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+TeX 3.14159 and other updates -- file 1 of 2
+
+This and the following messages contain the details of bug reports
+sent to Don Knuth, edited somewhat for brevity, and his responses.
+
+As already announced, the new release -- TeX 3.14159, MF 2.718 and
+related TeX- and MFware -- is at labrea.stanford.edu in the file
+~ftp/alpha/tex95.tar.gz . No arrangements have been made yet to
+install the unpacked versions into the /tex area at labrea, from
+which it can be mirrored to CTAN; I will try to do that as soon
+as possible.
+
+This message begins with a complete contents list of the main topics
+in this collection, to help you find items of interest quickly. I
+have just sent out the reward checks with the annotated originals
+of the reports as Don returned them to me. They should be arriving
+at their destinations soon.
+
+
+########################################################################
+
+Contents:
+ >>> TeXbook / MFbook / documentation bugs
+ +++ glitch in errata.five at labrea
+ +++ MFbook, page 134 and others from Robert Hunt
+ +++ MFbook, page 143
+ +++ MFbook, several from Denis Roegel
+ +++ Spurious TAB in errorlog.tex
+ >>> The TeX program
+ +++ trap_zero_glue bugette
+ +++ font_mem_max and other memory parameters
+ [ continued in file message.045 ]
+ >>> plain.tex
+ +++ \oalign and \d{}
+ +++ hyphenation inhibited by struts
+ +++ TeXbook, page 363, in \endinsert
+ >>> Metafont
+ +++ arithmetic overflow with z=whatever[z',z'']
+ +++ several reports from Bogus{\l}aw Jackowski
+ >>> CM fonts
+ +++ missing "cmchar"s in bigdel.mf
+ +++ shaved_stem vs. cap_stem in greeku.mf
+ +++ miscellanea from Robert Hunt, mostly in CM sources
+ +++ cap_ess in cmmi12 and larger
+ +++ possible glitch in cmbx5 and cmbx6
+ +++ arithmetic overflow in CMinch
+ +++ sterling sign
+ >>> Fontware
+ +++ testfont.tex
+ +++ VPtoVF
+
+************************************************************************
+[ dek --
+ Robert Hunt: C134 $2.56, C207 $2.56, C257 $2.56, A354 $2.56,
+ A359 $2.56, A360 $2.56, A361 $2.56, A362 $2.56,
+ A362 $2.56, E95(97) $2.56, E187 $2.56, E113 $2.56,
+ E233 $2.56, E438 $2.56, C129 $2.56, E491 $2.56
+ Chris Thompson: C206 $2.56, TeX\S549 $327.68
+ Michael Barr: A357 $2.56
+ Peter Schmitt: C143 $.32
+ Marek Ry\'cko: A31 $2.56
+ Bogus\l{}aw Jackowski: MF\S815 $327.68, CSCSPU bugfix $2.56
+ Denis B. Roegel: C94 $2.56, C107 $2.56, C355 $2.56
+ Eberhard Mattes: TeX\S634 $2.56
+ Jim Sterken: TeX\S625 $2.56
+ Rainer Schoepf: B503 $2.56
+ Bernd Raichle: A374 $.32
+ Barbara Beeton: C354 $2.56
+ Berthold Horn: TeX\S1323 $20.48
+ Pierre MacKay: E291 $.32
+ Walter Carlip: TeX\S717 $10.24
+ Andrew K. Trevorrow: TeX\S549 $20.48
+ Yannis Haralambous: E239 $2.56
+ J"org Knappen: A356 $2.56
+ Petr Sojka: A356 $2.56
+ Ulrik Vieth: A363 $2.56
+]
+
+>>> TeXbook / MFbook / documentation bugs
+
+ +++ glitch in errata.five at labrea
+
+in errata.five:
+ \bugonpage C282, the three lines following the chart (9/39/89)
+should be ^
+ \bugonpage C282, the three lines following the chart (9/30/89)
+[ dek * ]
+
+ ----------------------------------------------------------------------
+
+ +++ MFbook, page 134 and others from Robert Hunt
+
+Date: Thu, 16 Apr 92 15:57:44 BST
+From: Chris Thompson <CET1@phx.cam.ac.uk>
+To: Barbara Beeton <BNB@MATH.AMS.COM>
+Cc: Robert Hunt <REH10@phx.cam.ac.uk>
+Subject: MFbook p.134 bug from Robert Hunt
+
+Here is another one from Robert:
+
+> MFbook, page 134 (line 7933 of mfbook.tex) should read
+> ...if $t\le 0$, precontrol~$t$ of~$p$ is~$z_0$.
+> (rather than $z_n$).
+[ dek -- $2.56
+]
+
+He's right. The z_n has somehow got duplicated from the previous
+sentence.
+
+Chris Thompson
+JANET: cet1@uk.ac.cam.phx
+Internet: cet1@phx.cam.ac.uk
+-------
+Date: Thu, 07 May 92 22:37:53 BST
+From: Chris Thompson <CET1@phx.cam.ac.uk>
+To: Barbara Beeton <BNB@MATH.AMS.COM>
+Cc: Robert Hunt <REH10@phx.cam.ac.uk>
+Subject: Miscellany from Robert Hunt
+
+Barbara,
+
+ Here are three things from Robert Hunt (his messages to me marked
+with ">"):
+
+1. (7 May):
+[ this has been resolved already ]
+
+2. (22 Apr, after I had been publicising the errata.* files locally):
+> Is there any way of telling how far back it's necessary to go through
+> the "Bugs in Computers and Typesetting" files in order to make sure
+> that you have all the necessary changes? I very recently bought a copy
+> of the softback version of the METAFONTbook, which says "6th printing,
+> revised, February 1991" inside; but some of the changes listed in even
+> only the third file (which covers the period up to June 1987) have not
+> been made to it. As a typical example, the correction to page 14 (to
+> mention Paul de Casteljau as the discoverer of the recursive midpoint
+> rule) has not been made; but the correction to page 348, to include
+> his name in the index, has! The same is true of the bugs listed in the
+> fourth file and so on, which makes the book somewhat inconsistent in
+> places. Is it possible that the printers have accidentally lost some
+> of the updates, perhaps?
+[ dek -- yes
+ AW totally screwed this up and i was bl**dy *ngry
+]
+
+I must admit I didn't entirely believe this until Robert actually
+turned up with his copy of the book today: the example he gives is
+certainly correct. Very odd. Do you know whether anything more than
+usually peculiar happened to the 6th softcover printing? (The current
+mfbook.tex at labrea purports to represent the 7th softcover printing.)
