The 640 MEG Shareware Studio 2/The 640 Meg Shareware Studio CD-ROM Volume II (Data Express)(1993).ISO/basic/qbredir.zip/QBREDIR.ASM

Assembly Source File | 1992-03-02 | 18KB | 434 lines

;                Quick Basic Redirected File Display
;
;
;    ----   A modified version of the original PD program REDVIEW.ASM   ----
;        by Alexandr Novy and Peter Horak of Prague, Czechoslovakia
;
;
;    ----   This Public Domain Adaptation for QuickBasic Written By:
;
;                Peter R. Barnes
;            Brentwood, TN
;                       March, 1992
;
;
;    ----   To assemble the object module with TASM, use the command:
;
;                   TASM QBREDIR   ;I don't have MASM,
;                                  ;but I'm sure the
;                                  ;syntax is the same
;
;
;    ----   To use in a QuickBasic program, compile your program
;           and link the module to your code, for example:
;
;                   BC /options YOURPROG;       ;any options you want
;
;                   LINK /linkoptions YOURPROG + QBREDIR;
;
;
;
;    ----   To call the routines in your program, use the following:
;
;                   CALL QFRedSet (FlagIntegerVariable%)
;
;                   CALL QFRedOff
;
;
;    --- IMPORTANT: READ THE QBREDIR.DOC FILE TO SEE HOW TO
;                   PROPERLY USE THESE ROUTINES!!  THE ROUTINES
;                   INSTALL A CUSTOM INTERRUPT HANDLER WHICH
;                   MUST BE TREATED WITH CARE!!
;
;    ----     NOTE: CANNOT BE USED IN THE QB ENVIRONMENT (SEE
;                   QBREDIR.DOC)
;
;
;    ----   I have  added some comments to help explain the code as
;           it applies to QuickBasic, just for general (and my own)
;           reference.  Some of the stuff is pretty elementary, so if
;           you are an assembly language wiz, just skip it; it's there
;           for the rest of us.
;
;
;********************************************************************
;********************************************************************
;
; Make our procedure names available to external programs
;
public QFRedSet, QFRedOff
;
;
;********************************************************************
;
; All Basic modules are assembled using the Medium
; memory model, so we must add the proper assembler directives
;
;
.MODEL Medium, Basic               ;always, for QuickBasic
;
.CODE                              ;make the code segment our default
;
;
;
; We will let QBasic and TASM set the type of procedure, and we will
; declare the module using the TASM simplified format
;
;
QFRedSet proc  uses si di es ds
               ARG flag:PTR = ARGLEN
;
;
; That tells TASM to add code for a Basic procedure call, save
; si,di,es,ds pointers, and that we are passing to the procedure a
; two-byte pointer to the INTEGER (notice that I capitalized that --
; three guesses why) variable /flag/, consisting of ARGLEN number of
; bytes -- the QuickBasic 'call' automatically pushes that address onto
; the stack and TASM calculates the correct offset to those stack
; bytes when it assembles the code. All parameter addresses passed by
; QuickBasic are near references (offset only, 1 word or 2 bytes)
; unless you use the keyword SEG for the passed variable, which tells
; QuickBasic to pass the address as a far reference (segment:offset,
; 2 words or 4 bytes).
;                            ---------
; TASM knows from our 'Basic' directive that the variable we pass will
; be a 2-byte address, and that Basic always makes far calls, leaving a full,
; 2-word return address as the last 4 bytes on the stack; the variable
; address, next on the stack, will be at [B(ase)P(ointer)+6] from the
; present BP value (+ because the stack grows downward in memory).
; That's also how TASM knows that we need a far return, not a near
; return, and also how many bytes to discard, after it pops that QB
; return address, to restore the stack after the procedure ends --
; i.e. 2 bytes for the variable near address...
;
;        push  bp                 ;TASM automatically
;        mov   bp,sp              ;adds the code to save the B(ase)
;                                 ;P(ointer) to the stack in the stack
;                                 ;segment, and set up a new stack
;                                 ;that starts at the end of the old
;                                 ;one pointed to by the current
;                                 ;S(tack)P(ointer) -- i.e.
                                  ;   New bp = Old bp + sp
;                                 ;Actually, our new stack will begin
;                                 ;at New bp + sp, but this will keep
;                                 ;us away from the old stack for
;                                 ;all values of sp, in case sp gets
;                                 ;set to a lower value -- we will
;                                 ;never get lower than the new bp.
;                                 ;Of course, we have to be careful
;                                 ;to preserve that sp value in our
;                                 ;code by always 'popping' the same
;                                 ;number of bytes that we 'push'
;                                 ;onto the stack.
;
;
;                                 ;This is the code that is added
;                                 ;by TASM when it sees the 'Basic'
;         push  si                ;and the 'uses' directives, so we
;         push  di                ;don't need the explicit statements.
;         push  es                ;The address of /flag/ is placed on
;         push  ds                ;the stack first, and ARGLEN tells
;                                 ;TASM how many bytes to discard, when
;                                 ;we return from the call, to get
;                                 ;back to the original stack before
;                                 ;the call.
;
;
;********************************************************************
;
;
;
; The first thing we do is grab and save the address of the QB variable
; that was passed to us, on the stack, by QuickBasic when it made the
; call; remember that TASM knows that [flag] means [BP+6]. In this
; call, we passed the 2-byte offset address of the variable in the
; ds data segment, so the 'word ptr [flag]' will have the 2-byte word
; for the offset moved into ax; then the 2-byte word for the ds data
; segment, whatever it is, will be stored. Both of those values are
; copied into /flagadr/ by the following 3 mov instructions:
;
;
         mov   ax,word ptr [flag]  ;save the offset of passed
         mov   cs:flagadr,ax       ;integer variable /flag/ in
;                                  ;memory location /flagadr/
;
;
; That saves the offset that we passed, now we save the data segment
; pointer that is in ds at the time of the call. Since QuickBasic
; only has one data segment for integer variables, ds will already be
; pointing to the segment containing our /flag/ variable.
;
; We could pass the segment pointer when we made the call from
; QuickBasic by preceding the variable name with the SEG keyword; in
; that situation, QuickBasic would push the full 4-byte address onto
; the stack. We could also use the CALLS statement to call this
; routine, instead of CALL, because that statement always passes the
; full address of parameters.  But neither of those actions are
; required, because QuickBasic only has one data segment
;
; The following mov instruction saves our data segment for DOS to
; use to find our variable when it executes the interrupt routine:
;
;
         mov   cs:flagadr+2,ds     ;save the segment pointer
;                                  ;of passed integer variable
;                                  ;/flag/ in second word
;                                  ;of /flagadr/ --
;                                  ;that's what DOS needs when
;                                  ;the interrupt is called
;
;
; Next step is flagcheck to prevent multiple calls to this routine
; if it has not been reset.  Without this check, a second call would
; save our new handler address as the original.
;
; Check to see if we have already installed the vector to the
; interrupt handler routine.  If we have, we don't want to do it
; again, because we will lose the original vector
;
         mov   al,cs:[IntSetFlag]  ;get flag to see if handler
         cmp   al,0                ;is already installed
         jne   EndSet              ;if set, we have installed
;                                  ;so go to exit
;
         mov   al, 1               ;else set the flag
         mov   cs:[IntSetFlag],al
;
;
;                                  ;pick up original vector contents
;
         mov   ax,3521H            ;for interrupt 21H (MS-DOS Services
         int   21H                 ;Function Request handler)
;
         mov   cs:Old21Offset,bx   ;save the original vector
         mov   cs:Old21Segment,es  ;in our data area
;
;
;                                  ;a call to DOS services INT21H for
;                                  ;the SET INTERRUPT function 25xxH
;                                  ;requires ds:dx to be set to the
;                                  ;interrupt address, so the next two
;                                  ;statements set the ds segment
;                                  ;equal to the cs segment, where
;                                  ;our new handler procedure is
;                                  ;located
;
;
         push  cs                  ;push our code segment onto stack
         pop   ds                  ;pop it back off to set ds
;                                  ;i.e. sets ds=cs
;
         mov   dx,offset QDualDisp ;load offset of our Int 21 handler
         mov   ax,02521H           ;and reset vector to point to
         int   21H                 ;our procedure
;
;
;         pop   ds                 ;restore registers and
;         pop   es                 ;return to our QB program
;         pop   di
;         pop   si                 ;NOTE--TASM automatically adds
;         pop   bp                 ;the code to restore registers
;
EndSet:  ret
;
; actually, it's 'ret [ARGLEN]'    ;TASM automatically makes the
;                                  ;return discard the /flag/ address
;                                  ;bytes from the stack--the number
;                                  ;of bytes to discard was set by
;                                  ;the ARGLEN directive
;

