MORE INFORMATION
See article
51501 for the text of Part 1 of "How to Pass Parameters
Between Basic and Assembly Language." Part 2 is below.
CHAIN AND REFERENCES TO DGROUP
For mixed-language programs that use the CHAIN command, you should
make sure that any code built into an extended (or custom) run-time
module does not contain any references to DGROUP. (The CHAIN command
causes DGROUP to move, but does not update references to DGROUP.) This
rule applies only to mixed-language programs; because Basic routines
never refer to DGROUP, you can ignore this caution for programs
written entirely in Basic.
To avoid this problem, you can use the value of SS or DS, since Basic
always assumes that SS and DS coincide with DGROUP.
CALLING DOS I/O ROUTINES DOES NOT AFFECT QUICKBasic CURSOR POSITION
MASM routines linked with a QuickBasic program that do screen output
(by DOS interrupts) do not update the cursor position after returning
to the calling QuickBasic program. (Note: This also applies to using
CALL INTERRUPT statements in QuickBasic.)
For example, after the following three steps, the next PRINT statement
goes directly after the last QuickBasic PRINT statement, ignoring the
new line position from calling the MASM routine:
- Do a PRINT from QuickBasic.
- CALL a MASM routine that does some DOS display string functions
(INT 21h, function 09H).
- Return to QuickBasic.
This is expected behavior. Assembly-language routines should not
change the Basic cursor position.
SOME COPROCESSOR ASSEMBLER INSTRUCTIONS ARE NOT EMULATED
The Microsoft Macro Assembler version 5.10 does not come with routines
to emulate a math coprocessor.
Page 382 of the "Microsoft Macro Assembler 5.10: Programmer's Guide"
states that to emulate math-coprocessor instructions, you must link
with a Microsoft higher-level language that supports floating-point
emulation of the coprocessor. You would write the assembler procedure
using coprocessor instructions, then assemble with the /E option, and
finally link it with the high-level-language modules. (Note: This is
valid only under DOS; under OS/2, this causes a GP fault.)
However, only a subset of coprocessor instructions is emulated by the
Microsoft high-level languages.
If you link your Microsoft higher-level language to an assembler
routine that invokes an instruction that is NOT emulated by the
higher-level language, then the program gives a run-time error (or
possibly hangs or gives incorrect results) when run on a machine that
has no coprocessor.
Below is a list of the coprocessor (8087 or 80287) instructions that
are not emulated by Microsoft higher-level languages:
Coprocessor
Instruction Definition
----------- ----------
FBLD packed decimal load
FBSTP packed decimal store and pop
FCOS cosine function
FDECSTP decrement stack pointer
FINCSTP increment stack pointer
FINIT initialize processor
FLDENV load environment
FNOP no operation
FPREM1 partial remainder
FRSTOR restore saved state
FSAVE save state
FSETPM set protected mode
FSIN only sine function
FSINCOS sine and cosine function
FSTENV store environment
FUCOM unordered comparison
FUCOMP unordered comparison and pop
FUCOMPP unordered comparison and double pop
FXTRACT extract exponent and significant
Also, some of the no-wait forms of instructions are not emulated, such
as FNSTENV and FNINIT.
APPENDIX B: COMMON PITFALLS
===========================
The following common pitfalls are all explained in more detail in the
main text. This list supplies a simple checklist to go over when you
encounter problems doing mixed-language programming.
- Make certain all registers that need to be saved are preserved.
There are several registers that need to be preserved in a mixed-
language program. These registers are as follows:
CX, BX
BP, SI, DI, SP
CS, DS, SS, ES
- When passing strings to assembly language, watch for two things:
- SADD should be used instead of VARPTR when passing variable-
length strings to assembly language. VARPTR will return the
offset to the string descriptor, not to the string itself.
- The assembly-language routine must not, under any circumstances,
alter the string descriptor in any way.
- When using VARSEG, VARPTR, or SADD to pass addresses to assembly
language, it is important to check the function definition. Since
Basic normally passes all parameters by reference, any parameter
that is an address should be declared using BYVAL. If BYVAL is not
used, Basic will create a temporary variable to hold the address,
then pass a pointer to this variable (in effect, pass a pointer to
a pointer).
- Make certain there is not a label on the END directive in the
assembly-language routine.
- If the routine works outside the environment but doesn't work in a
Quick library, then check to make certain that ES is not assumed to
be equal to DS.
Note: ES and DS should never be assumed to be equal unless the
assembly language routine explicitly sets them equal.
- If updating from QuickBasic version 3.00 or earlier to 4.00 or
later, there are several things to watch for:
- The string descriptor changed between version 3.00 and 4.00 of
QuickBasic. Any assembly-language routines that deal with the
string descriptor should be updated to use the new string
descriptor.
- In QuickBasic versions 3.00 and earlier, it doesn't matter if
some registers are not preserved (such as SI and DI); therefore,
routines that don't preserve these registers will still run.
These registers must be preserved to be used with QuickBasic
versions 4.00 and later.
PASSING NUMERIC VARIABLES FROM
Basic TO ASSEMBLY BY NEAR REFERENCE
===================================
Basic
DECLARE SUB Numint(i%)
DECLARE SUB Numlong(lng&)
DECLARE SUB Numsng(s!)
DECLARE SUB Numdbl(d#)
i% = 2
lng& = 4
s! = 3.4
d# = 5.6
CLS
PRINT " BEFORE","AFTER"
PRINT "Integer: ";i%,,
CALL Numint(i%)
PRINT i%
PRINT "Long : ";HEX$(lng&),,
CALL Numlong(lng&)
PRINT HEX$(lng&)
PRINT "Single : ";s!,
CALL Numsng(s!)
