Thread: inline asm question

Code:

__asm
     (
         "CLD;"               
         "MOV EAX, color ;"
         "MOV ECX, (SCREEN_WIDTH/2);"  
         "MOV EDI, video_buffer;" 
         "REP STOSD;"
         );

After much searching, I found that the only way to do inline assembly in dev-cpp is to do it like that, but there seems to be a problem with this code (which I didn't write, since I know almost nothing about assembly). The author of the book I reading says this code is equivalent to:

Code:

for (DWORD ecx = 0, DWORD * edi = video_buffer; ecx< (SCREEN_WIDTH/2); ecx++)
   edi[ecx] = color;

But my compiler has problems with his assembly code:

[quote]
c:\windows\TEMP/cclnyggb.s: Assembler messages:
c:\windows\TEMP/cclnyggb.s:647: Error: too many memory references for `mov'
c:\windows\TEMP/cclnyggb.s:647: Error: too many memory references for `mov'
c:\windows\TEMP/cclnyggb.s:647: Error: too many memory references for `mov'
c:\windows\TEMP/cclnyggb.s:647: Error: no such instruction: `STOSD
[/code]

Can any assembly programmers tell me whats wrong?

Difficult question this is....Get back to you, I will....

P.S. It sounds like STOSD is a label. If it is in fact a label, you should probably put a label STOSD at the beginning of your inline asm code.

Looking at my post now, I should probably have inserted the authors comments, but I don't remember what they are...When I get home today I'll add them..maybe that will help.

[edit]
Ok now that I'm finally at home, here's the original code from the book:

Code:

_asm
        {
        CLD                                          ; clear direction of copy to forward
        MOV EAX, color                         ; color goes here
        MOV ECX, (SCREEN_WIDTH/2) ; number of DWORDS goes here
        MOV EDI, video_buffer             ; address of line to move data
        REP STOSD                               ; send the Pentium X on its way...
         }

Well, anyhow if someone can help me out that would be great, but if I have to I'll just use the C++ "version" of the code...I suppose it might compile with MSVC++ but I haven't set it up for direct X as of yet

[/edit]

if your using the bloodshed Dev-C++ compiler, use the following syntax (AT&T style):

%register
$constant value
[memory] reference
l, w, b: operand size specification

operand? source, destination

movb %al, %bl
movw $0x0000, %cx
movl [eax], ebx

I hope this helps you!

if your using the bloodshed Dev-C++ compiler, use the following syntax (AT&T style):

I'm sure that would help me, but since I know practically no asm I fail to understand completely . I got this code from the book I'm reading...Actually I discovered a way to use intel syntax:

Add the following commands when calling compiler
-masm=intel

Well anyways, I entered that a couple days ago and only realized today that I didn't check the box next to it I got rid of those errors I was getting, but now I get linker errors, "Undefined reference to..." with the names of my variables...

I'm basically using bubba's code:

Code:

 asm
         (
         "cld;"
         "les edi, [video_buffer];"
         "mov eax, [color];"
         "mov ecx, [SCREEN_WIDTH];"
         "shr ecx, 1;"
         "rep stosd;"
         );

I'm guessing shr is binary shift right? (>>, or is it << i forget lol)

the code should be as follows

Code:

__asm {
        cld
        mov eax, color
        mov ecx, SCREEN_WIDTH/2
        mov edi, video_buffer
        rep stosd
}

Code:

the code should be as follows

Wth you talking about? Did you not pay attention! I'm using dev-c++ and it wont accept that!

None of that seems to apply since:

A. All my variables, with the exception of SCREEN_WIDTH are declared within the function

B. Color is defined as follows:

Code:

 DWORD color = _RGB16BIT565(0,(index_y >> 3),0);

With _RGB16BIT565:

Code:

#define _RGB16BIT565(r,g,b) ((b & 31) + ((g & 63) << 5) + ((r & 31) << 11))

Edit:

Heres the full part of the function:

Code:

for (int index_y=0; index_y < SCREEN_HEIGHT; index_y++)
     {
     // build color word up
     DWORD color = _RGB16BIT565(0,(index_y >> 3),0);
     // replicate color in upper and lower 16 bits of 32-bit word 
     color = (color) | (color << 16);

     // now color has two pixel in it in 16.16 or RGB.RGB format, use a DWORD
     // or 32-bit copy to move the bytes into the next video line, we'll need
     // inline assembly though...

     // draw next line, use a little inline asm baby!
     asm
         (
         "push edi;"
         "les edi, [video_buffer];"
         "mov eax, [color];"
         "mov ecx, [SCREEN_WIDTH];"
         "shr ecx, 1;"
         "rep stosd;"
         "pop edi;"
         );

         
     // now advance video_buffer to next line
     video_buffer += (ddsd.lPitch >> 1);
     
     }

I guess i should set up dx9 for msvc++ 6...It appears most people who know anything about inline asm don't use dev-c++...go figure

You have to do a few extra things when using gas (gnu assembler) to generate inline code.

You need to declare your variables as static using the "__asm__" keyword so that the assembler 'knows' about them.

Consider the following simple example:

Code:

/*at&t inline assembly for mingw (gas)*/
#include <windows.h>
int main()
{
static char *pTxt __asm__( "pTxt" ) = "Hello World";
static char *pTitle __asm__( "pTitle" ) = "Using inline assembly with gas (MinGW)";

__asm__ 
  (
  "pushl	$0;"
  "pushl	pTitle;"
  "pushl	pTxt;"
  "pushl	$0;"
  "call _MessageBoxA@16;"
  );
return 0;
}

Hope that helps.

ps. - sorry for the AT&T syntax, Bubba.

Well that got it to compile...now it just opens for a sec then closes again...I'm fairly confident its not any of the functions failing and causing the program to end, since I added a message box after each test (which should also play a sound MB_ICONEXCLAMATION) So I'm stumped


I guess as a last resort I'll post the entire code...Although I don't expect anyone to read it...its a bit messy and I just copied and pasted a bunch of message boxes so the text within them wont correspond with the function