NetNews Usenet Archive 1993 #3/NN_1993_3.iso/spool/comp/sys/mac/programm/22029

Text File | 1993-01-24 | 1.9 KB | 58 lines

Newsgroups: comp.sys.mac.programmer
Path: sparky!uunet!munnari.oz.au!uniwa!cujo!ncrpda.curtin.edu.au!rocky.curtin.edu.au!user
From: [e-mail] (Peter N Lewis)
Subject: Re: Verifying valid handles, how to?
Message-ID: <[e-mail]>
Followup-To: comp.sys.mac.programmer
Lines: 44
Sender: [e-mail]
Nntp-Posting-Host: ncrpda.curtin.edu.au
Organization: NCRPDA, Curtin University
References: <[e-mail]>
Date: Sat, 23 Jan 1993 10:01:36 GMT

In article <[e-mail]>, [e-mail]
wrote:

> the handle is stored in register a1.  I don't know, however, how to check
> if it is a valid handle without causing an error (bus or otherwise) of
> somesort.  Especially if it is a random number!  Anyone know?  Is there

here's a random attempt at it.  First check that the handle is even.  Then
check that it points to an area inside your heap or inside the system heap,
then check that h^ is inside the heap as well, and finally that recover
handle gives the right value.

 function InsideHeap (p: univ ptr; hz: THz): boolean;
 begin
  InsideHeap := (longInt(p) >= longInt(hz)) & (longInt(p) <
longInt(hz^.bkLim));
 end;

 function ValidHandle (h: univ handle): boolean;
  var
   valid: boolean;
 begin
  valid := false;
  if BAND(h, 1) = 0 then begin
   if InsideHeap(h, ApplicZone) then begin
    valid := (BAND(h^, 1) = 0) & InsideHeap(h^, ApplicZone);
   end
   else if InsideHeap(h, SystemZone) then begin
    valid := (BAND(h^, 1) = 0) & InsideHeap(h^, SystemZone);
   end;
  end;
  if valid then begin
   valid := RecoverHandle(h^) = h;
  end;
  ValidHandle := valid;
 end;

(Code tried and tested, but by no means guarenteed)

That would seem to be a good start...
   Peter.

_______________________________________________________________________
Peter N Lewis <[e-mail]>             Ph: [phone]