PRINT s!
PRINT USING "Double : ##.#### ";d#,
CALL Numdbl(d#)
PRINT USING "##.####"; d#
END
Assembly
.MODEL MEDIUM, Basic
.CODE
PUBLIC Numint, Numlong, Numsng, Numdbl
Numint PROC
push bp
mov bp, sp ; set stack frame
mov bx, [bp+6]
mov ax, [bx] ; get integer
shl ax, 1 ; multiply by 2
mov [bx], ax ; put new value back
pop bp
ret 2
Numint ENDP
Numlong PROC
push bp
mov bp, sp ; set stack frame
mov bx, [bp+6]
mov cx, [bx] ; get long
mov ax, [bx+2] ; switch high and low words
mov [bx+2], cx ; put new value back
mov [bx], ax
pop bp
ret 2
Numlong ENDP
Numsng PROC
push bp
mov bp, sp ; set stack frame
mov bx, [bp+6]
or BYTE PTR [bx+2], 80h ; set sign bit
pop bp
ret 2
Numsng ENDP
Numdbl PROC
push bp
mov bp, sp ; set stack frame
mov bx, [bp+6]
or BYTE PTR [bx+6], 80h ;set sign bit
pop bp
ret 2
Numdbl ENDP
END
Output
BEFORE AFTER
Integer: 2 4
Long : 4 40000
Single : 3.4 -3.4
Double : 5.6000 -5.6000
PASSING NUMERIC VARIABLES FROM
Basic TO ASSEMBLY BY FAR REFERENCE
==================================
Basic
DECLARE SUB Numint(SEG i%)
DECLARE SUB Numlong(SEG lng&)
DECLARE SUB Numsng(SEG s!)
DECLARE SUB Numdbl(SEG d#)
i% = 2
lng& = 4
s! = 3.4
d# = 5.6
CLS
PRINT " BEFORE","AFTER"
PRINT "Integer: ";i%,,
CALL Numint(i%)
PRINT i%
PRINT "Long : ";HEX$(lng&),,
CALL Numlong(lng&)
PRINT HEX$(lng&)
PRINT "Single : ";s!,
CALL Numsng(s!)
PRINT s!
PRINT USING "Double : ##.#### ";d#,
CALL Numdbl(d#)
PRINT USING "##.####"; d#
END
Assembly
.MODEL MEDIUM, Basic
.CODE
PUBLIC Numint, Numlong, Numsng, Numdbl
Numint PROC
push bp
mov bp, sp ; set stack frame
push es
mov es, [bp+8] ; get seg
mov bx, [bp+6] ; get offset
mov ax, es:[bx] ; get actual integer
shl ax, 1 ; multiply by 2
mov es:[bx], ax ; put back new value
pop es
pop bp
ret 4
Numint ENDP
Numlong PROC
push bp
mov bp, sp ; set stack frame
push es
mov es, [bp+8] ; get seg
mov bx, [bp+6] ; get offset
mov cx, es:[bx] ; get actual long
mov ax, es:[bx+2] ; switch high and low words
mov es:[bx+2], cx ; put back new value
mov es:[bx], ax
pop es
pop bp
ret 4
Numlong ENDP
Numsng PROC
push bp
mov bp, sp ; set stack frame
push es
mov es, [bp+8] ; get seg
mov bx, [bp+6] ; get offset
mov ax, es:[bx+2] ; get actual single
or ah, 80h ; set sign bit
mov es:[bx+2], ax ; put back new value
pop es
pop bp
ret 4
Numsng ENDP
Numdbl PROC
push bp
mov bp, sp ; set stack frame
push es
mov es, [bp+8] ; get seg
mov bx, [bp+6] ; get offset
mov ax, es:[bx+6] ; get actual double
or ah, 80h ; set sign bit
mov es:[bx+6], ax ; put back new value
pop es
pop bp
ret 4
Numdbl ENDP
END
Output
BEFORE AFTER
Integer: 2 4
Long : 4 40000
Single : 3.4 -3.4
Double : 5.6000 -5.6000
PASSING NUMERIC VARIABLES FROM Basic TO ASSEMBLY BY VALUE
=========================================================
Basic
-----
DECLARE SUB ValInt(BYVAL i%)
DECLARE SUB ValLong(BYVAL lng&)
i% = ASC("A")
lng& = ASC("B") * 65536 + ASC("C")
CLS
CALL ValInt(i%)
CALL ValLong(lng&)
END
Assembly
--------
.MODEL MEDIUM, Basic
.CODE
PUBLIC ValInt, ValLong
ValInt PROC
push bp
mov bp, sp ; set stack frame
mov dx, [bp+6] ; get integer
mov ah, 02 ; DOS interrupt to print character
int 21h
pop bp
ret 2
ValInt ENDP
ValLong PROC
push bp
mov bp, sp ; set stack frame
mov dx, [bp+6] ; get first part of long
mov ah, 02 ; DOS interrupt to print character
int 21h
mov dx, [bp+8] ; get second part of long
int 21h ; print it
pop bp
ret 4
ValLong ENDP
END
Output
------
ABC
PASSING NUMERIC VARIABLES FROM ASSEMBLY TO Basic
================================================
Basic
-----
DECLARE SUB AssemSub(dummy AS INTEGER)
CALL AssemSub(dummy%)
END
SUB NumInt(i AS INTEGER)
PRINT "Integer : "; i
END SUB
SUB NumLong(lng AS LONG)
PRINT "Long : "; lng
