assimp.assimp/include/assimp/SmallVector.h

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/** @file Defines small vector with inplace storage.
Based on CppCon 2016: Chandler Carruth "High Performance Code 201: Hybrid Data Structures" */

#pragma once
#ifndef AI_SMALLVECTOR_H_INC
#define AI_SMALLVECTOR_H_INC

#ifdef __GNUC__
#   pragma GCC system_header
#endif

namespace Assimp {

// --------------------------------------------------------------------------------------------
/// @brief Small vector with inplace storage.
///
/// Reduces heap allocations when list is shorter. It uses a small array for a dedicated size.
/// When the growing gets bigger than this small cache a dynamic growing algorithm will be
/// used.
// --------------------------------------------------------------------------------------------
template<typename T, unsigned int Capacity>
class SmallVector {
public:
    /// @brief  The default class constructor.
    SmallVector() :
            mStorage(mInplaceStorage),
            mSize(0),
            mCapacity(Capacity) {
        // empty
    }

    /// @brief  The class destructor.
    ~SmallVector() {
        if (mStorage != mInplaceStorage) {
            delete [] mStorage;
        }
    }

    /// @brief  Will push a new item. The capacity will grow in case of a too small capacity.
    /// @param  item    [in] The item to push at the end of the vector.
    void push_back(const T& item) {
        if (mSize < mCapacity) {
            mStorage[mSize++] = item;
            return;
        }

        push_back_and_grow(item);
    }

    /// @brief  Will resize the vector.
    /// @param  newSize     [in] The new size.
    void resize(size_t newSize) {
        if (newSize > mCapacity) {
            grow(newSize);
        }
        mSize = newSize;
    }

    /// @brief  Returns the current size of the vector.
    /// @return The current size.
    size_t size() const {
        return mSize;
    }

    /// @brief  Returns a pointer to the first item.
    /// @return The first item as a pointer.
    T* begin() {
        return mStorage;
    }

    /// @brief  Returns a pointer to the end.
    /// @return The end as a pointer.
    T* end() {
        return &mStorage[mSize];
    }

    /// @brief  Returns a const pointer to the first item.
    /// @return The first item as a const pointer.
    T* begin() const {
        return mStorage;
    }

    /// @brief  Returns a const pointer to the end.
    /// @return The end as a const pointer.
    T* end() const {
        return &mStorage[mSize];
    }

    SmallVector(const SmallVector &) = delete;
    SmallVector(SmallVector &&) = delete;
    SmallVector &operator = (const SmallVector &) = delete;
    SmallVector &operator = (SmallVector &&) = delete;

private:
    void grow( size_t newCapacity) {
        T* oldStorage = mStorage;
        T* newStorage = new T[newCapacity];

        std::memcpy(newStorage, oldStorage, mSize * sizeof(T));

        mStorage = newStorage;
        mCapacity = newCapacity;

        if (oldStorage != mInplaceStorage) {
            delete [] oldStorage;
        }
    }

    void push_back_and_grow(const T& item) {
        grow(mCapacity + Capacity);

        mStorage[mSize++] = item;
    }

    T* mStorage;
    size_t mSize;
    size_t mCapacity;
    T mInplaceStorage[Capacity];
};

} // end namespace Assimp

#endif // !! AI_SMALLVECTOR_H_INC