ? (id + 1) : 0; }
    int value(id_type id) const { return units_[id].value(); }

    bool is_leaf(id_type id) const { return label(id) == '\0'; }
    uchar_type label(id_type id) const { return labels_[id]; }

    bool is_intersection(id_type id) const { return is_intersections_[id]; }
    id_type intersection_id(id_type id) const { return is_intersections_.rank(id) - 1; }

    std::size_t num_intersections() const { return is_intersections_.num_ones(); }

    std::size_t size() const { return units_.size(); }

    void init();
    void finish();

    void insert(const char *key, std::size_t length, value_type value);

    void clear();

private:
    enum { INITIAL_TABLE_SIZE = 1 << 10 };

    AutoPool<DawgNode> nodes_;
    AutoPool<DawgUnit> units_;
    AutoPool<uchar_type> labels_;
    BitVector is_intersections_;
    AutoPool<id_type> table_;
    AutoStack<id_type> node_stack_;
    AutoStack<id_type> recycle_bin_;
    std::size_t num_states_;

    // Disallows copy and assignment.
    DawgBuilder(const DawgBuilder &);
    DawgBuilder &operator=(const DawgBuilder &);

    void flush(id_type id);

    void expand_table();

    id_type find_unit(id_type id, id_type *hash_id) const;
    id_type find_node(id_type node_id, id_type *hash_id) const;

    bool are_equal(id_type node_id, id_type unit_id) const;

    id_type hash_unit(id_type id) const;
    id_type hash_node(id_type id) const;

    id_type append_node();
    id_type append_unit();

    void free_node(id_type id) { recycle_bin_.push(id); }

    static id_type hash(id_type key) {
        key = ~key + (key << 15); // key = (key << 15) - key - 1;
        key = key ^ (key >> 12);
        key = key + (key << 2);
        key = key ^ (key >> 4);
        key = key * 2057; // key = (key + (key << 3)) + (key << 11);
        key = key ^ (key >> 16);
        return key;
    }
};

inline void DawgBuilder::init() {
    table_.resize(INITIAL_TABLE_SIZE, 0);

    append_node();
    append_unit();

    num_states_ = 1;

    nodes_[0].set_label(0xFF);
    node_stack_.push(0);
}

inline void DawgBuilder::finish() {
    flush(0);

    units_[0] = nodes_[0].unit();
    labels_[0] = nodes_[0].label();

    nodes_.clear();
    table_.clear();
    node_stack_.clear();
    recycle_bin_.clear();

    is_intersections_.build();
}

inline void DawgBuilder::insert(const char *key, std::size_t length, value_type value) {
    if (value < 0) {
        DARTS_THROW("failed to insert key: negative value");
    } else if (length == 0) {
        DARTS_THROW("failed to insert key: zero-length key");
    }

    id_type id = 0;
    std::size_t key_pos = 0;

    for (; key_pos <= length; ++key_pos) {
        id_type child_id = nodes_[id].child();
        if (child_id == 0) {
            break;
        }

        uchar_type key_label = static_cast<uchar_type>(key[key_pos]);
        if (key_pos < length && key_label == '\0') {
            DARTS_THROW("failed to insert key: invalid null character");
        }

        uchar_type unit_label = nodes_[child_id].label();
        if (key_label < unit_label) {
            DARTS_THROW("failed to insert key: wrong key order");
        } else if (key_label > unit_label) {
            nodes_[child_id].set_has_sibling(true);
            flush(child_id);
            break;
        }
        id = child_id;
    }

    if (key_pos > length) {
        return;
    }

    for (; key_pos <= length; ++key_pos) {
        uchar_type key_label = static_cast<uchar_type>((key_pos < length) ? key[key_pos] : '\0');
        id_type child_id = append_node();

        if (nodes_[id].child() == 0) {
            nodes_[child_id].set_is_state(true);
        }
        nodes_[child_id].set_sibling(nodes_[id].child());
        nodes_[child_id].set_label(key_label);
        nodes_[id].set_child(child_id);
        node_stack_.push(child_id);

        id = child_id;
    }
    nodes_[id].set_value(value);
}

inline void DawgBuilder::clear() {
    nodes_.clear();
    units_.clear();
    labels_.clear();
    is_intersections_.clear();
    table_.clear();
    node_stack_.clear();
    recycle_bin_.clear();
    num_states_ = 0;
}