+If not, who could answer Robert's questions?
+
+3. (7 May):
+> My candidate for the most trivial error in the METAFONTbook: on page
+> 207, line 10, "-.00005" should read "-0.0005".
+
+Yes, that is an error, not yet fixed in mfbook.tex. But I'm sure we can
+find one yet more trivial, can't we? ...
+
+Actually, I tried to reproduce the numbers on pages 206-207 by
+[ dek -- $2.56
+]
+compiling io.mf (from labrea) with mode=lowres;autorounding:={0 or 1};
+tracingspecs:=1 and I get numbers a teeny bit different from what is
+in the text. For example, instead of "point (10.85146,-0.0005), where
+there was a horizontal tangent, has been rounded to (10.85872,0)", I get
+(10.85147,-0.00049) and (10.85873,0). Maybe the rounding details in MF
+have changed since DEK did the run that produced these numbers.
+[ dek -- $2.56
+ Yes that was either bug #550 or 560. or both
+]
+
+Chris Thompson
+JANET: cet1@uk.ac.cam.phx
+Internet: cet1@phx.cam.ac.uk
+-------
+Date: 19 May 1992 22:50:35 -0300 (BST)
+From: Chris Thompson <CET1@phx.cam.ac.uk>
+Subject: Yet another MFbook bug from Robert Hunt
+
+Barbara,
+
+ The following from Robert Hunt (11 May; I was ill last week and
+am only now getting round to clearing some of the backlog):
+[ dek -- (and here i sit on a chilly day in California 26 Feb 199_5_,
+ coughing as I try to reduce the _secondary_ backlog.)
+ Hope you're feeling better by now, Chris!
+]
+
+> On page 257 of the METAFONTbook, line 5 (the large centred display),
+> the bracketed entries |numeric| |<| |numeric| (etc.) should read
+> \<numeric> |<| \<numeric> instead.
+[ dek -- $2.56
+ (maybe should be $2.57 instead?)
+]
+
+He's right: the two stacks (boolean, numeric, pair, string, transform)
+should be <...> types, not boldface words, for consistency with the
+rest of Appendix B. Not fixed in the latest mfbook.tex available to me.
+
+Chris Thompson
+-------
+[ dek -- However -- Why was I not told this in 1992 or 1993?
+ I could then have fixed the final printing of MFbook.
+ Changes since 93 affect the electronic copy _only_;
+ the hardcopy is frozen now for vols A, B, C, E.
+]
+
+ ----------------------------------------------------------------------
+
+ +++ MFbook, page 143
+
+Date: Thu, 08 Jul 93 15:03:58 MEZ
+From: Peter Schmitt <A8131DAL@AWIUNI11.EDVZ.UniVie.AC.AT>
+To: INFO-TEX <@cunyvm.cuny.edu:INFO-TEX@SHSU.BITNET>
+Subject: bugs in MFbook and TeXbook
+
+Since this topic is just discussed:
+ I recently noticed two `bugs' in the MFbook which
+ --- as far as I could see from the Errata --- have not
+ yet been corrected:
+
+%%%%
+The METAFONTbook
+Fourth printing, revised, September 1991
+
+[ first one has been fixed ]
+
+page 143, line 2 : `giving the next exprs:'
+ should read `giving the next expressions:'
+%%%%
+
+[...]
+
+Peter
+
+Peter Schmitt a8131dal@awiuni11.edvz.univie.ac.at
+ schmitt@awirap.bitnet
+-----------------------------------------------------------------------------
+Institute of Mathematics Strudlhofgasse 4
+[ dek -- great name ^^^^^^^^^^^^^^
+]
+University of Vienna A-1090 Wien
+ Austria
+-------
+Date: 08 Jul 1993 15:37:56 -0300 (BST)
+From: Chris Thompson <CET1@phx.cam.ac.uk>
+To: Peter Schmitt <A8131DAL@AWIUNI11.EDVZ.UNIVIE.AC.AT>
+Subject: Re: [bugs in MFbook and TeXbook]
+
+Reply to Peter Schmitt, copied to Barbara Beeton.
+
+[...]
+
+> page 143, line 2 : `giving the next exprs:'
+> should read `giving the next expressions:'
+> %%%%
+
+This is unchanged in the most recent mfbook.tex available to me.
+It does read rather oddly. I wonder whether the 'expr' was meant
+to be in \tt?
+[ dek -- 32\cents
+]
+
+Chris Thompson
+-------
+[ dek -- Not an error -- when you input _expr.mf_ the computer types
+ _``Gimme an expr: ''_ and I was just appropriating that
+ neologism into English. Like `ftp' and `grep'.
+ However I do admint that a reasonable person might wonder at
+ my idiosyncratic style, so I'll change to \tt and pay the
+ normal reward of 32\cents for suggestions.
+]
+
+ ----------------------------------------------------------------------
+
+ +++ MFbook, several from Denis Roegel
+
+Date: 04 May 1994 16:58:42 +0200
+From: "Denis B. Roegel" <Denis.Roegel@loria.fr>
+Cc: roegel@lorraine.loria.fr (Denis B. Roegel)
+Subject: bugs in the METAFONTbook
+
+Mrs Beeton,
+
+I found two small bugs in my copy of the
+METAFONTbook (hardcopy). I went through the last
+erratas and found no mention of them.
+
+Here they are:
+
+1) page 94: last paragraph, 4th line: the word "are"
+ is duplicated.
+[ dek -- $2.56
+]
+
+2) [resolved ]
+
+Thak you,
+
+Denis. (roegel@loria.fr)
+-------
+Date: 05 May 1994 17:14:40 +0200 (MET DST)
+From: "Denis B. Roegel" <Denis.Roegel@loria.fr>
+Subject: Re: bugs in the METAFONTbook
+
+[...]
+
+Maybe there is another bug in the MFbook:
+
+In the first paragraph of page 115, the instruction
+"endchar" in the program at the end of chapter 12
+is mentionned. However, there is no "endchar" in
+the program at the end of chapter 12.
+[ dek -- $2.56 page 107
+]
+
+Denis.
+-------
+(reply, 05 May 1994)
+thanks for your additional report.
+the "dangerous bend" program in the file manfnt.mf is just a bit
+different from what is in the mfbook, and does end with an
+"endchar" -- preceded by another line not in the mfbook. for
+some reason, this bug (i'm sure it is!) sounds familiar to me,
+but i can't find a reference, and it's not corrected in any of
+the errata files.
+onto the dek list it goes ...