END SUB
SUB NumSingle(s AS SINGLE)
PRINT "Single : "; s
END SUB
SUB NumDouble(d AS DOUBLE)
PRINT "Double : "; d
END SUB
Assembly
--------
.MODEL MEDIUM, Basic
EXTRN NumInt:PROC ; declare Basic procedures
EXTRN NumLong:PROC
EXTRN NumSingle:PROC
EXTRN NumDouble:PROC
.DATA
intnum dw 32767 ; initialize data
Longnum dd 37999
Singlenum dd 123.45
Doublenum dq 1234.14159
.CODE
PUBLIC AssemSub
AssemSub PROC
push bp
mov bp, sp
mov ax, OFFSET intnum ; get address of integer
push ax
call NumInt
mov ax, OFFSET Longnum ; get address of long
push ax
call NumLong
mov ax, OFFSET Singlenum ; get address of single
push ax
call NumSingle
mov ax, OFFSET Doublenum ; get address of double
push ax
call NumDouble
pop bp
ret 2
AssemSub ENDP
END
Output
------
Integer : 32767
Long : 37999
Single : 123.45
Double : 1234.14159
PASSING A VARIABLE-LENGTH
STRING TO ASSEMBLY BY NEAR REFERENCEP
=====================================
Basic
-----
DECLARE SUB RString(BYVAL soff AS INTEGER)
A$ = "This is the string" + "$" ' "$" terminates string for INT call
CALL RString(SADD(A$))
END
Assembly
--------
.MODEL MEDIUM
.CODE
PUBLIC RString
RString PROC
push bp
mov bp, sp ; set stack frame
mov dx, [bp+6] ; get offset to string
mov ah, 9 ; DOS interrupt to print string
int 21h
pop bp
ret 2
RString ENDP
END
Output
------
This is the string
PASSING A VARIABLE-LENGTH
STRING TO ASSEMBLY BY FAR REFERENCE
===================================
Basic
-----
DECLARE SUB PSTRING(BYVAL STRSEG AS INTEGER, BYVAL STROFF AS INTEGER)
A$ = "Hello World"
PRINT "Before call: ";
PRINT A$
CALL PSTRING(VARSEG(A$), SADD(A$))
PRINT "After call : ";
PRINT A$
Assembly
--------
; Note: This routine uses the MASM 5.10 update PROC extensions
.MODEL MEDIUM, Basic
.CODE
pstring PROC sseg:WORD, soff:WORD
push bx ; save bx register and dx
push dx
push es
mov ax, sseg ; get segment of string
mov es, ax ; put into segment register
; get offset of string
mov bx, soff
; 65 = ASCII 'A'
mov BYTE PTR es:[bx], 65 ; move the 'A' to the first character
; in the string
pop es
pop dx
pop bx ; restore dx and bx
ret
pstring ENDP
END
Output
------
Before call: Hello World
After call : Aello World
PASSING A Basic STRING
DESCRIPTOR TO ASSEMBLY BY NEAR REFERENCE
========================================
Basic
-----
DECLARE SUB RString(A AS STRING)
A$ = "This is the String" + "$" ' "$" terminates the string for INT
call
CALL RString(A$)
END
Assembly
--------
.MODEL MEDIUM, Basic
.CODE
PUBLIC RString
RString PROC
push bp
mov bp, sp ; set stack frame
mov bx, [bp+6] ; get offset of string descriptor
mov dx, [bx+2] ; get address of string
mov ah, 9 ; int call to print string
int 21h
pop bp
ret 2
RString ENDP
END
Output
------
This is the String
PASSING A Basic STRING
DESCRIPTOR TO ASSEMBLY BY FAR REFERENCE
=======================================
Basic
-----
A$ = "This is the String" + "$" ' "$" terminates the string for INT
call
CALLS RString(A$) ' Note: CALLS makes this pass seg and offset
END
Assembly
--------
.MODEL MEDIUM, Basic
.CODE
PUBLIC RString
RString PROC
push bp
mov bp, sp ; set stack frame
push ds
mov ds, [bp+8] ; segment of descriptor
mov bx, [bp+6] ; offset of descriptor
mov dx, [bx+2] ; address of actual string
mov ah, 9 ; DOS interrupt to print string
int 21h
pop ds
pop bp
ret 4
RString ENDP
END
Output
------
This is the String
PASSING A Basic STRING
DESCRIPTOR TO Basic FROM ASSEMBLY
=================================
Basic
-----
DECLARE SUB MkString
CALL MkString
END
SUB BasicSub(TheString AS STRING)
PRINT LEN(TheString)
PRINT TheString
END SUB
Assembly
--------
.MODEL MEDIUM
SType STRUC ; this structure defines a string descriptor
SLength DW 18
Soff DW ?