inline void DawgBuilder::flush(id_type id) {
    while (node_stack_.top() != id) {
        id_type node_id = node_stack_.top();
        node_stack_.pop();

        if (num_states_ >= table_.size() - (table_.size() >> 2)) {
            expand_table();
        }

        id_type num_siblings = 0;
        for (id_type i = node_id; i != 0; i = nodes_[i].sibling()) {
            ++num_siblings;
        }

        id_type hash_id;
        id_type match_id = find_node(node_id, &hash_id);
        if (match_id != 0) {
            is_intersections_.set(match_id, true);
        } else {
            id_type unit_id = 0;
            for (id_type i = 0; i < num_siblings; ++i) {
                unit_id = append_unit();
            }
            for (id_type i = node_id; i != 0; i = nodes_[i].sibling()) {
                units_[unit_id] = nodes_[i].unit();
                labels_[unit_id] = nodes_[i].label();
                --unit_id;
            }
            match_id = unit_id + 1;
            table_[hash_id] = match_id;
            ++num_states_;
        }

        for (id_type i = node_id, next; i != 0; i = next) {
            next = nodes_[i].sibling();
            free_node(i);
        }

        nodes_[node_stack_.top()].set_child(match_id);
    }
    node_stack_.pop();
}

inline void DawgBuilder::expand_table() {
    std::size_t table_size = table_.size() << 1;
    table_.clear();
    table_.resize(table_size, 0);

    for (std::size_t i = 1; i < units_.size(); ++i) {
        id_type id = static_cast<id_type>(i);
        if (labels_[id] == '\0' || units_[id].is_state()) {
            id_type hash_id;
            find_unit(id, &hash_id);
            table_[hash_id] = id;
        }
    }
}

inline id_type DawgBuilder::find_unit(id_type id, id_type *hash_id) const {
    *hash_id = hash_unit(id) % table_.size();
    for (;; *hash_id = (*hash_id + 1) % table_.size()) {
        id_type unit_id = table_[*hash_id];
        if (unit_id == 0) {
            break;
        }

        // There must not be the same unit.
    }
    return 0;
}

inline id_type DawgBuilder::find_node(id_type node_id, id_type *hash_id) const {
    *hash_id = hash_node(node_id) % table_.size();
    for (;; *hash_id = (*hash_id + 1) % table_.size()) {
        id_type unit_id = table_[*hash_id];
        if (unit_id == 0) {
            break;
        }

        if (are_equal(node_id, unit_id)) {
            return unit_id;
        }
    }
    return 0;
}

inline bool DawgBuilder::are_equal(id_type node_id, id_type unit_id) const {
    for (id_type i = nodes_[node_id].sibling(); i != 0; i = nodes_[i].sibling()) {
        if (units_[unit_id].has_sibling() == false) {
            return false;
        }
        ++unit_id;
    }
    if (units_[unit_id].has_sibling() == true) {
        return false;
    }

    for (id_type i = node_id; i != 0; i = nodes_[i].sibling(), --unit_id) {
        if (nodes_[i].unit() != units_[unit_id].unit() || nodes_[i].label() != labels_[unit_id]) {
            return false;
        }
    }
    return true;
}

inline id_type DawgBuilder::hash_unit(id_type id) const {
    id_type hash_value = 0;
    for (; id != 0; ++id) {
        id_type unit = units_[id].unit();
        uchar_type label = labels_[id];
        hash_value ^= hash((label << 24) ^ unit);

        if (units_[id].has_sibling() == false) {
            break;
        }
    }
    return hash_value;
}

inline id_type DawgBuilder::hash_node(id_type id) const {
    id_type hash_value = 0;
    for (; id != 0; id = nodes_[id].sibling()) {
        id_type unit = nodes_[id].unit();
        uchar_type label = nodes_[id].label();
        hash_value ^= hash((label << 24) ^ unit);
    }
    return hash_value;
}

inline id_type DawgBuilder::append_unit() {
    is_intersections_.append();
    units_.append();
    labels_.append();

    return static_cast<id_type>(is_intersections_.size() - 1);
}

inline id_type DawgBuilder::append_node() {
    id_type id;
    if (recycle_bin_.empty()) {
        id = static_cast<id_type>(nodes_.size());
        nodes_.append();
    } else {
        id = recycle_bin_.top();
        nodes_[id] = DawgNode();
        recycle_bin_.pop();
    }
    return id;
}

