(* ---
 
   Patch to the time of day function in Design/CPN

   Created 13/01/2003

   Description:

   The Design/CPN state space tool relies on the tod () function
   in the SML base to implement the stop criteria for time. 

   The tod() function returns a 31 bit signed integer representing the 
   number of seconds since January 1, 1970. This will result in an overflow 
   after 1073741823 seconds which is in the beginning of January 2004. The user
   of the Design/CPN state space tool will see this as the state space generation 
   stopping immediately after the generation has been started.

   This piece of SML code provides a patch for this problem by
   redefining the tod () function but preserving its type. The patch
   is not _the_ proper way of solving the problem, but it is the
   solution that requires the fewest changes to the SML code. In
   particular users should note that

   1) The patch will not work if you set back the clock of your
      machine past January 1, 1970 + 1073741823 seconds.

   2) It will only fix the tod() function until the early morning of
      Jannuary 19, 2034 (by then we hope that you have all swicthed to
      CPN Tools++ 64 bit architectures).

   3) You can no longer use the tod () function to compute the
      absolute time using January 1, 1970 as a base. The base is now
      January 1, 1970 + 1073741823 seconds.

   The proper way of fixing the problem would be to have the tod()
   return a 32bit integer, but that would require changes to a number
   of files in the state space tool since then the return type of the
   function changes.

   The patch can be applied in two ways:

   1) Store this file (tod.sml) somewhere on your file system, and
   insert the following line in the beginning of your global
   declaration box:

   use ("<path>/tod.sml");

   where <path> is the directory on your file system where you saved
   the tod.sml file. 

   2) If you have the access rights required to modify your local
      Design/CPN installation you can store the file tod.sml in the
      OGMLfiles directory and modify the OGswitch.sml file by
      inserting the line:

      use (ogpath^"tod.sml");

      after the line:

      DSUI_SetStatusBarMessage("Entering Occ Graph...");

   --- *)

val gettimeofday : unit -> (Int32.int * int) = 
    Unsafe.CInterface.c_function "SMLNJ-Time" "timeofday"    

fun tod() = 
  let
      (* max int in SML on 32 bit machines (see Int.maxInt) *);
      val maxint31 =  Int32.fromInt 1073741823 

      val (secs, _) = gettimeofday()

      (* convert back into "small integers" to preserve type *)
      val secs31bit = Int.fromLarge(Int32.-(secs,maxint31))
  in
    secs31bit
  end