SType ENDS
.DATA
StringDesc SType <>
TheString DB 'This is the string'
.CODE
EXTRN BasicSub:PROC
PUBLIC MkString
MkString PROC
mov ax, OFFSET TheString ; set up string descriptor
mov bx, OFFSET StringDesc.Soff
mov [bx], ax
mov ax, OFFSET StringDesc.SLength
push ax ; pass address of descriptor to Basic
CALL BasicSub
ret
MkString ENDP
END
Output
------
18
This is the string
PASSING A Basic FIXED-LENGTH
STRING TO AND FROM ASSEMBLY BY NEAR REFERENCE
=============================================
Basic
-----
DECLARE SUB RString(BYVAL offs AS INTEGER)
TYPE fixstring
s AS STRING * 20
END TYPE
DIM a AS STRING * 20
CLS
a = "Basic String$" ' "$" terminates string for assembly
CALL RString(VARPTR(a))
END
SUB BasicSub(a AS fixstring)
LOCATE 2, 1 ' because print in assembly won't move Basic's
PRINT a.s ' screen position
END SUB
Assembly
--------
.MODEL MEDIUM, Basic
EXTRN BasicSub:PROC
.DATA
astr DB 'Assembly String '
.CODE
PUBLIC RString
RString PROC
push bp
mov bp, sp ; set stack frame
mov dx, [bp+6] ; address of string
mov ah, 9 ; DOS interrupt to print string
int 21h
mov ax, OFFSET astr ; address of assembly string
push ax ; pass it to Basic
call BasicSub
pop bp
ret 2
RString ENDP
END
Output
------
Basic String
Assembly String
PASSING A Basic FIXED-LENGTH
STRING TO ASSEMBLY BY FAR REFERENCE
===================================
Basic
-----
DECLARE SUB RString(BYVAL sseg AS INTEGER, BYVAL soff AS INTEGER)
DIM a AS STRING * 20
CLS
a = "Basic String$" ' "$" terminates string for assembly
CALL RString(VARSEG(a), VARPTR(a))
END
Assembly
--------
.MODEL MEDIUM, Basic
.CODE
PUBLIC RString
RString PROC
push bp
mov bp, sp ; set stack frame
push ds
mov ds, [bp+8] ; segment of string
mov dx, [bp+6] ; offset of string
mov ah, 9 ; DOS interrupt to print string
int 21h
pop ds
pop bp
ret 4
RString ENDP
END
Output
------
Basic String
PASSING A USER-DEFINED TYPE FROM
Basic TO ASSEMBLY BY NEAR REFERENCE
===================================
Basic
-----
DEFINT A-Z
TYPE mixed
i AS INTEGER
l AS LONG
s AS SINGLE
d AS DOUBLE
fx AS STRING * 19
END TYPE
DECLARE SUB MasmSub (dummy AS mixed)
DIM dummy AS mixed
CLS
PRINT "Calling assembly routine to fill the user-defined
type."
CALL MasmSub(dummy)
PRINT "Values in user-defined type:"
PRINT "Integer: ", dummy.i
PRINT "Long: ", dummy.l
PRINT "Single: ", dummy.s
PRINT "Double: ", dummy.d
PRINT "fixed-length String: ", dummy.fx
END
Assembly
--------
.MODEL MEDIUM
usrdefType STRUC
iAsm DW 10
lAsm DD 43210
sAsm DD 32.10
dAsm DQ 12345.67
fxAsm DB 'Fixed-length string'
usrdefType ENDS
.DATA
AsmRec usrdefType <>
PUBLIC MasmSub
MasmSub PROC
push bp
mov bp,sp ; set stack frame
push es
push di
push si
push cx
push ds
pop es
mov di,[bp+6] ; get offset of user-defined type
mov si,OFFSET AsmRec ; set up for copy
mov cx,37 ; size of structure
rep movsb ; copy values to Basic variable
pop cx
pop si
pop di
pop es
pop bp
ret 2
MasmSub ENDP
END
Output
------
Integer: 10
Long: 43210
Single: 32.10
Double: 12345.67
fixed-length String: Fixed-length string
PASSING A USER-DEFINED TYPE FROM
Basic TO ASSEMBLY BY FAR REFERENCE
==================================
Basic
-----
DEFINT A-Z
DECLARE SUB MasmSub (BYVAL segment, BYVAL offset)
TYPE mixed
i AS INTEGER
lng AS LONG
s AS SINGLE
d AS DOUBLE
fx AS STRING * 19
END TYPE
DIM dummy AS mixed
CLS
PRINT "Calling assembly routine to fill the user-defined type."
CALL MasmSub(VARSEG(dummy), VARPTR(dummy))
PRINT "Values in user-defined type:"
PRINT "Integer: ", dummy.i
PRINT "Long: ", dummy.lng
PRINT "Single: ", dummy.s
PRINT "Double: ", dummy.d
PRINT "fixed-length String: ", dummy.fx
END
Assembly
--------
.MODEL MEDIUM
usrdefType STRUC
iAsm DW 10
lAsm DD 43210
sAsm DD 32.10
dAsm DQ 12345.67
fxAsm DB 'Fixed-length string'
usrdefType ENDS
.DATA
AsmRec usrdefType <>
PUBLIC MasmSub
MasmSub PROC FAR
push bp
mov bp,sp
push es
push di
push si
push cx
mov es,[bp+8] ; get segment of user-defined type
mov di,[bp+6] ; get offset of user-defined type
mov si,OFFSET AsmRec
mov cx,37 ; size of structure
rep movsb ; copy values to Basic variable
pop cx
pop si
pop di
pop es
pop bp
ret 4
MasmSub ENDP
END
Output
------
Integer: 10
Long: 43210
Single: 32.10
Double 12345.67
fixed-length String: Fixed-length string
PASSING A USER-DEFINED
TYPE FROM ASSEMBLY TO Basic
===========================
Basic
-----
DEFINT A-Z
DECLARE SUB MasmSub
TYPE mixed
i AS INTEGER
lng AS LONG
s AS SINGLE
d AS DOUBLE
fx AS STRING * 19
END TYPE
DIM dummy AS mixed
CLS
PRINT "Calling assembly routine which will fill the";
PRINT " user-defined type."