+cheers. -- bb
+-------
+
+ ----------------------------------------------------------------------
+
+ +++ Spurious TAB in errorlog.tex
+
+[ from comp.text.tex, 21 Jan 95 ]
+Date: 20 Jan 1995 12:38:36 GMT
+From: schwab@issan.informatik.uni-dortmund.de (Andreas Schwab)
+Subject: Spurious TAB in errorlog.tex
+
+There is a spurious TAB in the file systems/knuth/errata/errorlog.tex,
+as found on the CTAN, in line 2867, containing the text "(Mattes and
+Raichle). @1036". This TAB (after the word Mattes) causes a Greek Psi
+[ dek * ]
+to be typeset where a space should have been, looking a bit funny :-).
+
+--
+Andreas Schwab "And now for something
+schwab@issan.informatik.uni-dortmund.de completely different"
+===========================================================================
+[ dek -- _Thanks_
+]
+
+<<< end TeXbook / MFbook / documentation bugs
+
+************************************************************************
+
+>>> The TeX program
+
+ +++ trap_zero_glue bugette
+
+Date: 28 Oct 1993 16:26:02 +0000 (GMT)
+From: Chris Thompson <CET1@phx.cam.ac.uk>
+To: Rainer Schoepf <Schoepf@sc.ZIB-Berlin.DE>
+Subject: Re: [interesting effect in overfull box printout]
+
+Rainer,
+
+Yes, I think you have discovered a bugette. CC'ing this to Barbara.
+
+You write (omiting the history as to why you were changing latex.tex)
+>
+> Studying TeX the program I found what I think is an oversight:
+> whenever a glue node is generated, either when scanning a glue
+> specification in assignment, as well as in glue register arithmetic,
+> the procedure trap_zero_glue is called to replace references to zero
+> glue to a reference to the special object zero_glue.
+
+Actually, this is a bit too strong. |trap_zero_glue| is only called
+when setting a `glue register or parameter', as the preamble to section
+1229 says. For example, in
+
+ \setbox0=\hbox{Foo\hskip 0pt plus 0pt minus 0pt Bar}
+
+the glue node doesn't point to |zero_glue|, but to a private |glue_spec|
+with zero contents.
+
+> The only
+> exception to this rule is scanning the glue specification after
+> \tabskip in preparation of an alignment preamble. Therefore,
+>
+> \tabskip=\z@
+>
+> generates a new glue node with zero fields, whereas
+>
+> \tabskip=\z@skip
+>
+> generates only a reference to zero_glue.
+
+I agree. This breaks the invariant promised in #1229.
+[ dek -- ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+]
+
+> Now, since the overfull box
+> printer checks only for equivalence with zero_glue, a blank is printed
+> in the first case.
+
+[The code in |short_display| (section 175)]
+
+> The only other difference I could find is in TeX's
+> processing of alignment entries: in a certain case the tabskip glue
+> reference is replaced by zero_glue unless it is already zero_glue,
+> i.e. this code is executed without it really being necessary.
+
+I can find no way other than |short_display| of making the difference
+visible, which is why I call it a bugette rather than a bug. Some
+glue parameters are tested for being zero by pointer comparison with
+|zero_glue|, but \tabskip isn't one of them.
+
+> I cannot think of a reason why this behaviour should influence
+> anything other than the overfull box printing, yet I think it should
+[ dek -- also tracingparagraphs \S857
+]
+> be changed in the next update to tex.web. It seems to me that a simple
+> call to trap_zero_glue should suffice.
+
+Specifically, in |get_preamble_token|, section 782. There will need
+to be a forward declaration of |trap_zero_glue| as well.
+[ dek -- ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+]
+
+> What do you think?
+
+I think it should go on Barbara's list for Don.
+
+Chris Thompson
+-------
+Date: 28 Oct 1993 17:39:56 +0100
+From: schoepf@sc.ZIB-Berlin.DE (Rainer Schoepf)
+To: Chris Thompson <CET1@phx.cam.ac.uk>
+Cc: Barbara Beeton <BNB@MATH.AMS.ORG>, Rainer Schoepf <Schoepf@sc.ZIB-Berlin.DE>
+Subject: Re: [interesting effect in overfull box printout]
+
+Chris,
+
+I wrote:
+
+ > > The only other difference I could find is in TeX's
+ > > processing of alignment entries: in a certain case the tabskip glue
+ > > reference is replaced by zero_glue unless it is already zero_glue,
+ > > i.e. this code is executed without it really being necessary.
+
+to which you replied:
+
+ > I can find no way other than |short_display| of making the difference
+ > visible, which is why I call it a bugette rather than a bug.
+
+I agree.
+
+ > Some
+ > glue parameters are tested for being zero by pointer comparison with
+ > |zero_glue|, but \tabskip isn't one of them.
+
+But it is, in the piece of code labelled
+[ dek -- ---? that's _not_ a pointer comparison to zero_glue
+]
+
+ <Nullify |width(q)| and the tabskip glue following this column@>
+
+If I understand this correctly, the local variable s points to a copy
+of the tabskip glue of that point. But that doesn't influence the
+outcome in any way.
+-------
+Date: 28 Oct 1993 18:06:22 +0000 (GMT)
+From: Chris Thompson <CET1@phx.cam.ac.uk>
+To: Rainer Schoepf <Schoepf@sc.ZIB-Berlin.DE>
+Subject: Re: [interesting effect in overfull box printout]
+
+Rainer,
+
+> > Some
+> > glue parameters are tested for being zero by pointer comparison with
+> > |zero_glue|, but \tabskip isn't one of them.
+>
+> But it is, in the piece of code labelled
+>
+> <Nullify |width(q)| and the tabskip glue following this column@>
+>
+> If I understand this correctly, the local variable s points to a copy
+> of the tabskip glue of that point. But that doesn't influence the
+> outcome in any way.
+
+Maybe I expressed that wrongly. I meant that there were no cases of
+comparing \tabskip directly out of |equiv(glue_base+tab_skip_code)|
+with |zero_glue|, in the way that there is for \spaceskip and
+\xspaceskip in |main_control|, for example. The code in section 802
+that you mention is comparing glue copied from \tabskip (sharing its
+|glue_spec|, admittedly) and as you say it doesn't effect the outcome,
+as the test against the glue already being |zero_glue| is only an
+optimization and could be omitted entirely.
+
+Chris Thompson
+Internet: cet1@phx.cam.ac.uk
+JANET: cet1@uk.ac.cam.phx
+-------
+[ dek -- I hesitate to change anything here, on the off chance that I did
+ have a reason for the ``redundant'' code in \S802 ... something
+ way back in my memory warns me to leave this alone. I will just
+ change the slightly-false comment in \S1229.