//
// Unit of double-array builder.
//

class DoubleArrayBuilderUnit {
public:
    DoubleArrayBuilderUnit() : unit_(0) {}

    void set_has_leaf(bool has_leaf) {
        if (has_leaf) {
            unit_ |= 1U << 8;
        } else {
            unit_ &= ~(1U << 8);
        }
    }
    void set_value(value_type value) { unit_ = value | (1U << 31); }
    void set_label(uchar_type label) { unit_ = (unit_ & ~0xFFU) | label; }
    void set_offset(id_type offset) {
        if (offset >= 1U << 29) {
            DARTS_THROW("failed to modify unit: too large offset");
        }
        unit_ &= (1U << 31) | (1U << 8) | 0xFF;
        if (offset < 1U << 21) {
            unit_ |= (offset << 10);
        } else {
            unit_ |= (offset << 2) | (1U << 9);
        }
    }

private:
    id_type unit_;

    // Copyable.
};

//
// Extra unit of double-array builder.
//

class DoubleArrayBuilderExtraUnit {
public:
    DoubleArrayBuilderExtraUnit() : prev_(0), next_(0), is_fixed_(false), is_used_(false) {}

    void set_prev(id_type prev) { prev_ = prev; }
    void set_next(id_type next) { next_ = next; }
    void set_is_fixed(bool is_fixed) { is_fixed_ = is_fixed; }
    void set_is_used(bool is_used) { is_used_ = is_used; }

    id_type prev() const { return prev_; }
    id_type next() const { return next_; }
    bool is_fixed() const { return is_fixed_; }
    bool is_used() const { return is_used_; }

private:
    id_type prev_;
    id_type next_;
    bool is_fixed_;
    bool is_used_;

    // Copyable.
};

//
// DAWG -> double-array converter.
//

class DoubleArrayBuilder {
public:
    explicit DoubleArrayBuilder(progress_func_type progress_func)
        : progress_func_(progress_func), units_(), extras_(), labels_(), table_(), extras_head_(0) {}
    ~DoubleArrayBuilder() { clear(); }

    template <typename T>
    void build(const Keyset<T> &keyset);
    void copy(std::size_t *size_ptr, DoubleArrayUnit **buf_ptr) const;

    void clear();

private:
    static constexpr auto BLOCK_SIZE = 256;
    static constexpr auto NUM_EXTRA_BLOCKS = 16;
    static constexpr auto NUM_EXTRAS = BLOCK_SIZE * NUM_EXTRA_BLOCKS;

    enum { UPPER_MASK = 0xFF << 21 };
    enum { LOWER_MASK = 0xFF };

    typedef DoubleArrayBuilderUnit unit_type;
    typedef DoubleArrayBuilderExtraUnit extra_type;

    progress_func_type progress_func_;
    AutoPool<unit_type> units_;
    AutoArray<extra_type> extras_;
    AutoPool<uchar_type> labels_;
    AutoArray<id_type> table_;
    id_type extras_head_;

    // Disallows copy and assignment.
    DoubleArrayBuilder(const DoubleArrayBuilder &);
    DoubleArrayBuilder &operator=(const DoubleArrayBuilder &);

    std::size_t num_blocks() const { return units_.size() / BLOCK_SIZE; }

    const extra_type &extras(id_type id) const { return extras_[id % NUM_EXTRAS]; }
    extra_type &extras(id_type id) { return extras_[id % NUM_EXTRAS]; }

    template <typename T>
    void build_dawg(const Keyset<T> &keyset, DawgBuilder *dawg_builder);
    void build_from_dawg(const DawgBuilder &dawg);
    void build_from_dawg(const DawgBuilder &dawg, id_type dawg_id, id_type dic_id);
    id_type arrange_from_dawg(const DawgBuilder &dawg, id_type dawg_id, id_type dic_id);

    template <typename T>
    void build_from_keyset(const Keyset<T> &keyset);
    template <typename T>
    void build_from_keyset(const Keyset<T> &keyset, std::size_t begin, std::size_t end, std::size_t depth, id_type dic_id);
    template <typename T>
    id_type arrange_from_keyset(const Keyset<T> &keyset, std::size_t begin, std::size_t end, std::size_t depth, id_type dic_id);

    id_type find_valid_offset(id_type id) const;
    bool is_valid_offset(id_type id, id_type offset) const;