CALL MasmSub
END
SUB BasicSub (dummy AS mixed)
PRINT "Values in user-defined type:"
PRINT
PRINT "Integer: ", dummy.i
PRINT "Long: ", dummy.lng
PRINT "Single: ", dummy.s
PRINT "Double: ", dummy.d
PRINT "fixed-length String: ", dummy.fx
END SUB
Assembly
--------
.MODEL MEDIUM
usrdefType STRUC
iAsm DW 10
lAsm DD 43210
sAsm DD 32.10
dAsm DQ 12345.67
fxAsm DB 'Fixed-length string'
usrdefType ENDS
EXTRN BasicSub:PROC
.DATA
BasicRec usrdefType <>
.CODE
PUBLIC MasmSub
MasmSub PROC ; no stack frame is needed
; because no arguments are
; passed to assembly
mov ax, OFFSET BasicRec ; get address of structure
push ax ; pass it as argument to Basic
CALL BasicSUb
ret
MasmSub ENDP
END
Output
------
Integer: 10
Long: 43210
Single: 32.10
Double: 12345.67
fixed-length String: Fixed-length string
PASSING AN ARRAY OF
INTEGERS FROM Basic TO ASSEMBLY
===============================
Basic
-----
DEFINT A-Z
DECLARE SUB MasmSub (BYVAL segment, BYVAL offset, BYVAL number)
'REM $DYNAMIC 'Can be either STATIC (the default) or DYNAMIC
DIM x%(1 TO 10) 'Remove comment to define array DYNAMICally
CLS
PRINT "Calling assembly routine to fill array elements..."
CALL MasmSub(VARSEG(x%(1)), VARPTR(x%(1)), 10)
PRINT "Values in array:"
FOR i = 1 TO 10
PRINT x%(i);
NEXT
END
Assembly
--------
.MODEL MEDIUM
.CODE
PUBLIC MasmSub
MasmSub PROC ; can use proc far here too
push bp ; save registers for Basic
mov bp,sp ; get the stack pointer
mov es,[bp+10] ; get segment of array
mov bx,[bp+8] ; get offset of array
mov cx,[bp+6] ; get length of array
mov al,1 ; fill array elements with 1's
next: mov es:[bx],al ; put one in the array element
add bx,2 ; increment counter to next array element
; -- add two bytes for integers, four bytes
; -- for single precision and long integers,
; -- and 8 bytes for double precision numbers
loop next ; loop to assign next array element
pop bp ; restore bp for Basic
ret 6 ; restore stack
MasmSub ENDP
END
Output
------
1 1 1 1 1 1 1 1 1 1
PASSING AN ARRAY OF LONG
INTEGERS FROM Basic TO ASSEMBLY
===============================
Basic
-----
REM Program that calls an assembly routine that fills each
REM element with a 1.
DEFINT A-Z
DECLARE SUB MasmSub (BYVAL segment, BYVAL offset, BYVAL number)
'REM $DYNAMIC 'Can be either STATIC (the default) or DYNAMIC
DIM lng&(1 TO 10) 'Remove comment to define array DYNAMICally
CLS
PRINT "Calling assembly routine to fill array elements..."
CALL MasmSub(VARSEG(lng&(1)), VARPTR(lng&(1)), 10)
PRINT "Values in array:"
FOR i% = 1 TO 10
PRINT lng&(i);
NEXT
END
Assembly
--------
.MODEL MEDIUM
.CODE
PUBLIC MasmSub
MasmSub PROC ; can use proc far here too
push bp ; save registers for Basic
mov bp, sp
mov es, [bp+10] ; get segment of array
mov bx, [bp+8] ; get offset of array
mov cx, [bp+6] ; get length of array
mov al, 1
next: mov es:[bx], al ; put one in the array element
add bx, 4 ; increment counter to next array element
loop next ; loop to assign next array element
pop bp ; restore bp for Basic
ret 6
MasmSub ENDP
END
Output
------
1 1 1 1 1 1 1 1 1 1
PASSING AN ARRAY OF
SINGLE-PRECISION VARIABLES FROM Basic TO ASSEMBLY
=================================================
Basic
-----
REM Program that calls an assembly routine that changes the
REM sign of an array of numbers
DEFINT A-Z
DECLARE SUB MasmSub (BYVAL segment, BYVAL offset, BYVAL number)
'REM $DYNAMIC 'Can be either STATIC (the default) or DYNAMIC
DIM s!(1 TO 10) 'Remove comment to define array DYNAMICally
FOR i% = 1 to 10
s!(i%) = i%
NEXT
CLS
PRINT "Calling assembly routine to fill array elements..."
CALL MasmSub(VARSEG(s!(1)), VARPTR(s!(1)), 10)
PRINT "Values in array:"
FOR i% = 1 TO 10
PRINT s!(i);
NEXT
END
Assembly
--------
.MODEL MEDIUM
.CODE
PUBLIC MasmSub
MasmSub PROC ; can use proc far here too
push bp ; save registers for Basic
mov bp, sp
mov es, [bp+10] ; get segment of array
mov bx, [bp+8] ; get offset of array
add bx, 3 ; offset to byte holding sign bit
mov cx, [bp+6] ; get length of array
mov al, 1
next: or BYTE PTR es:[bx], 80h ; set sign bit
add bx, 4 ; increment counter to next array element
loop next ; loop to assign next array element
pop bp ; restore bp for Basic
ret 6
MasmSub ENDP
END
Output
------
-1 -2 -3 -4 -5 -6 -7 -8 -9 -10
PASSING AN ARRAY OF
DOUBLE-PRECISION VARIABLES FROM Basic TO ASSEMBLY
=================================================
Basic
-----
DECLARE SUB FillDbl(BYVAL ASeg AS INTEGER, BYVAL AOff AS INTEGER)
DIM DblArray(1 TO 5) AS DOUBLE
CALL FillDbl(VARSEG(DblArray(1)), VARPTR(DblArray(1)))
FOR i% = 1 TO 5
PRINT DblArray(i%)
NEXT
END
Assembly
--------
.MODEL MEDIUM, Basic
.DATA
Dbl1 DQ 123.45 ; initialize data table
Dbl2 DQ 456.78
Dbl3 DQ 98765.432
Dbl4 DQ 12345.678
Dbl5 DQ 777.888
.CODE
PUBLIC FillDbl
FillDbl PROC
push bp
mov bp, sp ; set stack frame
push es
push di
push si
mov es, [bp+8] ; segment of array
mov di, [bp+6] ; offset of array
mov si, OFFSET Dbl1 ; get offset of data table
mov cx, 40 ; length of data in table
rep movsb ; copy data table to array
pop si
pop di
pop es
pop bp
ret 4
FillDbl ENDP
END
Output
------
123.45
456.78
98765.432
12345.678
777.888
PASSING AN ARRAY OF Basic STRING DESCRIPTORS TO ASSEMBLY
========================================================
Basic
-----
' This program demonstrates passing an array of strings
' to an assembly language routine. The assembly language
' routine then receives the address of the array, and
' interprets the array as an array of string descriptors.
