Challenge: Validate a code

[Moneo]

ANTONI,
Your "bit array" is exactly my preferred solution. See my program below with a slightly simpler bit handling than yours, that is, no need for a pwrsof2 array.

Code:

REM Code validation program by Edward F. Moneo
DEFINT A-Z
CONST BT.MAXSIZE = 99999
DIM BT.TAB ( 0 TO ((BT.MAXSIZE+1)\16) ) AS INTEGER
DIM BT.BIT  AS LONG
DIM BT.LOC  AS INTEGER
DIM BT.ARG  AS LONG
DIM BT.TRUE AS INTEGER

open "valid.txt" for input as #1
do while not eof(1)
   line input #1,d$
   bt.arg=val(d$)
   gosub bt.set
loop

do
  input "Enter code to be validated (X=exit)";z$
  if ucase$(z$)="X" then system
  gosub validate
  if valid=0 then
     print "ERROR: Non-numeric or out or range input code"
  else
     bt.arg=val(z$)
     gosub bt.test
     if bt.true=0 then print "ERROR: code invalid" else print "ok, code valid"
  end if
loop

'******************************************************************************

BT.SET:
  GOSUB BT.GET
  BT.TAB(BT.LOC) = BT.TAB(BT.LOC) OR BT.BIT
RETURN

BT.TEST:
  GOSUB BT.GET
  BT.TRUE = ( BT.TAB(BT.LOC) AND BT.BIT )    
RETURN

BT.GET:
  BT.BIT = BT.ARG MOD 16
  BT.BIT = 2^BT.BIT
  BT.LOC = BT.ARG\16
RETURN

'BT.RESET:  '(Not used by this program)
'  GOSUB BT.GET
'  BT.TAB(BT.LOC) = BT.TAB(BT.LOC) AND (NOT(BT.BIT))
'RETURN
'  *************************************************************************

'*** CHECK FOR STRICTLY NUMERIC AND LESS/EQUAL TO BT.MAXSIZE.
VALIDATE:
  VALID=0         'Init to False
  IF Z$="" THEN RETURN '------------------
  FOR X = 1 TO LEN(Z$)
      A=ASC(MID$(Z$,X,1))
      IF A<48 OR A>57 THEN RETURN '-------
  NEXT X
  IF VAL(Z$)<=BT.MAXSIZE THEN VALID=-1
RETURN

*****