    void reserve_id(id_type id);
    void expand_units();

    void fix_all_blocks();
    void fix_block(id_type block_id);
};

template <typename T>
void DoubleArrayBuilder::build(const Keyset<T> &keyset) {
    if (keyset.has_values()) {
        Details::DawgBuilder dawg_builder;
        build_dawg(keyset, &dawg_builder);
        build_from_dawg(dawg_builder);
        dawg_builder.clear();
    } else {
        build_from_keyset(keyset);
    }
}

inline void DoubleArrayBuilder::copy(std::size_t *size_ptr, DoubleArrayUnit **buf_ptr) const {
    if (size_ptr != NULL) {
        *size_ptr = units_.size();
    }
    if (buf_ptr != NULL) {
        *buf_ptr = new DoubleArrayUnit[units_.size()];
        unit_type *units = reinterpret_cast<unit_type *>(*buf_ptr);
        for (std::size_t i = 0; i < units_.size(); ++i) {
            units[i] = units_[i];
        }
    }
}

inline void DoubleArrayBuilder::clear() {
    units_.clear();
    extras_.clear();
    labels_.clear();
    table_.clear();
    extras_head_ = 0;
}

template <typename T>
void DoubleArrayBuilder::build_dawg(const Keyset<T> &keyset, DawgBuilder *dawg_builder) {
    dawg_builder->init();
    for (std::size_t i = 0; i < keyset.num_keys(); ++i) {
        dawg_builder->insert(keyset.keys(i), keyset.lengths(i), keyset.values(i));
        if (progress_func_ != NULL) {
            progress_func_(i + 1, keyset.num_keys() + 1);
        }
    }
    dawg_builder->finish();
}

inline void DoubleArrayBuilder::build_from_dawg(const DawgBuilder &dawg) {
    std::size_t num_units = 1;
    while (num_units < dawg.size()) {
        num_units <<= 1;
    }
    units_.reserve(num_units);

    table_.reset(new id_type[dawg.num_intersections()]);
    for (std::size_t i = 0; i < dawg.num_intersections(); ++i) {
        table_[i] = 0;
    }

    extras_.reset(new extra_type[NUM_EXTRAS]);

    reserve_id(0);
    extras(0).set_is_used(true);
    units_[0].set_offset(1);
    units_[0].set_label('\0');

    if (dawg.child(dawg.root()) != 0) {
        build_from_dawg(dawg, dawg.root(), 0);
    }

    fix_all_blocks();

    extras_.clear();
    labels_.clear();
    table_.clear();
}

inline void DoubleArrayBuilder::build_from_dawg(const DawgBuilder &dawg, id_type dawg_id, id_type dic_id) {
    id_type dawg_child_id = dawg.child(dawg_id);
    if (dawg.is_intersection(dawg_child_id)) {
        id_type intersection_id = dawg.intersection_id(dawg_child_id);
        id_type offset = table_[intersection_id];
        if (offset != 0) {
            offset ^= dic_id;
            if (!(offset & UPPER_MASK) || !(offset & LOWER_MASK)) {
                if (dawg.is_leaf(dawg_child_id)) {
                    units_[dic_id].set_has_leaf(true);
                }
                units_[dic_id].set_offset(offset);
                return;
            }
        }
    }

    id_type offset = arrange_from_dawg(dawg, dawg_id, dic_id);
    if (dawg.is_intersection(dawg_child_id)) {
        table_[dawg.intersection_id(dawg_child_id)] = offset;
    }

    do {
        uchar_type child_label = dawg.label(dawg_child_id);
        id_type dic_child_id = offset ^ child_label;
        if (child_label != '\0') {
            build_from_dawg(dawg, dawg_child_id, dic_child_id);
        }
        dawg_child_id = dawg.sibling(dawg_child_id);
    } while (dawg_child_id != 0);
}

inline id_type DoubleArrayBuilder::arrange_from_dawg(const DawgBuilder &dawg, id_type dawg_id, id_type dic_id) {
    labels_.resize(0);

    id_type dawg_child_id = dawg.child(dawg_id);
    while (dawg_child_id != 0) {
        labels_.append(dawg.label(dawg_child_id));
        dawg_child_id = dawg.sibling(dawg_child_id);
    }

    id_type offset = find_valid_offset(dic_id);
    units_[dic_id].set_offset(dic_id ^ offset);