' It then uses the descriptors to get the length and address
' of the strings. It uses these two values to uppercase all of
' the lowercase alphabetic characters in any of the
' strings, and to skip all others.
' It is very important to pass the assembly routine the number
' of elements in the array.
OPTION BASE 0
DECLARE SUB UpCaseArray (BYVAL ArrayAddress%, arraylen%)
' BYVAL is necessary because we want to pass the VALUE of
' the address, not a pointer to the address.
DIM Num%, Array1$(20)
CLS
WHILE NOT a$ = "quit"
INPUT "Enter a string ('quit' to end): ", a$
Array1$(Num%) = a$
Num% = Num% + 1
WEND
CALL UpCaseArray(VARPTR(Array1$(0)), Num%)
CLS
FOR i% = 0 TO (Num% - 1)
PRINT Array1$(i%)
NEXT
END
Assembly
--------
.MODEL MEDIUM,Basic
.CODE
PUBLIC UpCaseArray
UpCaseArray PROC FAR
push bp
mov bp,sp
push di
mov bx,[bp+6] ; Argument #2: Number of array elements.
mov cx,[bx] ; Get the actual number of array elements.
jcxz EndOutLoop ; If the array has 0 elements then quit.
mov bx,[bp+8] ; Argument #1: Pointer to an array of
; descriptors.
OutLoop: ; CX is the outer-OutLoop counter.
push cx ; Save the outer loop counter.
mov cx,[bx] ; Get the first two bytes of the current
; descriptor, which is the string length.
jcxz EndInLoop ; If zero length, end the inner loop.
mov di,[bx+2] ; The second 2 bytes is the address.
; DI = pointer to current string.
InLoop: ; Check if the char needs to be uppercased.
cmp byte ptr [di],'a' ; Is it < a ?
jb I1 ; If so, then move to the next char.
cmp byte ptr [di],'z' ; Is is > z ?
ja I1 ; If so, then move on to the next char.
and byte ptr [di],05Fh ; Make upper case. Mask -> (0101 1111).
I1: inc di ; Move on to next character in the
; string.
loop InLoop ; Do it for all characters
; (until CX = 0).
; Note: 'loop' decrements CX.
EndInLoop:
add bx,4 ; Move on to next descriptor.
pop cx ; Restore the outer loop counter.
loop OutLoop ; Do for all descriptors
; (until CX = 0).
EndOutLoop:
pop di
pop bp
ret 4
UpCaseArray ENDP
END
Output
------
Enter a string ('quit' to end): First String
Enter a string ('quit' to end): Second String
Enter a string ('quit' to end): quit
FIRST STRING
SECOND STRING
PASSING DYNAMIC ARRAYS OF FIXED-LENGTH STRINGS TO ASSEMBLY
==========================================================
Basic
-----
REM $DYNAMIC
DECLARE SUB Masm (
BYVAL StrLength AS INTEGER,_
BYVAL Length AS INTEGER,_
BYVAL SegAddr1 AS INTEGER,_
BYVAL Addr1 AS INTEGER,_
BYVAL SegAddr2 AS INTEGER,_
BYVAL Addr2 AS INTEGER)
CONST Size% = 3% 'Size of the array (# of elements)
CONST StrSize% = 11% 'Size of strings stored in array
CLS
DIM inArray(1 TO Size%) AS STRING * StrSize%
DIM outArray(1 TO Size%) AS STRING * StrSize%
'Load inArray with a 11 character string " *inArray* ":
FOR i = 1 TO Size%
inArray(i) = " *inArray* "
NEXT i
' Masm will copy the contents of inArray to outArray:
CALL Masm(StrSize%,_
Size%,_
VARSEG(inArray(1)),_
VARPTR(inArray(1)),_
VARSEG(outArray(1)),_
VARPTR(outArray(1)))
' Print the inArray:
PRINT
PRINT
PRINT "inArray: "
FOR i = 1 TO Size%
PRINT inArray(i);
NEXT i
' Print the outArray to see that the contents of inArray
' were copied to it:
PRINT
PRINT "outArray: "
FOR i = 1 TO Size%
PRINT outArray(i);
NEXT i
END
Assembly
--------
;***********************************************************
; The routine 'Masm' copies a dynamic string array of any
; length to another string array.
; Warnings:
; -- Arrays must be adequately dimensioned.
