Q39381: BASIC Supports MASM 5.10 Update .MODEL and PROC Extensions

Article: Q39381
Product(s): See article
Version(s): 4.00 4.00b 4.50
Operating System(s): MS-DOS
Keyword(s): ENDUSER | B_BasicCom SR# S881213-30 | mspl13_basic
Last Modified: 21-DEC-1988

The Microsoft Macro Assembler Version 5.10 includes several new
features (not found in MASM Version 5.00 or earlier) that simplify
assembly-language routines linked with high-level language programs
Two of these features are as follows:

1. An extension to the .MODEL directive that automatically sets up
   naming, calling, and return conventions for a given high-level
   language; for example, .MODEL MEDIUM,BASIC

2. A modification of the PROC directive that handles most of the
   procedure entry automatically. The PROC directive saves specified
   registers, defines text macros for passed arguments, and generates
   stack setup code on entry and stack tear-down code on exit.

These new features are supported by QuickBASIC Versions 4.00, 4.00b,
and 4.50 and the Microsoft BASIC Compiler Versions 6.00 and 6.00b.

Section 5 of the "Microsoft Macro Assembler 5.1: 5.1 Update" manual
discusses the new features.

Page 332 of the "Microsoft QuickBASIC Version 4.00: Learning and Using
QuickBASIC" manual provides an example of an assembly-language
function called by BASIC. The example from Page 332 is modified below
to demonstrate the new features in the Microsoft Macro Assembler
Version 5.10.

Compile and Link Instructions are as follows:

   BC power.bas;
   MASM power.asm,powera;
   LINK power + powera;

The following is the BASIC Program, POWER.BAS, which invokes the
assembly language function POWER2:

   DEFINT A-Z
   DECLARE FUNCTION power2 (x%, y%)
   PRINT power2(3, 5)
   END

The following is POWER2.ASM, an example of using the extended .MODEL
and .PROC directives in MASM 5.10:

.model medium,BASIC  ;Adds the language option ",BASIC"
.code
                     ;PUBLIC directive was removed. The label on
                     ;the PROC directive is now the function name.
Power2 PROC arg1:word, arg2:word  ;parameters added to PROC

   ;Note: PUSH BP and MOV BP,SP are no longer needed.
   ;The arguments are refered to by the names supplied on the
   ;PROC list instead of their offset from BP (Base Pointer):
       mov   bx,arg1
       mov   ax,[bx]
       mov   bx,arg2
       mov   cx,[bx]
       shl   ax,cl
   ;Note, POP BP is no longer needed.
       ret      ;RET is used now, instead of RET n, (where n is
                ;two times the number of passed arguments.)
Power2 endp
       end

For comparison, the following is the equivalent, earlier (MASM Version
5.00) form for POWER2.ASM, taken from Page 332 of "Learning and Using
QuickBASIC" (for Versions 4.00 and 4.00b, and BASIC Compiler Versions
6.00 and 6.00b):

.model medium
.code
       PUBLIC Power2
Power2 PROC
       PUSH  BP
       MOV   BP,SP        ; Set stack framepointer
       mov   bx,[bp+8]    ; Load Arg1 into
       mov   ax,[bx]      ;   AX
       mov   bx,[bp+6]    ; Load Arg2 into
       mov   cx,[bx]      ;   CX
       shl   ax,cl        ; AX = AX * (2 to power of CX)
                          ; Leave return value in AX
       POP   BP           ; Exit sequence -- restore old BP
       ret   4            ; Return and restore 4 bytes.
Power2 endp
       end

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