    dawg_child_id = dawg.child(dawg_id);
    for (std::size_t i = 0; i < labels_.size(); ++i) {
        id_type dic_child_id = offset ^ labels_[i];
        reserve_id(dic_child_id);

        if (dawg.is_leaf(dawg_child_id)) {
            units_[dic_id].set_has_leaf(true);
            units_[dic_child_id].set_value(dawg.value(dawg_child_id));
        } else {
            units_[dic_child_id].set_label(labels_[i]);
        }

        dawg_child_id = dawg.sibling(dawg_child_id);
    }
    extras(offset).set_is_used(true);

    return offset;
}

template <typename T>
void DoubleArrayBuilder::build_from_keyset(const Keyset<T> &keyset) {
    std::size_t num_units = 1;
    while (num_units < keyset.num_keys()) {
        num_units <<= 1;
    }
    units_.reserve(num_units);

    extras_.reset(new extra_type[NUM_EXTRAS]);

    reserve_id(0);
    extras(0).set_is_used(true);
    units_[0].set_offset(1);
    units_[0].set_label('\0');

    if (keyset.num_keys() > 0) {
        build_from_keyset(keyset, 0, keyset.num_keys(), 0, 0);
    }

    fix_all_blocks();

    extras_.clear();
    labels_.clear();
}

template <typename T>
void DoubleArrayBuilder::build_from_keyset(const Keyset<T> &keyset, std::size_t begin, std::size_t end, std::size_t depth, id_type dic_id) {
    id_type offset = arrange_from_keyset(keyset, begin, end, depth, dic_id);

    while (begin < end) {
        if (keyset.keys(begin, depth) != '\0') {
            break;
        }
        ++begin;
    }
    if (begin == end) {
        return;
    }

    std::size_t last_begin = begin;
    uchar_type last_label = keyset.keys(begin, depth);
    while (++begin < end) {
        uchar_type label = keyset.keys(begin, depth);
        if (label != last_label) {
            build_from_keyset(keyset, last_begin, begin, depth + 1, offset ^ last_label);
            last_begin = begin;
            last_label = keyset.keys(begin, depth);
        }
    }
    build_from_keyset(keyset, last_begin, end, depth + 1, offset ^ last_label);
}

template <typename T>
id_type DoubleArrayBuilder::arrange_from_keyset(const Keyset<T> &keyset, std::size_t begin, std::size_t end, std::size_t depth, id_type dic_id) {
    labels_.resize(0);

    value_type value = -1;
    for (std::size_t i = begin; i < end; ++i) {
        uchar_type label = keyset.keys(i, depth);
        if (label == '\0') {
            if (keyset.has_lengths() && depth < keyset.lengths(i)) {
                DARTS_THROW("failed to build double-array: "
                            "invalid null character");
            } else if (keyset.values(i) < 0) {
                DARTS_THROW("failed to build double-array: negative value");
            }

            if (value == -1) {
                value = keyset.values(i);
            }
            if (progress_func_ != NULL) {
                progress_func_(i + 1, keyset.num_keys() + 1);
            }
        }

        if (labels_.empty()) {
            labels_.append(label);
        } else if (label != labels_[labels_.size() - 1]) {
            if (label < labels_[labels_.size() - 1]) {
                DARTS_THROW("failed to build double-array: wrong key order");
            }
            labels_.append(label);
        }
    }

    id_type offset = find_valid_offset(dic_id);
    units_[dic_id].set_offset(dic_id ^ offset);

    for (std::size_t i = 0; i < labels_.size(); ++i) {
        id_type dic_child_id = offset ^ labels_[i];
        reserve_id(dic_child_id);
        if (labels_[i] == '\0') {
            units_[dic_id].set_has_leaf(true);
            units_[dic_child_id].set_value(value);
        } else {
            units_[dic_child_id].set_label(labels_[i]);
        }
    }
    extras(offset).set_is_used(true);

    return offset;
}

inline id_type DoubleArrayBuilder::find_valid_offset(id_type id) const {
    if (extras_head_ >= units_.size()) {
        return units_.size() | (id & LOWER_MASK);
    }

    id_type unfixed_id = extras_head_;
    do {
        id_type offset = unfixed_id ^ labels_[0];
        if (is_valid_offset(id, offset)) {
            return offset;
        }
        unfixed_id = extras(unfixed_id).next();
    } while (unfixed_id != extras_head_);

