Re: etex and pdftex have diverging memory constraints?

> Le 27 août 2025 à 15:59, Jim Diamond <[email protected]> a écrit :
> 
> On Wed, Aug 27, 2025 at 15:15 (+0200), jfbu via tex-live wrote:
> 
>> Hi,
> 
>> Sorry if this is very basic, but I always thought the sole difference between etex and pdftex is that the former works to produce a dvi and the latter a pdf.
> 
>> So, I was surprised to discover (or perhaps I observed that years ago and forgot) that pdftex has slightly more constrained memory constraints on macro expansion.
> 
>> Here is a test file testxintLength.tex
> 
>> ----
>> \input xintkernel.sty
>> \edef\x{\romannumeral\xintreplicate{%     
>> 2492679%
>> }{F}}
>> \expandafter\xintLength\expandafter{\x}
>> \bye
>> ----
> 
>> (the code creates a macro \x expanding to 2492679 F's then attempts to measure how many F's there are).
> 
>> Compilation with etex succeeds  (even with 2492694 in place of 2492679).
> 
>> $ etex testxintLength.tex
>> This is pdfTeX, Version 3.141592653-2.6-1.40.28 (TeX Live 2025) (preloaded format=etex)
>> restricted \write18 enabled.
>> entering extended mode
>> (./testxintLength.tex (./xintkernel.sty) [1] )
>> Output written on testxintLength.dvi (1 page, 216 bytes).
>> Transcript written on testxintLength.log.
> 
>> But compilation with pdftex fails.
> 
>> $ pdftex testxintLength
>> This is pdfTeX, Version 3.141592653-2.6-1.40.28 (TeX Live 2025) (preloaded format=pdftex)
>> restricted \write18 enabled.
>> entering extended mode
>> (./testxintLength.tex (./xintkernel.sty)
>> ! TeX capacity exceeded, sorry [main memory size=5000000].
>> <inserted text> 2492679
>>                        \xintlength ...xint_c_i \xint_c_ \xint_bye \relax                                                     l.5 \expandafter\xintLength\expandafter{\x}
>>                                            !  ==> Fatal error occurred, no output PDF file produced!
>> Transcript written on testxintLength.log.
> 
>> I am a bit surprised because I can not connect the constraints on TeX macro expansion with the output format DVI or PDF.  Needless to say I am completely ignorant of the innards.
> 
> Pdftex works fine on this example (Slackware64 15.0), at least in the sense
> that pdftex runs to completion.  The output PDF doesn't show the F's, at
> least with the viewer I tried.
> 
> Perhaps if you mention what OS you are using some additional help might be
> forthcoming.


Hello I am on macOS (as Herbert who also says the file compiles on his system).

The output PDF will contain simply the number 2492679 and the page number.

On my machine I have confirmed via modifying main_memory  in texmf.cnf and recompiling the etex and pdftex formats that the limits (a bit lower for pdftex) are about half the value of main_memory parameter.

I am intrigued by yours and Herbert report that compilation succeeds. I was working with the dev version of xint, but the used macros have had no modification but to be sure I checked out the 1.4m from 2022 which is last release and as expected I got same result.

It is unavoidable that a crash occurs with etex/pdftex if the 2492679 is replaced by some large enough number, so if you have time to waste on this you can try to set it to a higher value.

I am surprised the upper limit at my locale is lower than what you and Herbert experiment... and Herbert confirmed being with TL default memory settings like myself.

Kind regards


Jean-François