Re: [ros-dev] revision 26772, Mon May 14 03:18:42 2007 UTC

[jimtabor]

Hi!

>   It should probably be
>  + Exp -= (1 - EXCESS);
>  in EFtoF() and
>  + Exp += (1 - EXCESS);
>  in FtoEF(). The other way round.
>
>     
No, this would break compatibility. The way to verify this. Write a 
driver, install it
and send a packet to it, so to activate the test. Have the driver dump 
to WinDbg.
>   Suggestion to make it a little clearer:
>  #define BIAS 127
>  Exp -+= (BIAS - 2); 
I know about the IEEE bias. I'm just using my old 68k code that I'm 
comfortable with. I'll
change this later with the Dc handle stuff I'm still testing.


Thanks,
James

[Timo Kreuzer]

jimtabor schrieb:
>   No, this would break compatibility. The way to verify
> this. Write a
>  driver, install it
>  and send a packet to it, so to activate the test. Have the driver dump 
>  to WinDbg. 
Ok, I take my time to go into this, because I *am* interested in 
compatibility.

Let's analyze how the conversion between FLOAT and EFLOAT works on XP. 
We could simply use some documentation floating around, but let's do it 
on our own, just for the fun. We don't need no 
itchy-bitchy-kmtest-driver-callback-winpooch-hooky-thingy, because 
Windows has already all we need to do this completely in user mode.
DC_ATTR has some EFLOATs and what we need is a function that takes a 
FLOAT and stores it as EFLOAT. SetWorldTransform() seems suitable (In 
fact the values will be stored in the DC_ATTR structure only after a 
following call to GetWorldTransform()). And we need a windows compatible 
structure definition for DC_ATTR, wich we can get from a well known 
book. For the code see attachment.

Now let's see what we get with different parameters for the float:

f: 1.000000 (0x3f800000) -> lMant: 0x40000000, lExp: 0x000002
f: -1.000000 (0xbf800000) -> lMant: 0xc0000000, lExp: 0x000002
f: 2.000000 (0x40000000) -> lMant: 0x40000000, lExp: 0x000003
f: -2.000000 (0xc0000000) -> lMant: 0xc0000000, lExp: 0x000003
f: 1.500000 (0x3fc00000) -> lMant: 0x60000000, lExp: 0x000002
f: -1.500000 (0xbfc00000) -> lMant: 0xa0000000, lExp: 0x000002
f: 1235.000000 (0x449a6000) -> lMant: 0x4d300000, lExp: 0x00000c
f: -1235.000000 (0xc49a6000) -> lMant: 0xb2d00000, lExp: 0x00000c

Looks like Feng Yuan was right.
Now let's see what your code would do with f=1.

FtoEF( EFLOAT_S * efp, FLOATL f)
{

...
 Exp = EXP(worker.l);            // Exp = (((0x3f800000) >> 23L) & 0xFF) = 0x7F
 Mant = MANT(worker.l);  // Mant = ((0x3f800000) & 0x7FFFFFL) = 0x00000

 Mant = ((Mant << 7) | 0x40000000 | SIGN(worker.l)); 
        // Mant = (0 << 7) | 0x40000000 | (0x3f800000 & 0x80000000 )= 0 |
0x40000000 | 0 = 0x40000000
 Exp -= (1 - EXCESS); // Exp = 0x7F - (1-126) = 0x7F + 0x7D = 0xFC

 efp->lMant = Mant;
 efp->lExp = Exp;
...
}

Replace the - by a + and you get

 Exp += (1 - EXCESS); // Exp = 0x7F + (1-126L) = 0x7F - 0x7D = 0x2

Wich is what we have discovered windows does.

And it looks like there's another thing, you didn't take into account. 
Ok, I give you a hint: It has something todo with the sign bit.
You don't get it? Well, it's all there!

Thanks,
Timo





typedef struct _GDI_TABLE_ENTRY
{
	PVOID KernelData; /* Points to the kernel mode structure */
	HANDLE ProcessId; /* process id that created the object, 0 for stock objects */
	LONG Type;        /* the first 16 bit is the object type including the stock obj flag,
the last 16 bits is just the object type */
	PVOID UserData;   /* Points to the user mode structure, usually NULL though */
} GDI_TABLE_ENTRY, *PGDI_TABLE_ENTRY;

typedef PGDI_TABLE_ENTRY (CALLBACK * GDIQUERYPROC) (void);

#define GDI_HANDLE_COUNT 0x10000

#define GDI_HANDLE_INDEX_MASK (GDI_HANDLE_COUNT - 1)

#define GDI_HANDLE_GET_INDEX(h)    \
    (((ULONG_PTR)(h)) & GDI_HANDLE_INDEX_MASK)

typedef union
{
  FLOAT f;
  ULONG l;
} gxf_long;

typedef LONG FIX;

typedef struct _EFLOAT_S
{
    LONG lMant;
    LONG lExp;
} EFLOAT_S;

/* XFORM Structures */
typedef struct _MATRIX_S
{
    EFLOAT_S efM11;
    EFLOAT_S efM12;
    EFLOAT_S efM21;
    EFLOAT_S efM22;
    EFLOAT_S efDx;
    EFLOAT_S efDy;
    FIX fxDx;
    FIX fxDy;
    FLONG flAccel;
} MATRIX_S;

/* Structure definition taken from Feng Yuan's book "Windows Graphics Programming
Win32 GDI and DirectDraw" */
typedef struct
{
	void	*pvLDC;
	DWORD	SomeStuff1[7];
#if _WIN32_WINNT >= 0x0500
	DWORD	SomeStuff2[4];		// 0x20
#endif
	DWORD	SomeStuff3[10];		// 0x030
#if _WIN32_WINNT >= 0x0500
	DWORD	SomeStuff4[8];		// 0x58
#endif
	DWORD	SomeStuff5[7];		// 0x78
	MATRIX_S	mxWorldToDevice;	// 0x94
	MATRIX_S	mxDeviceToWorld;	// 0xD0
	MATRIX_S	mxWorldToPage;		// 0x10C
	// More stuff we don't need
} DC_ATTR, *PDC_ATTR;

[James Tabor]

Hi!
Yes! I will fix it.
Thanks,
James