Question

I need to write a procedure in assembler, that calculates the value of a polynomial.
I have two files:

• C source file
• ASM source file

C file:

#include <stdio.h>
#include <stdlib.h>

double func(double,double);

int main()
{ 
  double x=3;
  double y=2;
  printf("%f\n",func(x,y) );
  return 0;
}

ASM file:

.386
.model flat, c
.stack 100h

.DATA
var DW 27

.code

func PROC a:QWORD, b:QWORD
  finit
  fld b
  fld b
  fmul
  fld b
  fmul
  fld a
  fld a
  fmul
  fld a
  fmul
  mov ax, [var]
  push ax
  fmul
  fdiv
  fwait
  RET
func ENDP

end

What I want to achieve at this stage is value of (b^3) / (27 * a^3).
Probably mov and push are problem’s cause.

As a result I get -1.#IND00

I am on Windows, and using Visual Studio 2012 compiler.
For compilation I use VS2012 command line, and a following bat file:

del *.obj
cl -c poly.c
ml -c poly.asm
cl poly.obj poly.obj

ALSO:

Is there any way to create a procedure with more than 2 arguments?

Answer 1

If you want to load an integer onto the FPU stack you can use fild command. Take also a look for the fimul command, with aid of this you can use a integer constant directly for multiplication.

Please take care about the stack in your implementation. One way to do simply would be

...
fld    qword ptr [b]  
fmul   qword ptr [b]  
fmul   qword ptr [b]  
fild   dword ptr [var]  
fmul   qword ptr [a]  
fmul   qword ptr [a]  
fmul   qword ptr [a]  
fdivp  st(1),st  
...

After the code is done the result will be in st(0).