+ Of course I am 99.9999% certain that I could safely make the
+ change you suggest, but it is a big pain to handle the forward
+ referencing [I probably would put \S1229 into a section of its
+ own named Declare the procedure trap_zero_glue, and place that
+ in 782.] -- requires reprinting many pages of the book. Much
+ too much trouble for very little gain at this late late stage.
+]
+
+ ----------------------------------------------------------------------
+
+ +++ font_mem_max and other memory parameters
+
+Date: 17 Dec 1993 16:01:52 -0500 (EST)
+From: Berthold Horn <71172.524@CompuServe.COM>
+Subject: Re: where to send bug report
+
+Dear Barbara:
+
+[...]
+
+[ dek * ]
+(1) OK, here it is. I don't know whether to call it a `real' bug since it
+only comes up if one implements Knuth's scheme for growing
+main memory in TeX (which is why TeX implementers haven't
+run into it before --- except possibly Barry Smith? with Textures).
+But then Knuth did describe how it is supposed to work...
+
+In 174 (page 71 of `TeX: the program') it should say:
+
+ begin while p \ne null do
+[ dek -- No this is not robust in the presence of clobbered lists -- You
+ are asking me to _undo_ one of the important corrections I made
+ years ago.
+]
+
+instead of:
+
+ begin while p > mem_min do
+
+On machines with fixed main memory (or in iniTeX), these happen to be
+equivalent because` mem_min' is zero, just as `null' is zero. But when
+[ dek -- ?? null is -30000 on my system at home, for instance.
+]
+memory grows downwards, then `mem_min' is negative, and one can get
+caught in a delightful infinite loop while looking for the null at the end of
+a list! The same problem occurs in 182 (page 74), Fortunately nowhere else.
+
+An alternate `fix' would be to redefine null to be the same as memmin,
+but that would be a very poor solution since in dynamic allocation,
+mem_min changes from time to time.
+
+(2) While I have your attention, I'd like to complain about a recent
+implementaiton decision
+that is a pain for dynamic memory allocation. For `bcharlabel' is used
+`fontmemptr'. For a system with fixed allocations, this is a reasonable
+[ dek - ^^^ size
+]
+way to say this doesn't point to any valid font, but its no good if font memory
+can grow. I replaced this with `maxhalfword', which is fixed. Plus, when a
+format file is read in, I try and figure out what value of fontmemptr was used
+when it was dumped and replace that with `maxhalfword'. Its important for
+a format file not too have too many frozen in dependencies on allocations.
+One should be able to handle at least variations in size of main memory,
+string pool size, font memory size, hyphenation table size etc.
+
+(3) By the way, I am wondering why we still seem to be using maxhalfword =
+262144
+when there aren't really any 36 bit machines left (been I while since I hacked
+ on a PDP6 or PDP10 :=), and everyone is using
+[ dek -- ^^^^^^^^ in fantasy land
+]
+64 bit words. Doesn't make sense in a 32 bit address space world...
+
+(4) Finally, I'd like to recommend that --- given that we are using 64 bit
+words ---
+the TeX 82 limitation in fontmax == 256 be lifted. We did this in Y&YTeX on
+[ dek -- ^^^^^^^^^
+ This would break the _Pascal_ implementation that still exists,
+ I think?
+]
+an experimental basis and it involves only a tiny change where font definitions
+are written to the DVI file, and a tiny change where font changes are written
+to the DVI file. DVI processors are already supposed to be able to
+understand the multi-byte font commands (despite the fact that TeX 82
+never generates them) - although, the `level 0' standard does allow them
+to support only 256 internal font numbers (a weird and wonderful contraction
+if you ask me).
+
+[...]
+[ dek -- These things are up to implementors' discretion.
+ Something in the back of my mind triggers a caution flag --
+ not only in the memory for hyphenation but also in the \span
+ feature of alignments, I fear (?) Good luck.
+]
+
+Berthold & Blenda.
+-------
+Date: 09 Mar 1994 16:59:50 -0500 (EST)
+From: andrew.trevorrow@anu.edu.au (Andrew K Trevorrow)
+Subject: new TeX bug
+
+Hi Barbara,
+
+I think I've found a bug in TeX. Please pass on the following note to the
+TeX implementors to verify my analysis.
+
+ ----------------
+
+Over the last couple of years a few OzTeX users have reported a strange bug
+in which a character at the start of a word changes for no obvious reason.
+I was never able to reproduce the problem until the other day when
+Ole Michael Selberg sent me the vital clue: the problem only happens if
+font_mem_size is increased and the format file is NOT rebuilt.
+(OzTeX users don't have to recompile TeX to change font_mem_size;
+they simply edit a number in a configuration file.)
+
+Now font_mem_size is supposed to be one of the parameters that can differ
+in INITEX and VIRTEX. The problem is that non_address is set to font_mem_size,
+so when bchar_label[f] values are set to non_address and stored in a format
+file by INITEX they will not be recognized as non-address values by a VIRTEX
+that uses a different font_mem_size!
+
+Note that if font_mem_size in VIRTEX is smaller than the INITEX value
+then a fatal format error will occur when loading bchar_label[nullfont]
+(which was set to non_address by INITEX). If font_mem_size in VIRTEX is
+larger than the INITEX value then far nastier problems can occur, such as
+a character at the start of a word changing.
+
+One solution would be to treat font_mem_size like hash_size and the other
+parameters that require format files to be rebuilt if their values change.
+A better solution is to set non_address to -1; this allows font_mem_size to
+be different in INITEX and VIRTEX. Here are the changes needed to tex.web:
+
+@x
+@!font_index=0..font_mem_size; {index into |font_info|}
+@y
+@!font_index=-1..font_mem_size; {index into |font_info|}
+@z
+[ dek -- Now many compilers will refuse to pack properly
+]
+
+@x
+@d non_address==font_mem_size {a spurious |font_index|}
+@y
+@d non_address==-1 {a spurious |font_index|}
+@z
+
+@x
+if bchar_label[hf]<non_address then {put left boundary at beginning of new line}
+@y
+if bchar_label[hf]<>non_address then {put left boundary at beginning of new line}
+@z
+
+@x
+undump(0)(font_mem_size)(bchar_label[k]);
+@y
+undump(non_address)(font_mem_size-1)(bchar_label[k]);
+@z
+
+I've included these changes in a new version of OzTeX and they fix the bug.
