jeffe@eniac.seas.upenn.edu (George Jefferson ) (03/09/91)
help.. I am trying to add a bit of my own postscript code to existing code which wraps each page in a save/restore pair My problem is that I would like to pass a value (integer, string whatever) from one page to the next.. %this obviously won't do it. save . . /myx 1 def . restore . . save . . myx 10 10 string cvrs show %for example restore Is there a way to store a value at some low level which is not destroyed by restore? I do not want to try to defeat the restore all together, just pass 1 value. -- -george george@mech.seas.upenn.edu
fj@iesd.auc.dk (Frank Jensen) (03/11/91)
In article <38972@netnews.upenn.edu> jeffe@eniac.seas.upenn.edu (George Jefferson ) writes:
help..
I am trying to add a bit of my own postscript code
to existing code which wraps each page in a save/restore pair
My problem is that I would like to pass a value (integer, string whatever)
from one page to the next..
%this obviously won't do it.
save
.
.
/myx 1 def
.
restore
.
.
save
.
.
myx 10 10 string cvrs show %for example
restore
Is there a way to store a value at some low level which is not
destroyed by restore?
I do not want to try to defeat the restore all together, just pass 1 value.
Try: myx % load the value of `myx' onto the operand stack
restore
exch /myx store % pop the value on top of the operand stack
% and store it
save
Just make sure that the value of `myx' is not a composite object where
some of the components were allocated inside the save/restore pair.
In that case you will get an `invalid restore' error.
--
-george george@mech.seas.upenn.edu
--
Frank Jensen, fj@iesd.auc.dk
Department of Mathematics and Computer Science
Aalborg University
DENMARKwoody@chinacat.Unicom.COM (Woody Baker @ Eagle Signal) (03/11/91)
In article <38972@netnews.upenn.edu>, jeffe@eniac.seas.upenn.edu (George Jefferson ) writes: > help.. > > I am trying to add a bit of my own postscript code > > > Is there a way to store a value at some low level which is not > destroyed by restore? I seem to remember that on at least on older version of PS, there was a bug that allowed you to do this. I think it was something like if you created a string, then put a character into it with put, it would survive a save/restore pair. I know that Don Lancaster published some thing about it, and even wrote code to use it, but IT IS A BUG AND IS NOT REPEATABLE unless you have the buggy interpreter. i.e. Not wise to write code for others use that depends on it. Cheers Woody
cet1@cl.cam.ac.uk (C.E. Thompson) (03/11/91)
In article <1909@chinacat.Unicom.COM> woody@chinacat.Unicom.COM (Woody Baker @ Eagle Signal) writes: > >I seem to remember that on at least on older version of PS, there was a bug >that allowed you to do this. I think it was something like if you created >a string, then put a character into it with put, it would survive a >save/restore pair. I know that Don Lancaster published some thing about it, >and even wrote code to use it, but IT IS A BUG AND IS NOT REPEATABLE >unless you have the buggy interpreter. > >i.e. Not wise to write code for others use that depends on it. > Well, there are much cleaner ways of passing data out through a save/restore boundary than to use this feature/bug. However, it is morally certain that all PostScript interpreters that have ever existed have had the feature/bug. In fact, in the 2nd edition of the LRM (orange-and-white book) Adobe seem to have given up claiming that this will ever change. Page 60, section 3.7.3, "restore resets the values of all composite objects in local VM, except strings, to their state at the time of the save"; and there is no equivalent to the footnote on p.44 of the old LRM (red book). Chris Thompson JANET: cet1@uk.ac.cam.phx Internet: cet1%phx.cam.ac.uk@nsfnet-relay.ac.uk
leland@cs.columbia.edu (Lee Woodbury) (03/12/91)
In article <1909@chinacat.Unicom.COM> woody@chinacat.Unicom.COM (Woody Baker @ Eagle Signal) writes: >In article <38972@netnews.upenn.edu>, jeffe@eniac.seas.upenn.edu (George Jefferson ) writes: >> Is there a way to store a value at some low level which is not >> destroyed by restore? >I seem to remember that on at least on older version of PS, there was a bug >that allowed you to do this. I think it was something like if you created >a string, then put a character into it with put, it would survive a >save/restore pair. I know that Don Lancaster published some thing about it, >and even wrote code to use it, but IT IS A BUG AND IS NOT REPEATABLE >unless you have the buggy interpreter. > >i.e. Not wise to write code for others use that depends on it. Yeah, this is referred to in a footnote on p.43 in Section 3.7, "VIRTUAL MEMORY," of the Red Book (1st ed): In the current PostScript design, restore actually does not undo changes made to the elements of strings. We consider this behavior to be a defect, and we do not recommend that PostScript programs take advantage of it. Leland Woodbury -- INTERNET: leland@cs.columbia.edu USENET: ...!columbia!cs.columbia.edu!leland BITNET: leland%cs.columbia.edu@cuvmb USMAIL: Columbia Univ., 457 CS, 500 W. 120 St., NYC 10027-6699
jtkohl@MIT.EDU (John T Kohl) (03/14/91)
In article <38972@netnews.upenn.edu> jeffe@eniac.seas.upenn.edu (George Jefferson ) writes: > I am trying to add a bit of my own postscript code > to existing code which wraps each page in a save/restore pair > My problem is that I would like to pass a value (integer, string whatever) > from one page to the next.. I thought someone would have mentioned it by now, but... The trick I've used on occasion is to leave a value on the stack. The hard part is usually making sure it's in the right place on the stack and doesn't get wiped by other operators. This might be helped by using a mark and counttomark to figure out how far to roll the stack to deposit the value. Again, make sure it's not a composite object. An integer should be no problem.... -- John Kohl <jtkohl@ATHENA.MIT.EDU> or <jtkohl@MIT.EDU> Digital Equipment Corporation/Project Athena (The above opinions are MINE. Don't put my words in somebody else's mouth!)
jeffe@eniac.seas.upenn.edu (George Jefferson ) (03/14/91)
I basically got two responses. Many people sugested leaving my value on the stack. I suppose my question was not as well posed as it could have been, but there is a _lot_ of code between the 'restore' and the place where I am allowed to insert my code. I would have to be very careful with the stack indeed :-) Several people mentioned the feature/bug of strings being exempt from restore - ing. I am trying to write something which will be very portable, but I think I would try this as a last resort. my own answer was.. think of a way to avoid the problem.. thanks to all these people (and probably a few that I missed) John Kohl Leland Woodbury Robert A. Lerche Dick Dunn Berthold K.P. Horn Jacques Kors Mark Zellers Frank Jensen Luigi Perrotta Chris Thompson woody -- -george george@mech.seas.upenn.edu
fj@iesd.auc.dk (Frank Jensen) (03/15/91)
In article <39120@netnews.upenn.edu> jeffe@eniac.seas.upenn.edu (George Jefferson ) writes: ... Many people sugested leaving my value on the stack. I suppose my question was not as well posed as it could have been, but there is a _lot_ of code between the 'restore' and the place where I am allowed to insert my code. I would have to be very careful with the stack indeed :-) I don't see the problem. Suppose you have a special dictionary you use to store your values, call it `mydict'. Then you can use this dictionary at will, provided you redefine `restore': /-restore /restore load def % save old `restore' operator /restore { mydict {} forall mydict length % load values onto the stack dup 2 mul 2 add -1 roll % get restore object -restore % do the restore mydict begin {def} repeat end % save the values } def -- -george george@mech.seas.upenn.edu -- Frank Jensen, fj@iesd.auc.dk Department of Mathematics and Computer Science Aalborg University DENMARK