    return units_.size() | (id & LOWER_MASK);
}

inline bool DoubleArrayBuilder::is_valid_offset(id_type id, id_type offset) const {
    if (extras(offset).is_used()) {
        return false;
    }

    id_type rel_offset = id ^ offset;
    if ((rel_offset & LOWER_MASK) && (rel_offset & UPPER_MASK)) {
        return false;
    }

    for (std::size_t i = 1; i < labels_.size(); ++i) {
        if (extras(offset ^ labels_[i]).is_fixed()) {
            return false;
        }
    }

    return true;
}

inline void DoubleArrayBuilder::reserve_id(id_type id) {
    if (id >= units_.size()) {
        expand_units();
    }

    if (id == extras_head_) {
        extras_head_ = extras(id).next();
        if (extras_head_ == id) {
            extras_head_ = units_.size();
        }
    }
    extras(extras(id).prev()).set_next(extras(id).next());
    extras(extras(id).next()).set_prev(extras(id).prev());
    extras(id).set_is_fixed(true);
}

inline void DoubleArrayBuilder::expand_units() {
    id_type src_num_units = units_.size();
    id_type src_num_blocks = num_blocks();

    id_type dest_num_units = src_num_units + BLOCK_SIZE;
    id_type dest_num_blocks = src_num_blocks + 1;

    if (dest_num_blocks > NUM_EXTRA_BLOCKS) {
        fix_block(src_num_blocks - NUM_EXTRA_BLOCKS);
    }

    units_.resize(dest_num_units);

    if (dest_num_blocks > NUM_EXTRA_BLOCKS) {
        for (std::size_t id = src_num_units; id < dest_num_units; ++id) {
            extras(id).set_is_used(false);
            extras(id).set_is_fixed(false);
        }
    }

    for (id_type i = src_num_units + 1; i < dest_num_units; ++i) {
        extras(i - 1).set_next(i);
        extras(i).set_prev(i - 1);
    }

    extras(src_num_units).set_prev(dest_num_units - 1);
    extras(dest_num_units - 1).set_next(src_num_units);

    extras(src_num_units).set_prev(extras(extras_head_).prev());
    extras(dest_num_units - 1).set_next(extras_head_);

    extras(extras(extras_head_).prev()).set_next(src_num_units);
    extras(extras_head_).set_prev(dest_num_units - 1);
}

inline void DoubleArrayBuilder::fix_all_blocks() {
    id_type begin = 0;
    if (num_blocks() > NUM_EXTRA_BLOCKS) {
        begin = num_blocks() - NUM_EXTRA_BLOCKS;
    }
    id_type end = num_blocks();

    for (id_type block_id = begin; block_id != end; ++block_id) {
        fix_block(block_id);
    }
}

inline void DoubleArrayBuilder::fix_block(id_type block_id) {
    id_type begin = block_id * BLOCK_SIZE;
    id_type end = begin + BLOCK_SIZE;

    id_type unused_offset = 0;
    for (id_type offset = begin; offset != end; ++offset) {
        if (!extras(offset).is_used()) {
            unused_offset = offset;
            break;
        }
    }

    for (id_type id = begin; id != end; ++id) {
        if (!extras(id).is_fixed()) {
            reserve_id(id);
            units_[id].set_label(static_cast<uchar_type>(id ^ unused_offset));
        }
    }
}

} // namespace Details

//
// Member function build() of DoubleArrayImpl.
//

template <typename A, typename B, typename T, typename C>
int DoubleArrayImpl<A, B, T, C>::build(std::size_t num_keys,
                                       const key_type *const *keys,
                                       const std::size_t *lengths,
                                       const value_type *values,
                                       Details::progress_func_type progress_func) {
    Details::Keyset<value_type> keyset(num_keys, keys, lengths, values);

    Details::DoubleArrayBuilder builder(progress_func);
    builder.build(keyset);

    std::size_t size = 0;
    unit_type *buf = NULL;
    builder.copy(&size, &buf);

    clear();

    size_ = size;
    array_ = buf;
    buf_ = buf;

    if (progress_func != NULL) {
        progress_func(num_keys + 1, num_keys + 1);
    }

    return 0;
}

} // namespace Darts

#undef DARTS_INT_TO_STR
#undef DARTS_LINE_TO_STR
#undef DARTS_LINE_STR
#undef DARTS_THROW

#endif // DARTS_H_