+
+Andrew Trevorrow
+akt150@huxley.anu.edu.au
+-------
+Date: 09 Mar 1994 11:08:17 -0500 (EST)
+From: Louis Vosloo <71172.524@CompuServe.COM>
+Subject: [andrew.trevorrow@anu.edu.au (Andrew K Trevorrow): new TeX bug]
+
+Dear Barbara:
+
+I believe I already reported on this problem. font_mem_max is used
+[ dek -- ^^^ size
+]
+as a special value for bchar etc. Which is fine if font_mem_max never
+changes, but for a `dynamic' TeX (like Y&YTeX) this doesn't work.
+
+My solution was to change this to max_half_word.
+
+In addition, my format undumping code tries to figure out
+what value was used in the dumped format and then replaces that
+systematically with max_half_word.
+That way it can handle `old' format files made before the fix as well.
+
+Berthold K.P. Horn
+71172.524@compuserve.com
+-------
+Date: 09 Mar 1994 11:25:40 -0500 (EST)
+From: Berthold Horn <71172.524@CompuServe.COM>
+Subject: [andrew.trevorrow@anu.edu.au (Andrew K Trevorrow): new TeX bug]
+
+Dear Barbara:
+
+The following is extracted from email I sent to you on 93/Dec/17.
+The bug reported by Trevor is mentioned below in item (2)
+
+Regards, Berthold.
+
+...
+
+(1) OK, here it is. I don't know whether to call it a `real' bug since it
+only comes up if one implements Knuth's scheme [...]
+
+ [ remainder of message as above ]
+-------
+Date: 09 Mar 1994 17:02:14 +0000 (GMT)
+From: Chris Thompson <CET1@phx.cam.ac.uk>
+To: Barbara Beeton <BNB@MATH.AMS.ORG>
+Cc: Andrew Trevorrow <andrew.trevorrow@anu.edu.au>
+Subject: Andrew Trevorrow's new TeX bug
+
+Barbara,
+
+ I am replying directly to you rather than to the tex-implementors list,
+with a copy to Andrew.
+
+> ... as soon as the problem has
+> been verified, i'll forward it to knuth. (it's getting to be
+> time for his annual tex-inspection tour.)
+[ dek -- ^^^^^^
+ exponentially decreasing, actually, although I am one year
+ behind plan (not two)
+]
+
+About time :-) It gets later every year...
+[ dek -- \check
+]
+
+> Now font_mem_size is supposed to be one of the parameters that can differ in
+> INITEX and VIRTEX. The problem is that non_address is set to font_mem_size,
+> so when bchar_label[f] values are set to non_address and stored in a format
+> file by INITEX they will not be recognized as non-address values by a VIRTEX
+> that uses a different font_mem_size!
+>
+> Note that if font_mem_size in VIRTEX is smaller than the INITEX value
+> then a fatal format error will occur when loading bchar_label[nullfont]
+> (which was set to non_address by INITEX). If font_mem_size in VIRTEX is
+> larger than the INITEX value then far nastier problems can occur, such as
+> a character at the start of a word changing.
+
+Yes, this is a bug, and a quite nasty one too. Introduced by the changes
+in TeX version 3, so presumably Andrew only gets the smaller reward.
+[ dek -- (Berthold)
+]
+
+> One solution would be to treat font_mem_size like hash_size and the other
+> parameters that require format files to be rebuilt if their values change.
+> A better solution is to set non_address to -1; this allows font_mem_size to
+> be different in INITEX and VIRTEX.
+
+Putting |non_address| at the other end of the range seems to be the
+right solution. I think it could equally well be set to 0 as to -1.
+[ dek -- ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+]
+The values in the |bchar_label| array can never be this small naturally:
+they are true indices into |font_info| rather than offset ones.
+
+There is a technical problem about making this change to TeX. One needs
+[ dek -- ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+]
+to force old format files to be invalid, because the |non_address|
+values in them would be wrongly interpreted (even more so than at
+present, that is!). This wouldn't happen "naturally".
+
+My MVS version of TeX has hacks to make |font_index| a signed 16-bit
+value, starting at |font_mem_base| (currently dumped in the format file)
+rather than zero. I can foresee myself having to rework this...
+
+Chris Thompson
+Cambridge University Computing Service
+-------
+Date: 09 Mar 1994 13:04:02 -0500 (EST)
+From: bbeeton <BNB@MATH.AMS.ORG>
+To: CET1@phx.cam.ac.uk
+Cc: BNB@MATH.AMS.ORG, andrew.trevorrow@anu.edu.au
+Subject: Re: Andrew Trevorrow's new TeX bug
+
+chris and andrew,
+berthold horn has reminded me that he reported this bug in december;
+i did forward his message to you then, chris, but it seems to have
+got lost. attached is the forwarded message, along with some of
+today's commentary from berthold. he avers that setting non_address
+to -1 won't work under certain circumstances, and proposes another
+solution that does work for him.
+
+this seems to be more contentious than i expected. perhaps a wider
+discussion is warranted -- i've already received (but not read)
+a few other messages on the subject, including one from peter
+breitenlohner.
+cheers. -- bb
+ --------------------
+
+Date: 17 Dec 1993 16:27:33 -0500 (EST)
+From: bbeeton <BNB@MATH.AMS.ORG>
+To: cet1@cus.cam.ac.uk
+Subject: [Berthold Horn <71172.524@CompuServe.COM>: Re: where to send bug
+ report]
+
+chris,
+would appreciate it if you could verify this bug report, and
+perhaps comment on the other points made in the message.
+
+best wishes for the holidays.
+ -- bb
+ ---------------
+
+Date: 17 Dec 1993 16:01:52 -0500 (EST)
+From: Berthold Horn <71172.524@CompuServe.COM>
+To: bbeeton <BNB@MATH.AMS.ORG>
+Subject: Re: where to send bug report
+
+Dear Barbara:
+
+[...]
+
+(1) OK, here it is. I don't know whether to call it a `real' bug since it
+only comes up if one implements Knuth's scheme [...]
+
+ [ remainder of message as above ]
+
+ --------------------
+
+Date: 09 Mar 1994 11:08:17 -0500 (EST)
+From: Berthold Horn <71172.524@CompuServe.COM>
+To: bbeeton <BNB@MATH.AMS.ORG>
+Subject: [andrew.trevorrow@anu.edu.au (Andrew K Trevorrow): new TeX bug]
+
+Dear Barbara:
+
+I believe I already reported on this problem. font_mem_max is used
+as a special value for bchar etc. Which is fine if font_mem_max never
+changes, but for a `dynamic' TeX (like Y&YTeX) this doesn't work.