;
;
;  Following is our new interrupt handler which is called by
;  MS-DOS whenever an Interrupt 21 MS-DOS Services Request
;  is detected.  The procedure first checks our enable flag
;  to determine if we want the dual output activated; the address of
;  this flag was passed by the QB program during the call to
;  the QFRedSet function.  If the flag is not set, we just skip our
;  handler and proceed to the regular interrupt 21 routine.
;
;  The handler then checks to see what type of service is being requested.
;  If it is a call to the DOS routines to output a character or a string
;  to STDOUT, the standard DOS output device, which is redirectible and
;  is always designated with file handle 1, then our procedure essentially
;  duplicates the routine by sending the output to STDERR, the standard
;  DOS error output device, which is always the display, file handle 2,
;  and whose output cannot be redirected.  Then the handler exits to the
;  normal Interrupt 21 procedure to let it process the original call.
;
;  Note that the routine is part of the QFRedSet procedure, but it is never
;  executed when that procedure is called by the QB program, because that
;  procedure ends at the 'ret' opcode at EndSet, above.
;
QDualDisp:

         pushf                     ;save everything we can --
         push  ax                  ;i.e. all registers and flags
         push  bx
         push  cx           ;note that we save the flags
         push  dx           ;even though DOS did the same
         push  bp           ;thing when it called the
         push  si           ;interrupt routine
         push  di