; Masm takes six parameters from the Basic routine:
; 1 - Size of strings in array to be copied (BX)
; 2 - # of elements in array
; 3 - Segment of source array
; 4 - Offset of first element of source array
; 5 - Segment of destination array
; 6 - Offset of first element of destination array
;***********************************************************
.MODEL MEDIUM
.CODE
PUBLIC Masm
Masm PROC
push bp
mov bp, sp
push si
mov bx, [bp+16] ; Size of strings in array -> bx
mov ax, [bp+14] ; Elements in array -> ax
mul bx ; multiply ax by bx and put answer in ax
mov cx, ax ; Number of bytes in array -> cx
mov es, [bp+12] ; Segment of first array (inArray)
mov bx, [bp+10] ; Offset of first element in first
; array
; body
mov si, 0 ; initialize first array index (inArray)
again:
mov al, es:[bx] ; Load byte to copy to second array
; in al
push bx ; save bx
push es ; save es
mov es, [bp+8] ; Segment of second array (outArray)
mov bx, [bp+6] ; Offset of second arrays first
; element
add bx, si ; Get correct offset into 2nd array from
; index
mov es:[bx], al ; Move the byte into the second array
pop es ; restore es
pop bx ; restore bx
add bx, 1 ; point to next element in first array
; (inArray)
add si, 1 ; increment second array (outArray) index
loop again ; Loop until cx is 0
pop si
pop bp
ret
Masm ENDP
END
Output
------
*InArray*
*InArray*
*InArray*
PASSING A TWO-DIMENSIONAL
INTEGER ARRAY FROM Basic TO ASSEMBLY
====================================
Basic
-----
DECLARE SUB TwoInt(BYVAL ASeg AS INTEGER, BYVAL AOff AS INTEGER)
DIM IntArray(1 TO 2, 1 TO 3) AS INTEGER
CALL TwoInt(VARSEG(IntArray(1, 1)), VARPTR(IntArray(1, 1)))
FOR row% = 1 TO 2
FOR col% = 1 TO 3
PRINT IntArray(row%, col%)
NEXT
NEXT
END
Assembly
--------
.MODEL MEDIUM, Basic
.DATA
i11 DW 11 ; initialize data table
i21 DW 21
i12 DW 12
i22 DW 22
i13 DW 13
i23 DW 23
.CODE
PUBLIC TwoInt
TwoInt PROC
push bp
mov bp, sp ; set stack frame
push es
push si
push di
mov es, [bp+8] ; segment of array
mov di, [bp+6] ; offset of array
mov si, OFFSET i11
mov cx, 6 ; number of items to copy
rep movsw ; copy data to array
pop di
pop si
pop es
pop bp
ret 4
TwoInt ENDP
END
Output
------
11
12
13
21
22
23
PASSING A TWO-DIMENSIONAL
FIXED-LENGTH STRING ARRAY FROM Basic TO ASSEMBLY
================================================
Basic
-----
DECLARE SUB TwoFix(BYVAL ASeg AS INTEGER, BYVAL AOff AS INTEGER)
DIM FixArray(1 TO 2, 1 TO 3) AS STRING * 9
CALL TwoFix(VARSEG(FixArray(1, 1)), VARPTR(FixArray(1, 1)))
FOR row% = 1 TO 2
FOR col% = 1 TO 3
PRINT FixArray(row%, col%)
NEXT
NEXT
END
Assembly
--------
.MODEL MEDIUM, Basic
.DATA
Fix11 DB 'String 11' ; allocate string data
Fix21 DB 'String 21'
Fix12 DB 'String 12'
Fix22 DB 'String 22'
Fix13 DB 'String 13'
Fix23 DB 'String 23'
.CODE
PUBLIC TwoFix
TwoFix PROC
push bp
mov bp, sp ; set stack frame
push es
push si
push di
mov es, [bp+8] ; segment of string array
mov di, [bp+6] ; offset of string array
mov si, OFFSET Fix11 ; get offset to string data
mov cx, 54 ; length of all string data
rep movsw ; copy string data to array
pop di
pop si
pop es
pop bp
ret 4
TwoFix ENDP
END
Output
------
String 11
String 12
String 13
String 21
String 22
String 23
PASSING A COMMON BLOCK FROM Basic TO ASSEMBLY
=============================================
Basic
-----
DECLARE SUB PutInfo ()
DIM b%(100)
COMMON /BNAME/ a%, b%(), c%
CALL PutInfo
CLS
PRINT a%, c%
FOR i = 0 TO 100
PRINT b%(i);
NEXT i
END
Assembly
--------
.MODEL MEDIUM
BNAME segment COMMON 'BC_VARS'
a dw 1 dup (?)
b db 202 dup (?) ;Note that all the space for the
;array is set up
c dw 1 dup (?)
BNAME ends
DGROUP group BNAME
.CODE
PUBLIC PutInfo
PutInfo PROC FAR
push bp
mov bp, sp ; set stack frame
push di
inc word ptr dgroup:a ; add 1 to a
inc word ptr dgroup:c ; add 1 to b
mov cx, 101 ; value to initialize b% array
mov di, offset dgroup:b
repeat:
mov [di], cx ; store value to b% array
add di, 2 ; go to next integer variable
loop repeat ; note value in cx decremented
pop di
pop bp
ret
PutInfo ENDP
END
Output
------
1 2
101 100 99 98 97 96 95 94 93 92 91 90 89 88 87 86 85 84 83 82 81
80 79 78 77 76 75 74 73 72 71 70 69 68 67 66 65 64 63 62 61 60 59
58 57 56 55 54 53 52 51 50 49 48 47 46 45 44 43 42 41 40 39 38 37
36 35 34 33 32 31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15
14 13 12 11 10 9 8 7 6 5 4 3 2 1
Note: When dynamic arrays are used, the array is not placed in
the COMMON block. Instead, a multibyte array descriptor is
placed in the COMMON block. The dynamic array descriptor changes
from version to version, and is not released by Microsoft -- it
is considered Microsoft proprietary information.