+
+My solution was to change this to max_half_word.
+
+In addition, my format undumping code tries to figure out
+what value was used in the dumped format and then replaces that
+systematically with max_half_word.
+That way it can handle `old' format files made before the fix as well.
+
+Berthold K.P. Horn
+71172.524@compuserve.com
+-------
+Date: 09 Mar 1994 18:39:51 +0000 (GMT)
+From: Peter Breitenlohner <PEB%DMUMPIWH.BITNET@vm.gmd.de>
+To: bbeeton <BNB@MATH.AMS.ORG>
+Subject: Re: [andrew.trevorrow@anu.edu.au (Andrew K Trevorrow): new TeX bug]
+
+Barbara,
+1. this is definitely a bug
+2. The fix is no good (incomplete). There is at least one place in
+ tex.web which now says
+ if bchar_label[hf]<non_address
+ and changing non_address from very large too very small requires a change
+ here too (I'll check if there are more places)
+3. I dislike the change of font_index=0..font_mem_size into
+ font_index=-1..font_mem_size because on some systems that may have
+ the effect that 4 bytes instead 2 bytes are required for a font_index
+4. I think one can safely set non_address=0 but I have to check that
+ and will send you a complete fix tomorrow.
+5. I will also reformulate my "bug or design feature" msg from some
+ time ago and would like to ask you to forward it to don.
+regards Peter
+-------
+(reply, 09 Mar 1994)
+thanks much, peter.
+[ forwarded all previous mail to peter ]
+-------
+Date: 09 Mar 1994 11:51:32 -0800 (PST)
+From: drf@frame.com (David Fuchs)
+Subject: Re: [andrew.trevorrow@anu.edu.au (Andrew K Trevorrow): new TeX bug]
+
+I'd forward it along to dek; [...]
+
+ -drf
+-------
+(reply, 09 Mar 1994)
+what's becoming clear about this particular bug is that it impinges
+on some of the system-dependent areas, in particular, how various
+implementors choose to implement the ability to change the size of
+various memory blocks at run time. since more implementations do
+have that ability now than formerly, and they all seem to be
+implemented differently (though not all techniques are public),
+this is potentially a rats nest. so information is important not
+only on what the bug is and how you can make it happen, but what
+else is related and where it might go wrong if fix x is adopted.
+i think the present participants are capable of doing a pretty
+thorough job.
+-------
+Date: 10 Mar 1994 11:27:26 +0000 (GMT)
+From: Peter Breitenlohner <PEB%DMUMPIWH.BITNET@vm.gmd.de>
+To: Barbara Beeton <bnb@MATH.AMS.ORG>,
+ Chris Thompson <cet1@phoenix.cambridge.ac.uk>,
+ Andrew Trevorrow <andrew.trevorrow@anu.edu.au>,
+ Berthold Horn <71172.524@compuserve.com>
+Subject: andrews bug et alia
+
+hi barbara (and chris, andrew, berthold),
+thanks for sending the various remarks, here my comments.
+
+1. andrews bug
+yes, this definitely is a bug [...] since font_mem_size
+is among those parameters that are explicitely allowed to differ between
+VIRTEX and INITEX.
+
+andrews fix is bad for two reasons
+ a) the test ...<non_addres must be changed into ...>non_address
+ b) a bchar_label=-1 fails in undump where the value is tested to be
+ in the range 0..font_mem_size.
+I did not think about Chris's point (invalidating old format files) but
+had changed the test in undump anyway (general neatness) and this pays
+[ dek - ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+]
+nicely since it does catch the old formats that must be rebuilt when
+non_address is changed from font_mem_size to 0 (not -1) as I would
+recommend.
+
+I fully agree with Chris that non_address=0 is OK, and I strongly dislike
+the -1 for various reasons (among others it unnecessarily forces font_index
+to be signed instead of unsigned).
+
+I have looked into tex.web and am fully convinced that one can
+safely set non_address=0 since font_info[0] is occupied
+by the first of \nullfont's parameters.
+
+Here my proposed change:
+
+@x [30] m.549 l.10678 - bug fix
+@d non_address==font_mem_size {a spurious |font_index|}
+@y
+@d non_address==0 {a spurious left boundary char label}
+@z
+%---------------------------------------
+@x [41] m.916 l.17965 - bug fix
+if bchar_label[hf]<non_address then {put left boundary at beginning of new line}
+@y
+if bchar_label[hf]>non_address then {put left boundary at beginning of new line}
+@z
+%---------------------------------------
+@x [50] m.1323 l.24036 - bug fix
+undump(0)(font_mem_size)(bchar_label[k]);
+@y
+undump(0)(fmem_ptr)(bchar_label[k]);
+[ dek -- ^^ -1
+]
+@z
+%---------------------------------------
+
+2. berthold horns msg from Dec 17
+ad 2: non_address=max_halfword is probably OK as well, I have not checked
+all implications. I prefer =0 and this has the definite advantage that it
+does catch old formats that need to be rebuilt. (Having to rebuild formats
+when the program changes - even if the pool checksum doesn't change -
+is certainly ok.)
+
+ad 3: that is entirely up to implementors, the 262144 never shows up in
+tex.web. But bigTeX has to set some reasonable limit on the size of
+the mem array otherwise a stupid paging system uses up enormous amounts of
+paging space and non-paging systems are completely sunk.
+Cetainly 256K is as good as any other number of the right size.
+
+ad 4: It would be tempting to increase font_max once max_halfword and
+max_quarterword have been increased. TeX uses at present only one-byte
+font numbers in the DVI file, i.e., range 0..255. Clearly TeX's dvi writing
+routines could certainly be adapted to a larger range, no problem here.
+But: Extending this range may have implications on existing DVI software.
+Some DVI drivers may rely on one-byte font numbers (re: driver standard?).
+Therefore I would be very careful at this point!!
+
+ad 1: I can't understand this problem. In VIRTEX mem_min must be <=mem_bot,
+[ dek -- Might have lots of stuff between mem_bot and mem_min, with a
+ special allocation scheme
+]
+and mem_min>=min_halfword=null. Now mem_bot is a glue spec, hence can never
+occur when traversing a list. If mem_min is mem_bot-1 or mem_bot-2 the one
+or two extra words are never used and if mem_min<mem_bot-2 then mem[mem_min]
+is also never used (done in undump memory). Hence the word mem[mem_min]
+is either a glue spec or unused. This can never give a problem
+with tests such as p>mem_min when traversing lists.