         push  bx                  ;save entering register values
         push  ds
         mov   bx,cs:flagadr       ;get address of flag value passed
         mov   ds,cs:flagadr+2     ;from our QB program
         mov   al,ds:bx            ;get flag value into al
         pop   ds                  ;retrieve register values
         pop   bx

         or    al, al              ;see if value was zero
         je    EndOur21            ;yes, don't do anything, go
                                   ;to the regular interrupt 21 routine

         cmp   ah,02               ;was it a call to write character to STDOUT
         jne   Int9Chk             ;no, jump to next check

         push  ds                  ;yes, save entering data segment value
         push  cs                  ;set ds=cs
         pop   ds
         mov   cs:character,dl     ;save the character to write in character
         mov   ah,40h              ;set up for int 21 function 40h
                                   ;to write character to output device
         mov   bx,2                ;set file handle=2 for STDERR
         mov   dx,OFFSET character ;get the pointer to the character
         mov   cx,1                ;one character to be written
         pushf                     ;save current flag status
         call  dword ptr cs:[Old21];use old interrupt routine to output
                                   ;the character to the display,
                                   ;it will pop the flags saved on stack
                                   ;when it returns, because it ends with
                                   ;iret, since it is an interrupt routine
         pop   ds                  ;retrieve our character
         jmp   short EndOur21      ;exit to old routine to write the character
                                   ;to redirected output

Int9Chk:
         cmp   ah,09               ;was it a call to write string to output
         jne   Int40Chk            ;no, go to next check

Chrloop:
         mov   si,dx               ;yes, set index
         cmp   byte ptr ds:[si],'$';are we at the end of the string
         je    End2109             ;yes, go to finish
         mov   ah,40h              ;no, set up for int 21 function 40h
         mov   bx,2                ;output to STDERR
         mov   cx,1
         push  dx
         pushf
         call  dword ptr cs:[Old21];write the character as above
         pop   dx
         inc   dx                  ;bump index to next character
         jmp   short Chrloop       ;loop until done
End2109:
         jmp   short EndOur21      ;exit to old routine to write the character
                                   ;to redirected output

Int40Chk:
         cmp   ah,40h              ;was it a call to write to file or device
         jne   EndOur21            ;no, done, exit to regular int 21

         cmp   bx,1                ;yes, then was it a call to STDOUT
         jne   EndOur21            ;no, done, exit

         push  ds                  ;yes, save character
         mov   bx,2                ;set file handle for STDERR
         pushf
         call dword ptr cs:[Old21] ;use old interrupt routine to output
         pop   ds                  ;retrieve character

EndOur21:

                                   ;retrieve registers
         pop   di                  ;this resets registers
         pop   si                  ;and flags to exactly
         pop   bp                  ;where they were when we
         pop   dx                  ;entered our custom handler
         pop   cx
         pop   bx
         pop   ax
         popf
;
;
         jmp dword ptr cs:[Old21]  ;go to regular int 21 routine
;
;
;
;
QFRedSet  endp
;
;
;
;  The subroutine QFRedOff is called by the QB program to
;  return the MS-DOS interrupt vector 21H to its' original state.
;  The subroutine is used in the form:
;
;                   CALL QFRedOff()
;
;
QFRedOff  proc  uses si di es ds   ;Restore MS-DOS Services
;                                  ;interrupt vector 21H
;         push  bp                 ;to its' original state
;         mov   bp,sp
;         push  ds                 ;same code added as above
;         etc.
;
;
;  First we must check our IntSetFlag to see if the
;  vectors to our handler were installed; if not, we
;  do not want to reset them here, either
;
;
         mov   al,cs:[IntSetFlag]  ;Get our inhibit flag
         cmp   al,1                ;see if it is set
         jne   EndOff              ;no, go to exit
                                   ;else, reset vector
;
;
         mov   dx,cs:Old21Offset   ;Set interrupt 21H MS-DOS
         mov   ds,cs:Old21Segment  ;Services Request
         mov   ax,02521H           ;back to its' original vector
         int   21H
;
;
         mov   al, 0               ;reset the flag to enable
         mov   cs:[IntSetFlag],al  ;the QFRedSet routine
;
;         pop   ds                 ;restore registers and
;         pop   bp                 ;return to QB program --
;         etc.                     ;same exit code added as above
;
EndOff:  ret
;
QFRedOff endp
;
;
;
IntSetFlag db  0                   ;this flag inhibits QFRedSet operation
;                                  ;after it has redirected vector
;                                  ;until QFRedOff resets it, and does
;                                  ;the same for QFRedOff if QFRedSet
;                                  ;has not redirected vector
;
flagadr  dw    0,0                 ;Long address of QB program's
;                                  ;display redirected output flag --
;                                  ;note that each '0' is actually 2 bytes
;
Old21          Label Dword
Old21Offset    dw ?                ;Original contents of MS-DOS
Old21Segment   dw ?                ;Interrupt 21H vector

;
;
character      DB ?                ;storage for output character
;

         end