cleaner assembly function ...

Hi,

I have written a fast(? maybe it is possible to do faster...)
inline-assembly-function to rotate an image-plane by 180 degrees.

currently it looks like this (the example code is not too good in
explaining the real problem I have, see below):

----[CODE]-------------------------------------------------------------

void Rotate180Image420p ( uint8_t* dImg[3],
                         uint8_t* sImg[3],
                         int w,
                         int h )
{
    static uint32_t width;
    static uint32_t height;
    static uint8_t* Src;
    static uint8_t* Dst;
    
    Dst = dImg[0];
    Src = sImg[0]+w*h-1;
    width = w;
    height = h;
    
    asm(
        "                            \n\t" /* fast 180 degr. rotate  */
        ".intel_syntax noprefix      \n\t" /* ---------------------- */
        "                            \n\t"
        "pusha                       \n\t" /* safe register state    */
        "                            \n\t"
        "mov    eax,%[width]         \n\t" /* setup registers        */
        "mov    ebx,%[height]        \n\t"
        "mul    ebx                  \n\t"
        "mov    ecx,eax              \n\t"
        "mov    edi,%[dImg]          \n\t"
        "mov    esi,%[sImg]          \n\t"
        "                            \n\t"
        "FLIP_LOOP_Y:                \n\t"
        "                            \n\t"
        "mov    byte ptr dl,[esi]    \n\t" /* copy data ...          */
        "mov    byte ptr [edi],dl    \n\t"
        "                            \n\t"
        "dec    esi                  \n\t"
        "inc    edi                  \n\t"
        "                            \n\t"
        "loop   FLIP_LOOP_Y          \n\t"
        "                            \n\t"
        "popa                        \n\t" /* restore register state */
        "                            \n\t"
        ".att_syntax prefix          \n\t"
        "                            \n\t"
        :
        : 
        [width]  "m" (width),
        [height] "m" (height),
        [dImg]   "m" (Dst),
        [sImg]   "m" (Src)
        );
};

----[/CODE]-------------------------------------------------------------

Well, what I do not like is that clumsy stuff with the static variables.
For this short example I could have done it without them, but if the
parameter-list gets longer...

asm volatile ( ...
	:
	:
        [width]  "m" (width),
        [height] "m" (height),
        [dImg]   "m" (Dst),
        [sImg]   "m" (Src)
	[xdat]   "m" (XOffsetTable),
        [ydat]   "m" (YOffsetTable),
	[zdat]   "m" (ZOffsetTable)
);

... and I try it without that static-variables-hack, GCC/GAS runs out of
registers. And that contrary to the fact that each of the variables I
want access to, *can* be reached somewhere in memory (checked by looking
at the .s-file produced).

Same question formulated different (because I am not sure if I could
really make it clear from the above...): Is there a way to explicitly
tell GCC/GAS to use a memory representation of a variable? "m" does not
enforce it, it just allows for it... and so GCC keeps trying to use
registers (which makes sense with just a few variables), but when using
more variables than there are available registers is completely
pointless... But GCC tries nonetheless and fails without even trying to
use the available memory-pointer.

cu
Stefan

-------------------------------------------------------------------------
This SF.net email is sponsored by: Microsoft
Defy all challenges. Microsoft(R) Visual Studio 2008.
http://clk.atdmt.com/MRT/go/vse0120000070mrt/direct/01/

_______________________________________________
Mjpeg-developer mailing list
[email protected]
https://lists.sourceforge.net/lists/listinfo/mjpeg-developer

-----BEGIN PGP SIGNATURE-----
Version: GnuPG v1.4.6 (GNU/Linux)

iD8DBQBHrCUUYAr+TNUy5vARAtKHAJsHXLRXJ8a2wTGXTHnj7TgUDUY8owCfUEGA
wJQ+Uc3xo4EO02rd3ud4sUs=
=hQmG
-----END PGP SIGNATURE-----