+It might be nicer to test for p<>null but I think this is no bug.
+Maybe only don knows why he has formulated this one test in a different way,
+but probably he forgotten the reasoning behind that.
+
+A bug might creep in
+if someone is dynamically extending the mem array during the run of
+VIRTEX and is not doing it properly (mimicking the behaviour of undump).
+I would say any problems introduced here are due to improper sys-dep
+modifications.
+[ dek -- \check
+]
+
+regards peter
+-------
+Date: 10 Mar 1994 12:57:35 +0000 (GMT)
+From: Chris Thompson <CET1@phx.cam.ac.uk>
+To: Barbara Beeton <BNB@MATH.AMS.ORG>
+Cc: Andrew Trevorrow <andrew.trevorrow@anu.edu.au>,
+ Peter Breitenlohner <PEB@DMUMPIWH.EARN>,
+ Berthold Horn <71172.524@CompuServe.COM>
+Subject: Re: Andrew Trevorrow's new TeX bug
+
+Barbara,
+
+> berthold horn has reminded me that he reported this bug in december;
+> i did forward his message to you then, chris, but it seems to have
+> got lost.
+
+I found this message in an archive. Apologies: it arrived too late
+to be dealt with before Christmas, and got completely forgotten
+afterwards. If you have anything else outstanding on the potential
+bug list that I haven't replied to you about, please remind me a.s.a.p.
+
+> this seems to be more contentious than i expected. perhaps a wider
+> discussion is warranted -- i've already received (but not read)
+> a few other messages on the subject, including one from peter
+> breitenlohner.
+
+I agree with Peter Breitenlohner (personal communication) and with
+Bernd Raichle (in tex-implementors): there is absolutely no doubt
+that this is a bug. I don't think Wayne's position is defensible:
+I will post something to tex-implementors saying so.
+
+The main thing is to make sure the bug report is on the list for
+Don. We could argue about the merits of particular ways of fixing
+it until the cows come home, but it is Don who will actually make
+that decision.
+
+Peter, Andrew and I all seem happy with |non_address| = 0. Peter
+writes
+
+> ... I strongly dislike the -1 for various reasons (among others it
+> unnecessarily forces font_index to be signed instead of unsigned).
+
+(Although an alternative would be to make |bchar_label| an |integer|
+array rather than a |font_index| one.)
+
+Berthold suggests |non_address| = |max_halfword|, but I think this is
+not portable. While many implementations may squeeze |font_index|
+values into halfwords (indeed, I do myself) there is nothing in tex.web
+to prevent |font_mem_size| from being larger than |max_halford|.
+[ dek -- ^^ w
+]
+(There is curiosity, though: |font_params| is an array of |halfword|s.
+Can one break TeX by setting \fontdimen<amazingly large number>? I will
+have to think about that one.)
+[ dek * ]
+
+I didn't intend my point about forcing the invalidation of old format
+files to be a big issue (there are many ways to achieve the desired
+effect): just something not to be forgotten. Andrew writes:
+
+> Maybe it would be a good idea to put some sort of version number (the
+> current TeX version?) in format files. I wonder if there is a spot
+> that would be guaranteed to catch all old formats? A suitable error
+> message would be "This is an old format file; use INITEX to rebuild
+> it.".
+
+It shouldn't be the TeX version number, because sometimes a version
+change does not require new format files, which is convenient when
+it happens. I have in the past fiddled with the 69069 at the end of the
+file to achieve deliberate invalidation in local implementations, but
+to get something like Andrew's message consistently one would want
+something right at the beginning.
+
+To take Berthold's 4 sections in order:
+
+1. The |null| test. (I suspect that this is the only part of the message
+ I even glanced at in December.) My first inclination is to agree with
+ Peter's analysis, but I need to go through this in detail again. I
+ will let you know.
+
+2. = Andrew's bug, discussed above.
+
+3. Why not |max_halfword| > 262144 ? This is a question relating to
+ a particular implementation.
+
+4. Why not |font_max| > |font_base| + 256 ? I have wondered about that
+ myself. I don't think I can improve on Peter's analysis:
+
+> It would be tempting to increase font_max once max_halfword and
+> max_quarterword have been increased. TeX uses at present only
+> one-byte font numbers in the DVI file, i.e., range 0..255. Clearly
+> TeX's dvi writing routines could certainly be adapted to a larger
+> range, no problem here.
+> But: Extending this range may have implications on existing DVI
+> software. Some DVI drivers may rely on one-byte font numbers (re:
+> driver standard?). Therefore I would be very careful at this point!!
+
+No harm in suggesting it to Don, I suppose. If he doesn't like it,
+it is always open to an implementor to provide this extension via
+the change file.
+[ dek -- right ... see also \span (?)
+]
+
+Chris Thompson
+Cambridge University Computing Service
+-------
+Date: 10 Mar 1994 14:09:12 +0000 (GMT)
+From: Peter Breitenlohner <PEB%DMUMPIWH.BITNET@vm.gmd.de>
+To: Berthold Horn <71172.524@CompuServe.COM>
+Cc: Barbara Beeton <bnb@MATH.AMS.ORG>,
+ Chris Thompson <cet1@phoenix.cambridge.ac.uk>
+Subject: Re: andrews bug et alia
+
+On 10 Mar 94 08:03:11 EST you said:
+>
+>Believe me, this very definitely *is* a bug! Think about what happens when
+>you extend the variable length node list downward. You can't very well then
+>go back over all list structures and change `null' to the new `mem_min'!
+>
+>> A bug might creep in if someone is dynamically extending the mem array
+>> during the run of VIRTEX and is not doing it properly (mimicking the
+>> behaviour of undump). I would say any problems introduced here are due to
+>> improper sys-dep modifications.
+>
+I think whenever you are dynamically allocating more mem-memory you should
+1. never have mem_min<min_halfword=null and
+[ dek - ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+ Absolutely true (see \S116)
+]
+2. should never use mem[mem_min] (whatever the present mem_min value) unless
+ your proposed code change is made
+3. never ever use mem[min_halfword].
+I agree a change in mod 174 ( p>mem_min => p<>null ) would be desirable
+[ dek -- no, it could cause p to go outside the array bounds.
+]
+and would make life a little easier for those who want/have to dynamically
+enlage mem at the low end. I only disagree that this can be called a bug.
+The only point where standard TeX enlarges the low end of mem is when
+a format is read and VIRTEX's mem_min is below INITEX's mem_bot.
