Article ID: 39520
Article Last Modified on 10/16/2003
APPLIES TO
- Microsoft Macro Assembler 5.1 Standard Edition
- Microsoft Macro Assembler 6.0 Standard Edition
- Microsoft Macro Assembler 6.0a
- Microsoft Macro Assembler 6.0b
This article was previously published under Q39520
SUMMARY
The following MASM program shows how to receive an integer from a C program, then pass the value back to the C program as a double. Note: This routine was composed for the large-memory model and assumes that a coprocessor exists on the system.
MORE INFORMATION
Below is the C program that calls the MASM routine. It should be compiled for large-memory model and either 8087 or emulator-math library.
Also shown is the MASM routine. The main piece to this program is the FILD instruction that transforms the integer to a floating-point real, then pushes the value on the co-processor stack. The other point is to obtain the segment and offset of the __fac variable. A value requiring more than 4 bytes cannot be stored in the DX and AX registers for return, so a double is returned by storing its address in DX:AX.
Sample Code
/* Compile options needed: /AL /FPi87 (or /FPi)
*/
#include <stdio.h>
extern double abc( int x );
void main()
{
int x;
double y;
x = 7;
y = abc( x );
printf( "%The value of y is %lf.\n", y );
}
----------------------------------------------------------------------
; Assemble options needed: /Mx
.MODEL LARGE,C ; so Masm will use C naming conventions
.DATA
.CODE
EXTRN _fac:QWORD ; __fac is the global variable used by C
; for storing floating point accumulations
PUBLIC abc
abc PROC FAR
push bp
mov bp,sp
fild WORD PTR [bp+6]
mov dx,SEG _fac
mov es,dx
fstp QWORD PTR es:_fac ; this pops the value off of
mov ax,OFFSET _fac ; the co-processor and puts it
fwait ; in __fac
mov sp,bp
pop bp
ret
abc ENDP
END
Program Output:
The value of y is 7.000000.
Additional query words: kbinf 5.10 6.00 6.00a 6.00b
Keywords: KB39520
