rem  Set the logged drive ('A' to 'P')
procedure setdrive (drive = char)
   var hl, de, bc, a_psw = integer
   rem -- make sure drive letter is upper case!
   if drive >= 'a' then drive = drive - 32
   hl = 0
   de = drive - 65
   bc = 0EH
   a_psw = 0
   call (5H,hl,de,bc,a_psw)
end

rem  Set the CP/M user area (0 to 15)
procedure setuser (user = integer)
   var hl, bc, a_psw = integer
   hl = 0
   bc = 20H
   a_psw = 0
   call (5H,hl,user,bc,a_psw)
end

comment
   Return size of named file as number of 128-byte records;
   assumes file name is upper case. If the file does not
   exist, the size will be reported as 0.
end
function fsize(filename = string:20) = integer
    var hl, de, bc, a_psw, p = integer
    based fname = string:20
    based sz = integer
    dim byte workfcb(36)
    location array de = workfcb
    base fname at de
    base sz at de + 33
    fname = fcb$(filename)
    rem  See if drive was specified and set FCB accordingly
    p = instr(1,filename,":")
    if p = 0 then
    	workfcb(0) = 0
    else
      workfcb(0) = asc(mid(filename,p-1,1)) - 64
    bc = 23H			  rem  BDOS filesize function
    call (5,hl,de,bc,a_psw)     rem  result stored in sz
end = sz

rem  Exercise the function

var filename = string:20
filename = "INPUT.TXT"
rem  First check current drive and user
print filename;" occupies";fsize(filename)*128;" bytes"
rem  Then check startup directory (A0:)
setdrive 'A'
setuser 0
print "A0:INPUT.TXT occupies";fsize(filename)*128;" bytes"

end