Question

Due to optimization reasons I thought about calling directly (with inline assembler)
to the functions “fldl” and “fist”. Sadly I don’t get how to run it since i’m not that god in assembler.

i didn’t get further than this:

double* input;         
long long output;

__asm fldl input;      
__asm fist output;

Answer 1

__asm fld input will actually attempt to read your pointer value as if it were a floating-point value. If you want to read a floating-point value pointed by a pointer, you have to go through a two-step process: read the address into a register and then read the data using the address in the register. On a 32-bit platform it will be something along the lines of

__asm {
  mov eax, input
  fld qword ptr [eax]
  fistp output
}

I just tried it in VS2005 and it works. (Note that as other people stated in the comments, fist does not support storing to 64-bit long long, while fistp does. But you probably need fistp anyway, i.e. a popping store.)