GDI_TABLE_ENTRY structure - Ros-dev

30 Aug 2007

Our current gdi handle and handle table entry code uses a bunch of 
macros, masks, bitshifts and even hardcoded values, iirc.
This leads imo to errors, will make the code less portable and cannot 
make use of better compiler optimizations.
So I have created a new GDI_TABLE_ENTRY struct and a new type GDIHANDLE. 
Both use unions and packed structs to
directly access all fields. GDI_TABLE_ENTRY is completely compatible to 
our current one, so all the code would still be valid.

+ the compiler can optimize access of single elements better (movzx, 
byte ptr ...)
+ no more need for additional masks, shifts and macros
+ no more messed up code because of wrong hardcoded values
+ better readable code
+ probably easier porting to 64 bits

- must be redefined for big-endian systems
- direct access of stockbit is slightly slower, but could still be 
handled by a macro

#pragma pack(push,1)
typedef struct
{
    PVOID KernelData; /* Points to the kernel mode structure */
    union
    {
        DWORD ProcessId; /* process id that created the object, 0 for 
kernel objects */
        struct
        {
            unsigned ProcessId16: 16;
            unsigned Unused: 16;
        };
    };
    union
    {
        ULONG Type;
        struct
        {
            union
            {
                unsigned TypeLower: 16;
                struct
                {
                    union
                    {
                        unsigned HandleTypeStock: 8;
                        struct
                        {
                            unsigned HandleType: 7;
                            unsigned StockBit: 1;
                        };
                    };
                    unsigned ReuseCount: 8;
                };
            };
            union
            {
                unsigned TypeUpper: 16;
                struct
                {
                    unsigned StorageType: 8; /* PEN uses same value as 
BRUSH here, no stock bit */
                    unsigned Flags: 8;
                };
            };
        };
    };
    PVOID UserData;   /* Points to the user mode structure, usually NULL 
though */
} GDI_TABLE_ENTRY, *PGDI_TABLE_ENTRY;;

typedef union
{
    HGDIOBJ Handle;
    struct
    {
        unsigned Index: 16;
        union
        {
            unsigned Upper: 16;
            struct
            {
                union
                {
                    unsigned HandleTypeStock: 8;
                    struct
                    {
                        unsigned HandleType: 7;
                        unsigned StockBit: 1;
                    };
                };
                unsigned ReuseCount: 8;
            };
        };
    };
} GDIHANDLE, *PGDIHANDLE;
#pragma pack(pop)