Q64107: Sample Assembly Function Returning Double to BASIC

Article: Q64107
Product(s): See article
Version(s): 4.00 4.00b 4.50
Operating System(s): MS-DOS
Keyword(s): ENDUSER | H_MASM S_QUICKASM B_BasicCom SR# S900718-40 | mspl13_basic
Last Modified: 13-AUG-1990

The two programs shown below demonstrate how an assembly language
function can return a double-precision number to a Microsoft BASIC
program.

This information about interlanguage calling applies to QuickBASIC
versions 4.00, 4.00b, and 4.50 for MS-DOS, to Microsoft BASIC Compiler
versions 6.00 and 6.00b for MS-DOS and MS OS/2, and to Microsoft BASIC
Professional Development System (PDS) versions 7.00 and 7.10 for
MS-DOS and MS OS/2.

For more information about passing other types of parameters between
BASIC and MASM, query in the Software/Data Library for the following
word:

   BAS2MASM

Code Example
------------

The following BASIC program is DFUNC.BAS, which displays a
double-precision number returned from an assembly language function:

   DECLARE FUNCTION QPrint#
   FOR i% = 1 to 2
      PRINT QPrint#
   NEXT

The following program is ADBL.ASM, which will return a
double-precision number when called:

; The following handy .MODEL MEDIUM,BASIC directive is found in MASM
; 5.10 but not in earlier versions:
.MODEL MEDIUM, BASIC
.DATA
        doublenum dq 6765.89

.CODE
        PUBLIC QPrint
QPrint  PROC
        mov bp, sp
        push es
        push si
        push di

        push ds          ; set es = ds
        pop es

        mov si, offset dgroup:doublenum
        mov di, [bp+6]   ; load value into address at bp+6
        mov cx, 4
        rep movsw        ; 4 words at 2 bytes = 8 bytes

        mov ax, [bp+6]   ; load offset of temp value in ax and
        mov dx, ss       ;   ss into dx

        pop di
        pop si
        pop es
        pop bp

        ret 2
QPrint  ENDP
        END

To demonstrate these programs from an .EXE program, compile and link
as follows:

   BC DFUNC.BAS;
   MASM ADBL.ASM;
   LINK DFUNC ADBL;

DFUNC.EXE produces the following output:

   6765.89
   6765.89

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