VarLenTag.hpp

Go to the documentation of this file.

#ifndef VAR_LEN_TAG_HPP
#define VAR_LEN_TAG_HPP

#include <cstdlib>
#include <cstring>

namespace moab
{

/* Remove this preprocessor macro to compile
 * simple implementation w/ no inlined storage
 */
#define VAR_LEN_TAG_ELIDE_DATA

/* Define class data layout depending on macros:
 * VAR_LEN_TAG_ELIDE_DATA and TEMPLATE_SPECIALIZATION
 */
#ifndef VAR_LEN_TAG_ELIDE_DATA

/* The trivial implementation */
public
VarLenTagData
{
  public:
    struct
    {
        struct
        {
            unsigned size;
            unsigned char* array;
        } mPointer;
    } mData;
};

#elif !defined( MOAB_TEMPLATE_SPECIALIZATION )

/* A little more advanced data structure for VarLenTag.
 * If the amount of tag data is less than or equal to the
 * size of the array pointer, store it inline in the pointer
 * value field so no memory needs to be allocated.
 */
class VarLenTagData
{
  public:
    enum
    {
        INLINE_COUNT = sizeof( unsigned char* )
    };

    union
    {
        struct
        {
            unsigned char* array;
            unsigned size;
        } mPointer;
        struct
        {
            unsigned char array[INLINE_COUNT];
            unsigned size;
        } mInline;
    } mData;
};

#else

/* Most complex implementation.  Same as the previous one, except
 * when storing data inline, also utilize any padding in the struct.
 * This implementation requires support for template specialization.
 *
 * - The data must be first in the struct to avoid alignment issues
 *   for double and 64-bit handle values on some platforms.
 * - The size must therefore be at the end of the struct (including
 *   after any padding) because a) it cannot be at the beginning and
 *   b) it must be at the same location in both structs in the union.
 * - For the mPointer variation, the padding must be declared
 *   explicitly in order for the size to be forced to the end.
 * - Template specialization is used to avoid declaring a
 *   zero-length array for pad on 32-bit platforms.
 *   NOTE: GCC allows zero-length arrays, but Sun's compiler
 *   (and most others) do not.
 */
template < unsigned >
class VarLenTagDataTemplate
{
  public:
    inline VarLenTagDataTemplate() {}

    struct MallocData
    {
        unsigned char* array;
        unsigned size;
    };

    enum
    {
        INLINE_COUNT = sizeof( MallocData ) - sizeof( unsigned )
    };

    union
    {
        struct
        {
            unsigned char* array;
            unsigned char pad[INLINE_COUNT - sizeof( unsigned char* )];
            unsigned size;
        } mPointer;
        struct
        {
            unsigned char array[INLINE_COUNT];
            unsigned size;
        } mInline;
    } mData;
};

template <>
class VarLenTagDataTemplate< 0u >
{
  public:
    inline VarLenTagDataTemplate< 0u >() {}

    enum
    {
        INLINE_COUNT = sizeof( unsigned char* )
    };

    union
    {
        struct
        {
            unsigned char* array;
            unsigned size;
        } mPointer;
        struct
        {
            unsigned char array[INLINE_COUNT];
            unsigned size;
        } mInline;
    } mData;
};

typedef VarLenTagDataTemplate< sizeof( unsigned char* ) - sizeof( unsigned ) > VarLenTagData;

#endif

/**\brief Class for storing variable-length tag data
 *
 * Class for managing variable-length tag data.
 *\NOTE This class must behave as if it were initialized to empty
 *      if it is memset to zero w/out invoking any constructor.
 */
class VarLenTag
{
  protected:
    VarLenTagData mData;

  public:
    inline VarLenTag()
    {
        mData.mData.mPointer.size = 0;
    }
    inline VarLenTag( unsigned size );
    inline ~VarLenTag()
    {
        clear();
    }
    inline VarLenTag( const VarLenTag& copy );
    inline VarLenTag( unsigned size, const void* data );

    inline unsigned size() const
    {
        return mData.mData.mPointer.size;
    }

    inline unsigned char* data()
#ifdef VAR_LEN_TAG_ELIDE_DATA
    {
        return size() <= VarLenTagData::INLINE_COUNT ? mData.mData.mInline.array : mData.mData.mPointer.array;
    }
#else
    {
        return mData.mData.mPointer.array;
    }
#endif

    inline unsigned long mem() const
#ifdef VAR_LEN_TAG_ELIDE_DATA
    {
        return size() <= VarLenTagData::INLINE_COUNT ? 0 : size();
    }
#else
    {
        return size();
    }
#endif

    inline const unsigned char* data() const
    {
        return const_cast< VarLenTag* >( this )->data();
    }

    inline unsigned char* resize( unsigned size );

    inline void clear();

    inline void set( const void* dat, unsigned sz )
    {
        memcpy( resize( sz ), dat, sz );
    }

    inline VarLenTag& operator=( const VarLenTag& other )
    {
        set( other.data(), other.size() );
        return *this;
    }
};

inline unsigned char* VarLenTag::resize( unsigned s )
{
#ifdef VAR_LEN_TAG_ELIDE_DATA
    if( s <= VarLenTagData::INLINE_COUNT )
    {
        if( size() > VarLenTagData::INLINE_COUNT )
        {
            unsigned char* tmp_ptr = mData.mData.mPointer.array;
            memcpy( mData.mData.mInline.array, tmp_ptr, s );
            free( tmp_ptr );
        }
        mData.mData.mInline.size = s;
        return mData.mData.mInline.array;
    }
    else if( size() <= VarLenTagData::INLINE_COUNT )
    {
        void* tmp_ptr = malloc( s );
        memcpy( tmp_ptr, mData.mData.mInline.array, size() );
        mData.mData.mPointer.array = reinterpret_cast< unsigned char* >( tmp_ptr );
    }
    else
#endif
        if( size() < s )
    {
        void* tmp_ptr              = size() ? realloc( mData.mData.mPointer.array, s ) : malloc( s );
        mData.mData.mPointer.array = reinterpret_cast< unsigned char* >( tmp_ptr );
    }
    mData.mData.mPointer.size = s;
    return mData.mData.mPointer.array;
}

inline VarLenTag::VarLenTag( unsigned sz )
{
#ifdef VAR_LEN_TAG_ELIDE_DATA
    if( sz > VarLenTagData::INLINE_COUNT )
#endif
        mData.mData.mPointer.array = reinterpret_cast< unsigned char* >( malloc( sz ) );
    mData.mData.mPointer.size = sz;
}

inline void VarLenTag::clear()
{
#ifdef VAR_LEN_TAG_ELIDE_DATA
    if( size() > VarLenTagData::INLINE_COUNT )
#else
    if( size() )
#endif
        free( mData.mData.mPointer.array );
    mData.mData.mPointer.size = 0;
}

inline VarLenTag::VarLenTag( const VarLenTag& copy ) : mData( copy.mData )
{
#ifdef VAR_LEN_TAG_ELIDE_DATA
    if( size() > VarLenTagData::INLINE_COUNT )
#endif
    {
        mData.mData.mPointer.array = reinterpret_cast< unsigned char* >( malloc( size() ) );
        memcpy( mData.mData.mPointer.array, copy.mData.mData.mPointer.array, size() );
    }
}

inline VarLenTag::VarLenTag( unsigned sz, const void* dat )
{
    mData.mData.mPointer.size = 0;
    if( sz ) memcpy( resize( sz ), dat, sz );
}

}  // namespace moab

#endif