+And for this case Knuth's coding works fine, hence no bug
+[ dek -- _NB_: show_mode_list, short_display are designed to avoid
+ crashing the system when TeX is buggy. See comment in \S182
+]
+
+regards peter
+-------
+Date: 12 Mar 1994 12:30:55 +0000 (GMT)
+From: Peter Breitenlohner <PEB%DMUMPIWH.BITNET@vm.gmd.de>
+To: Andrew K Trevorrow <andrew.trevorrow@anu.edu.au>,
+ Barbara Beeton <bnb@MATH.AMS.ORG>
+Subject: Re: andrews bug et alia
+
+Hi Andrew, Barbara
+On Sat, 12 Mar 94 14:14:40 EST you (andrew) said:
+>
+>By the way, I think that in your change to undump you should use
+>fmem_ptr-1 rather than just fmem_ptr (which is the first UNUSED index
+>in the font_info array).
+>
+To Andrew: That is indeed a good idea since it would catch old formats even
+in the rare event that fmem_ptr=font_mem_size!
+[ dek -- Actually I once noticed that "Web2C" omits the checking ...
+ We must make sure this test is _not_ skipped.
+]
+>
+To Barbara: can you please append the above to my messsage with the proposed
+fix.
+>
+regards peter
+-------
+Date: 10 Mar 1994 17:03:39 +0000 (GMT)
+From: Chris Thompson <CET1@phx.cam.ac.uk>
+To: Barbara Beeton <BNB@MATH.AMS.ORG>
+Cc: Andrew Trevorrow <andrew.trevorrow@anu.edu.au>,
+ Peter Breitenlohner <PEB@DMUMPIWH.EARN>,
+ Berthold Horn <71172.524@CompuServe.COM>
+Subject: Small TeX bug - \fontdimen <large-number>
+
+Barbara,
+
+I wrote:
+> (There is curiosity, though: |font_params| is an array of |halfword|s.
+> Can one break TeX by setting \fontdimen<amazingly large number>? I will
+> have to think about that one.)
+
+There is, in fact, a bug here. The following code in TeX section 580,
+part of |find_font_dimen|,
+
+ begin repeat if fmem_ptr=font_mem_size then
+ overflow("font memory",font_mem_size);
+ font_info[fmem_ptr].sc:=0; incr(fmem_ptr); incr(font_params[f]);
+ until n=font_params[f];
+
+contains no precautions to prevent |font_params[f]| from being
+incremented from |max_halfword|, its largest legal value. What
+happens next is implementation-dependant. In the case of the one
+I was experimenting with, |halfword| values wrap quietly from
+|max_halfword| to |min_halfword|, and so (for large enough |n|)
+the loop test is never satisfied, and one gets a font memory
+overflow condition (which is only mildly spurious).
+
+Possible fixes: make |font_params| an array of |integer|, or
+|font_index| (maybe: not sure about this), instead of |halfword|.
+Alternatively, in section 578 replace
+
+ if n<=0 then cur_val:=fmem_ptr
+
+by
+
+ if (n<=0) or (n>max_halfword) then cur_val:=fmem_ptr
+
+Chris Thompson
+Cambridge University Computing Service
+-------
+Date: 12 Mar 1994 12:47:28 +0000 (GMT)
+From: Peter Breitenlohner <PEB%DMUMPIWH.BITNET@vm.gmd.de>
+To: Chris Thompson <CET1@PHOENIX.CAMBRIDGE.AC.UK>
+Subject: Re: Small TeX bug - \fontdimen <large-number>
+
+On Thu, 10 Mar 94 17:03:39 GMT you said:
+>Barbara,
+>
+>I wrote:
+>> (There is curiosity, though: |font_params| is an array of |halfword|s.
+>> Can one break TeX by setting \fontdimen<amazingly large number>? I will
+>> have to think about that one.)
+>
+>There is, in fact, a bug here. The following code in TeX section 580,
+>part of |find_font_dimen|,
+>
+> begin repeat if fmem_ptr=font_mem_size then
+> overflow("font memory",font_mem_size);
+> font_info[fmem_ptr].sc:=0; incr(fmem_ptr); incr(font_params[f]);
+> until n=font_params[f];
+>
+>contains no precautions to prevent |font_params[f]| from being
+>incremented from |max_halfword|, its largest legal value. What
+>happens next is implementation-dependant. In the case of the one
+>I was experimenting with, |halfword| values wrap quietly from
+>|max_halfword| to |min_halfword|, and so (for large enough |n|)
+>the loop test is never satisfied, and one gets a font memory
+>overflow condition (which is only mildly spurious).
+>
+>Possible fixes: make |font_params| an array of |integer|, or
+>|font_index| (maybe: not sure about this), instead of |halfword|.
+>Alternatively, in section 578 replace
+>
+> if n<=0 then cur_val:=fmem_ptr
+>
+>by
+>
+> if (n<=0) or (n>max_halfword) then cur_val:=fmem_ptr
+>
+Hi Chris,
+1. I agree this is a bug and (from past experience) I would say you are due
+for a cheque (a big one). Assuming font_mem_size>max_halfword the program may
+[ dek -- $327.68
+]
+attempt to assign a value >max_halfword to font_params[f]. If range checking
+were on (who is nowadays running TeX with range checking on?) this would give a
+"high bound violation" or however this is called in a particular systems.
+Knuth has always classified such as bugs. (I once got a cheque for an even
+more obscure range checking error.)
+
+As to a fix I have convinced myself that defining
+ @!font_params:array[internal_font_number] of font_index; {how many font
+solves all problems and introduces no new ones.
+In particular I have verified with a `virgin INITEX' with font_mem_size=32767
+that one can say "\fontdimen 32767 \nullfont" with no problems whereas
+ "\fontdimem 32768 \nullfont" leads to an overflow [font_mem... .
+Hence TeX makes sure that font_params[f] is allways in the range
+7..font_mem_size, i.e., a subset of font_index.
+
+As to the other possibilities: your alternative
+> if (n<=0) or (n>max_halfword) then cur_val:=fmem_ptr
+is not so good since the result is implementation dependent, on some
+systems you can use \fontdimen n f with some very large n and on other
+systems (or the same system with different switches) you can't.
+I think Knuth's policy for such was that an error is not sufficient,
+only a fatal error is good enough indication.
+And whoever wants to set \fondimen 32000 f is probably out of his mind
+anyway.
+
+2. Did you already have a chance to look at the e-TeX files ?
+
+regards peter
+-------
+
+<<< end The TeX program
+
+************************************************************************