src/third_party/WebKit/Source/WTF/wtf/SegmentedVector.h

/*
 * Copyright (C) 2008 Apple Inc. All rights reserved.
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 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 * 1.  Redistributions of source code must retain the above copyright
 *     notice, this list of conditions and the following disclaimer.
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 *     its contributors may be used to endorse or promote products derived
 *     from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY APPLE AND ITS CONTRIBUTORS "AS IS" AND ANY
 * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
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 */

#ifndef SegmentedVector_h
#define SegmentedVector_h

#include <wtf/Vector.h>

namespace WTF {

    // An iterator for SegmentedVector. It supports only the pre ++ operator
    template <typename T, size_t SegmentSize = 8, size_t InlineCapacity = 32> class SegmentedVector;
    template <typename T, size_t SegmentSize = 8, size_t InlineCapacity = 32> class SegmentedVectorIterator {
    private:
        friend class SegmentedVector<T, SegmentSize, InlineCapacity>;
    public:
        typedef SegmentedVectorIterator<T, SegmentSize, InlineCapacity> Iterator;

        ~SegmentedVectorIterator() { }

        T& operator*() const { return m_vector.m_segments.at(m_segment)->at(m_index); }
        T* operator->() const { return &m_vector.m_segments.at(m_segment)->at(m_index); }

        // Only prefix ++ operator supported
        Iterator& operator++()
        {
            ASSERT(m_index != SegmentSize);
            ++m_index;
            if (m_index >= m_vector.m_segments.at(m_segment)->size())  {
                if (m_segment + 1 < m_vector.m_segments.size()) {
                    ASSERT(m_vector.m_segments.at(m_segment)->size() > 0);
                    ++m_segment;
                    m_index = 0;
                } else {
                    // Points to the "end" symbol
                    m_segment = 0;
                    m_index = SegmentSize;
                }
            }
            return *this;
        }

        bool operator==(const Iterator& other) const
        {
            return m_index == other.m_index && m_segment == other.m_segment && &m_vector == &other.m_vector;
        }

        bool operator!=(const Iterator& other) const
        {
            return m_index != other.m_index || m_segment != other.m_segment || &m_vector != &other.m_vector;
        }

        SegmentedVectorIterator& operator=(const SegmentedVectorIterator<T, SegmentSize, InlineCapacity>& other)
        {
            m_vector = other.m_vector;
            m_segment = other.m_segment;
            m_index = other.m_index;
            return *this;
        }

    private:
        SegmentedVectorIterator(SegmentedVector<T, SegmentSize, InlineCapacity>& vector, size_t segment, size_t index)
            : m_vector(vector)
            , m_segment(segment)
            , m_index(index)
        {
        }

        SegmentedVector<T, SegmentSize, InlineCapacity>& m_vector;
        size_t m_segment;
        size_t m_index;
    };

    // SegmentedVector is just like Vector, but it doesn't move the values
    // stored in its buffer when it grows. Therefore, it is safe to keep
    // pointers into a SegmentedVector. The default tuning values are
    // optimized for segmented vectors that get large; you may want to use
    // SegmentedVector<thingy, 1, 0> if you don't expect a lot of entries.
    template <typename T, size_t SegmentSize, size_t InlineCapacity>
    class SegmentedVector {
        friend class SegmentedVectorIterator<T, SegmentSize, InlineCapacity>;
    public:
        typedef SegmentedVectorIterator<T, SegmentSize, InlineCapacity> Iterator;

        SegmentedVector()
            : m_size(0)
        {
            m_segments.append(&m_inlineSegment);
        }

        ~SegmentedVector()
        {
            deleteAllSegments();
        }

        size_t size() const { return m_size; }
        bool isEmpty() const { return !size(); }

        T& at(size_t index)
        {
            if (index < SegmentSize)
                return m_inlineSegment[index];
            return segmentFor(index)->at(subscriptFor(index));
        }

        const T& at(size_t index) const
        {
            return const_cast<SegmentedVector<T, SegmentSize, InlineCapacity>*>(this)->at(index);
        }

        T& operator[](size_t index)
        {
            return at(index);
        }

        const T& operator[](size_t index) const
        {
            return at(index);
        }

        T& last()
        {
            return at(size() - 1);
        }

        template <typename U> void append(const U& value)
        {
            ++m_size;

            if (m_size <= SegmentSize) {
                m_inlineSegment.uncheckedAppend(value);
                return;
            }

            if (!segmentExistsFor(m_size - 1))
                m_segments.append(new Segment);
            segmentFor(m_size - 1)->uncheckedAppend(value);
        }

        T& alloc()
        {
            append<T>(T());
            return last();
        }

        void removeLast()
        {
            if (m_size <= SegmentSize)
                m_inlineSegment.removeLast();
            else
                segmentFor(m_size - 1)->removeLast();
            --m_size;
        }

        void grow(size_t size)
        {
            ASSERT(size > m_size);
            ensureSegmentsFor(size);
            m_size = size;
        }

        void clear()
        {
            deleteAllSegments();
            m_segments.resize(1);
            m_inlineSegment.clear();
            m_size = 0;
        }

        Iterator begin()
        {
            return Iterator(*this, 0, m_size ? 0 : SegmentSize);
        }

        Iterator end()
        {
            return Iterator(*this, 0, SegmentSize);
        }
        
        void shrinkToFit()
        {
            m_segments.shrinkToFit();
        }

    private:
        typedef Vector<T, SegmentSize> Segment;

        void deleteAllSegments()
        {
            // Skip the first segment, because it's our inline segment, which was
            // not created by new.
            for (size_t i = 1; i < m_segments.size(); i++)
                delete m_segments[i];
        }

        bool segmentExistsFor(size_t index)
        {
            return index / SegmentSize < m_segments.size();
        }

        Segment* segmentFor(size_t index)
        {
            return m_segments[index / SegmentSize];
        }

        size_t subscriptFor(size_t index)
        {
            return index % SegmentSize;
        }

        void ensureSegmentsFor(size_t size)
        {
            size_t segmentCount = m_size / SegmentSize;
            if (m_size % SegmentSize)
                ++segmentCount;
            segmentCount = std::max<size_t>(segmentCount, 1); // We always have at least our inline segment.

            size_t neededSegmentCount = size / SegmentSize;
            if (size % SegmentSize)
                ++neededSegmentCount;

            // Fill up to N - 1 segments.
            size_t end = neededSegmentCount - 1;
            for (size_t i = segmentCount - 1; i < end; ++i)
                ensureSegment(i, SegmentSize);

            // Grow segment N to accomodate the remainder.
            ensureSegment(end, subscriptFor(size - 1) + 1);
        }

        void ensureSegment(size_t segmentIndex, size_t size)
        {
            ASSERT(segmentIndex <= m_segments.size());
            if (segmentIndex == m_segments.size())
                m_segments.append(new Segment);
            m_segments[segmentIndex]->grow(size);
        }

        size_t m_size;
        Segment m_inlineSegment;
        Vector<Segment*, InlineCapacity> m_segments;
    };

} // namespace WTF

using WTF::SegmentedVector;

#endif // SegmentedVector_h