asm to __asm

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I have a code written in pure C that uses the __asm__ keyword. I need to translate the assembly statements from something the gcc recognises into something the Visual C++ compiler will recognise. In Microsoft's C++ compiler, assembly instructions are invoked using the __asm keyword (not __asm__) and the instructions should be enclosed in curly braces {} not parentheses.
I'm not an assembler coder, please help :)

Here is the code I need to translate to Visual C++ :

#    define FASTDIV(a,b) \
    ({\
        int ret,dmy;\
        __asm__ volatile(\
            "mull %3"\
            :"=d"(ret),"=a"(dmy)\
            :"1"(a),"g"(ff_inverse[b])\
            );\
        ret;\
    })

#define MASK_ABS(mask, level)\
            __asm__ volatile(\
                "cltd                   \n\t"\
                "xorl %1, %0            \n\t"\
                "subl %1, %0            \n\t"\
                : "+a" (level), "=&d" (mask)\
            );

uint32_t a, d;
__asm__ volatile("rdtsc\n\t" : "=a" (a), "=d" (d));
return ((uint64_t)d << 32) + a;

I'm sure it will be an easy answer for someone who has more experience in assembly coding. Thanks in advance!

Posted 6-Oct-10 23:08pm

sirryan

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Aescleal · Answer 1 · 2010-10-07T01:47:00

Confused of England here, how can you have "pure C" with things written in assembler?

The first thing I'd suggest doing is binning the assembler entirely and letting the compiler generate the code. For example the second one looks like a xor and subtract abs function. VC++ implements abs using exactly the same instruction stream (if I've got the slightly bent gcc assembler syntax correct).

Cheers,

Ash

PS: Whenever you see inline assembler in a piece of code try rewriting it in C. For micro-optimisations like that the compiler can often do as good a job as a human programmer. So make sure what you're using is better than the compiler generated code.

PPS: One interesting fact is that hand optimised assembly injected in a compiler's code stream usually turns off the compiler's optimiser so the generated code is often slower. I saw this a couple (er, 10 actually) years ago when an "optimised" strcpy was actually 20% slower than the compilers. While the copy was optimised everything that used it wasn't. How I would have laughed had I not been the programmer.

sirryan · Answer 2 · 2010-10-07T05:17:00

Solution 2

I know that but unfortunately this code is not mine. That is why it is in such condition. I really need this code so I can use it in MSVC environment.

Looking forward for an answer that contains MSVC code. :)

Posted 7-Oct-10 5:17am

sirryan

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Aescleal 8-Oct-10 4:11am

- Don't answer your own questions
- Just rewrite the code in C, it'll be as fast and actually readable

The only (vaguely) tricky one but a quick google for rdtsc and C++ sorts that one out.

__asm__ to __asm