Question

For the below code, if i want to convert the for loop to in-line assembly, how would it be done?
(Pardon the weird code, i just made it up.)

1) This is for the x86, using visual studio

2) This is a “how to use in line assembly” question, not a “how to optimize this code” question

3) Any other example will be fine. I will think of some better example code in abit.

OK i hope this is a better example:

int doSomething(double a, double b, double c)
{
    double d;
    for(int i=100;i<200;i++)
    {
        d = a*a + b*b + c*c;
        if(d>i)
            return (i-99);
    }
    return -1;
}

Answer 1

It would probably start out something like this incomplete and somewhat inefficient example. Should demonstrate the syntax, though.

double doSomething(void) {
    double a=1,b=2,c=3;
    __asm {
        mov ecx,10
loop:
        fld a // a
        fmul st(0),st(0) // aa
        fld b // b aa
        fmul st(0),st(0) // bb aa
        fsubp // aa-bb
        fstp c // c = a*a-b*b

        // and so on

        dec ecx
        jnz loop
    }
    return a+b+c;
}

Using SSE instructions would be another option.

The VC++ inline assembler is documented here: http://msdn.microsoft.com/en-us/library/4ks26t93.aspx

The Intel processor reference manuals are here: http://www.intel.com/products/processor/manuals/