$CPU 8086          ' make compatible with XT systems
$LIB ALL OFF       ' turn off all PowerBASIC libraries
$ERROR ALL OFF     ' turn off all PowerBASIC error checking
$OPTIMIZE SIZE     ' optimize for smaller code
 $COMPILE UNIT      ' compile to a UNIT (.PBU)
'$COMPILE EXE       ' compile to a UNIT (.PBU)

DEFINT A-Z         ' Required for all numeric functions, forces PB to not
                   ' include floating point in UNIT (makes it smaller)
'/*------------------------------------------------------------------*/
$CODE SEG "MLIB1"
'/*------------------------------------------------------------------*/
' GetDTA - Get Disk Transfer Address (DTA) from DOS
'
' DtaSeg = Returned segment of the DTA
' DtaOfs = Returned offset of the DTA
'
' The DTA is usually located in the PSP.  However, any routine that
' calls the FINDFIRST, FINDNEXT functions from DOS (such as the
' PowerBASIC statement DIR$) can change the location of the DTA.
' This sub-routine uses DOS interrupt 21h, function 2Fh, to get
' the current location of the DTA.
'
SUB GetDTA(DtaSeg AS INTEGER, DtaOfs AS INTEGER) PUBLIC

  ! push DS                      ; save DS for PowerBASIC

  ! mov  AX, &H2F00              ; function 2Fh, get DTA location
  ! int  &H21                    ; call DOS

  ! lds  SI, DtaSeg              ; point DS:SI at DtaSeg
  ! mov  DS:[SI], ES             ; put segment of DTA in variable

  ! lds  SI, DtaOfs              ; point DS:SI at DtaOfs
  ! mov  DS:[SI], BX             ; put offset of DTA in variable

  ! pop  DS                      ; restore DS for PowerBASIC

END SUB
'/*------------------------------------------------------------------*/
' Exist - Return true (-1) if a given filespec exists.  Preserves the DTA.
'         Calling any of the DTA routines after Exist will return invalid
'         results because of the DTA preservation.
'
' Filename = name of file or directory to test for the existence of
'
'/*------------------------------------------------------------------*/
' EXIST(FILESPEC$)
'     Retuns a 1 if the file exists and a zero if the file is not
'     found.
'     EXMAPLE:  EXIST("C:\TESTER.DAT")
'/*------------------------------------------------------------------*/
FUNCTION EXIST(BYVAL Filename AS STRING) PUBLIC AS INTEGER

  DIM DtaSeg       AS INTEGER
  DIM DtaOFs       AS INTEGER
  DIM OldDtaBuffer AS STRING

  GetDTA DtaSeg, DtaOfs

  DEF SEG = DtaSeg
    OldDtaBuffer = PEEK$(DtaOfs, 44)     'save current DTA information
  DEF SEG

  T = LEN( DIR$(Filename, 17) ) > 0
  IF T = -1 THEN FUNCTION = 1 ELSE FUNCTION = 0
  DEF SEG = DtaSeg
    POKE$ DtaOfs, OldDtaBuffer           'restore saved DTA information
  DEF SEG

END FUNCTION
'/*------------------------------------------------------------------*/
'   CLS
'   PRINT "TESTING EXIST FUNCTION"
'   PRINT EXIST("C:\AUTOEXEC.BAT")
'   PRINT EXIST("C:\TEST.BAT")
'   PRINT EXIST("C:\CONFIG.SYS")
'   IF EXIST("C:\AUTOEXEC.BAT") THEN PRINT "YES" ELSE PRINT "NO"
'   IF EXIST("C:\DODDLE.BAT") THEN PRINT "YES" ELSE PRINT "NO"
'   INPUT Z
'/*------------------------------------------------------------------*/