AN ASSEMBLY FUNCTION RETURNING AN INTEGER TO Basic
==================================================
Basic
-----
DECLARE FUNCTION qprint%
FOR i = 1 TO 10
x% = qprint%
PRINT x%
NEXT i
Assembly
--------
.MODEL MEDIUM
.DATA
shortnum dw 12345
.CODE
PUBLIC QPrint
QPrint PROC FAR
push BP
mov ax, shortnum ; value is stored in AX
pop BP
ret
QPrint ENDP
END
Output
------
12345
12345
12345
12345
12345
12345
12345
12345
12345
12345
AN ASSEMBLY FUNCTION RETURNING A LONG INTEGER TO Basic
======================================================
Basic
-----
DECLARE FUNCTION qprint&
FOR i = 1 TO 10
x& = qprint&
PRINT x&
NEXT i
Assembly
--------
.MODEL MEDIUM
.DATA
longnum dd 12345
.CODE
PUBLIC QPrint
QPrint PROC FAR
push bp
mov ax, WORD PTR longnum ; high order portion in AX
mov dx, WORD PTR longnum+2 ; low order portion in DX
pop bp
ret
QPrint ENDP
END
Output
------
12345
12345
12345
12345
12345
12345
12345
12345
12345
12345
AN ASSEMBLY FUNCTION RETURNING
A SINGLE-PRECISION VARIABLE TO Basic
====================================
Basic
-----
DECLARE FUNCTION qprint!
FOR i = 1 TO 2
x! = qprint!
PRINT x!
NEXT i
Assembly
--------
.MODEL MEDIUM
.DATA
singlenum DD 98.6
.CODE
PUBLIC QPrint
QPrint PROC FAR
push bp
mov bp, sp
push es
push si
push di
push ds ; set es = ds
pop es
mov si, offset dgroup:singlenum
mov di, [bp+6] ;LOAD VALUE INTO ADDRESS AT BP+6
mov cx, 4
rep movsb
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
Output
------
98.6
98.6
AN ASSEMBLY FUNCTION RETURNING
A DOUBLE-PRECISION VARIABLE TO Basic
====================================
Basic
-----
DECLARE FUNCTION qprint#
FOR i = 1 TO 2
x# = qprint#
PRINT x#
NEXT i
Assembly
--------
.MODEL MEDIUM
.DATA
doublenum DQ 6765.89
.CODE
PUBLIC QPrint
QPrint PROC FAR
push bp
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
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
Output
------
6765.89
6765.89
AN ASSEMBLY FUNCTION RETURNING
A VARIABLE-LENGTH STRING TO Basic
=================================
Basic
-----
DECLARE FUNCTION Qprint$ (i%)
CLS
FOR i% = 1 TO 3
d$ = Qprint$(i%) ' i% is the length of the string to be created.
PRINT d$, LEN(d$)
NEXT
Assembly
--------
.MODEL MEDIUM
.DATA
str db 10 dup (?) ;my own string
mystring dw ? ;my own descriptor (length)
dw ? ;(offset)
.CODE
PUBLIC QPrint
QPrint PROC FAR
push bp ;save registers for Basic
mov bp, sp
push ds
push es
mov bx, [bp+6] ;get the length off the stack
mov cx, [bx] ;and put it in CX
push ds
pop es
mov di, offset dgroup:str ;load the offset into DI
mov ax, 'a' ; load character to fill
rep stosb ;store "a" into the string
mov cx, [bx]
mov bx, offset dgroup:mystring ;put offset of descriptor in
; BX
mov [bx], cx ;length in first two bytes
mov [bx+2], offset dgroup:str ;offset into second two bytes
move ax, bx ;load address of descriptor
; into AX
pop es
pop ds
pop bp ;restore BP for Basic
ret 2 ;return skipping the passed parameters
QPrint ENDP
END
Output
------
a 1
aa 2
aaa 3
USING SETMEM TO ALLOCATE SPACE
FOR MEMORY ALLOCATION IN ASSEMBLY
=================================
Basic
-----
DECLARE SUB AMem(BYVAL AllocSize AS INTEGER)
CLS
' Decrease the size of the far heap so AMem can use a DOS
' interrupt to get dynamic memory
BeforeCall% = SETMEM(-2048)
CALL AMem(1024%)
' Return the memory to the far heap; use a larger value so
' all space goes back into the heap.
AfterCall% = SETMEM(3500)
LOCATE 2, 1
IF AfterCall% <= BeforeCall% THEN
PRINT "Memory not reallocated"
ELSE
PRINT "Memory was successfully reallocated"
END IF
END
Assembly
--------
MODEL MEDIUM, Basic
.DATA
Fail DB 'Failed to allocate memory$'
Success DB 'Successfully allocated memory$'
.CODE
PUBLIC AMem
AMem PROC
push bp
mov bp, sp ; set stack frame
push cx
push es
mov ax, [bp+6] ; get number of bytes free
mov cl, 4 ; divide by 16 to get number of
shr ax, cl ; paragraphs of memory
mov bx, ax
mov ah, 48h
int 21h ; DOS interrupt to allocate block
mov es, ax ; of memory
mov ah, 9
jnc NoFail ; carry flag clear if successful
mov dx, OFFSET Fail ; display failed message
int 21h
jmp Exit ; go back to Basic
NoFail: mov dx, OFFSET Success ; display success message
int 21h
mov ah, 49h
int 21h
Exit: pop es
pop cx
pop bp
ret 2
AMem ENDP
END
Output
Successfully allocated memory
Memory was successfully reallocated