Thread: Converting C++ inline ASM from GCC to VS

Hi,
I'm attempting to convert an opensource project from GCC to Visual Studio Express C++. I have almost everything compiling, except the inline asm code. I am a beginner in C++, so some of my questions may be "duh!". I have spent time Googling and reading tutorials, and still have not solved all the compile errors.

In GCC C++ inline ASM, the code is contained within

Code:

asm(" ");

In VS C++ it is

Code:

__asm{ }

Then there is the issue of line returns '\n' being required for GCC but apparently not for VS...

So... when using a header '#define' statment that incorporates an asm statement, how should it be converted?

Original:

Code:

#define GOrgueMemset(where, what, howmany) asm("\n\tcld\n\trep\n\tstosl\n" : : "D" (where), "a" (what), "c" (howmany))

Converted?

Code:

#define GOrgueMemset(where, what, howmany) __asm{ tcld trep tstosl : : "D" (where), "a" (what), "c" (howmany)}

But then there is this error:
error C2400: inline assembler syntax error in 'opcode'; found 'trep'
So something in there is not right.

Next issue, another #define from the header, this later gets called from another __asm statement - and I have no clue what to remove.

Code:

#define ASM_DECODE_SU(z) "                    \n\
    movq (%0,%1),%%mm3                         \n\
    addl $8,%1                                             \n\
    movq %%mm3,%%mm1                         \n\
    psubsw %%mm2,%%mm3                     \n\
    movq %%mm1,%%mm2                         \n\
"

Any comments, help, links to read, etc. welcome.

GrahamG
Johannesburg, South Africa

Well you also need to replace all the \t with a tab (or a space)

> tcld trep tstosl
Should be
cld rep stosl

> GOrgueMemset
I have no idea what this is going to achieve over using the normal memset.
Other Builtins - Using the GNU Compiler Collection (GCC)
Given that gcc will inline memset() to begin with, this just seems bone-headed to me.
Start with

Code:

#define GOrgueMemset(where, what, howmany)   memset(where,what,howmany)

The first step would be to figure out the actual C++ code that corresponds to the assembler, then actually try it to see if it works.

Because going on the memset horror, the author has used assembler "because they could" rather than for any good reason.

One thing is for sure, if there is a lot of use of the : syntax in the GCC assembler, then this will be hard to translate literally into VS syntax.

I don't think there is a lot more than what you know already about the asm keyword.
All it tells the compiler to do is copy/paste the text into the output, and hope the assembler can understand it.

The rest is really figuring out what the instructions are all about, and for that you need an op-code list.

This seems like a nice list (to a point)
The Intel 8086 / 8088/ 80186 / 80286 / 80386 / 80486 Instruction Set
but I see that your second snippet seems to use some MMX/SSE instructions (or later...)

Can you post the URL of the project, maybe others here can take a stab at explaining a few bits for you along the way.