clear local fn recode( t as CFStringRef, code as CFStringRef ) as CFStringRef
  CFStringRef s = @""
  Short i, k, w = sqr( len( code ) )

  for i = 0 to len( t ) - 1 step 2
    k = intval( mid( t, i, 2 ) ) // Get ‘coordinates’ of char in code string
    k = w * ( k / 10 ) + k mod 10
    s = fn StringByAppendingString( s, mid( code, k, 1 ) )
  next

end fn = s

//

clear local fn encode( s as CFStringRef, code as CFStringRef ) as CFStringRef
  CFStringRef a = @"", b = @"", c
  Short i, k, w = sqr( len( code ) )
  if w == 5 then s = fn StringByReplacingOccurrencesOfString( s, @"J", @"I" )
  print s

  for i = 0 to len( s ) - 1
    c = mid( s, i, 1 )
    k = instr( 0, code, c ) // Put row in one string, column in the other
    a = fn StringByAppendingString( a, fn StringWithFormat( @"%d", k / w ) )
    b = fn StringByAppendingString( b, fn StringWithFormat( @"%d", k mod w ) )
  next

  a = fn StringByAppendingString( a, b ) // Combine the two strings, and recode

end fn = fn recode( a, code )

//

clear local fn decode( s as CFStringRef, code as CFStringRef ) as CFStringRef
  CFStringRef a = @"", b = @"", c
  Short i, k, w = sqr( len( code ) )

  for i = 0 to ( len( s ) - 1 )
    c = mid( s, i, 1 )
    k = instr( 0, code, c ) // Put row and columm in one long string
    a = fn StringByAppendingString( a, fn StringWithFormat( @"%d%d", k / w, k mod w ) )
  next

  for i = 0 to len( a ) / 2 - 1 // Take row from first half of string, column from second
    c = fn StringByAppendingString( mid( a, i, 1 ), mid( a, i + len( a ) / 2 , 1 ) )
    b = fn StringByAppendingString( b , c ) // Combine, and recode
  next

end fn = fn recode( b, code )

//

print fn encode( @"ATTACKATDAWN", @"ABCDEFGHIKLMNOPQRSTUVWXYZ" )
print fn decode( @"DQBDAXDQPDQH", @"ABCDEFGHIKLMNOPQRSTUVWXYZ" )
print
print fn encode( @"FLEEATONCE", @"BGWKZQPDNSIOAXEFCLUMTHYVR" )
print fn decode( @"UAEOLWRINS", @"BGWKZQPDNSIOAXEFCLUMTHYVR" )
print
print fn encode( @"HAPPY40THDAD", @"ABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789" )
print fn decode( @"GO31GAGVANJD", @"ABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789" )

handleevents