[pdftex] pdftex deterministic?

Matteo Centonza matteo at metatype.it
Wed Apr 4 10:54:27 CEST 2007

On Tue, 2007-04-03 at 22:19 +0200, Reinhard Kotucha wrote: 
> >>>>> "Matteo" == Matteo Centonza <matteo at metatype.it> writes:
>   > Using checksums is the cheapest way of comparing two files (even
>   > cheaper than a byte comparison) and give you absolute confidence
>   > on the result.
> Yes, but a PDF file contains a time stamp.  Hence you cannot produce
> two PDF files which have the same checksum.
> Even if you could force pdftex to create two files with the same
> timestamp, you'll get different checksums if you compare the output of
> pdftex 1.30 and pdftex 1.40, while what you see on screen is absolutely
> the same.

hi Reinhard,

probably you missed some bits:


In my case i'm comparing PDFs generated by the same binary application,
and maybe what you see on screen is not "absolutely" the same, it is
indeed, under your requirements.

> I assume that the only way to compare PDF files is to compare bitmaps.
> Of course, you can compare files with a resolution of one scaled point
> unless you are running MS-DOS or something derived from it.  Even with
> a finite amount of memory.  You don't have to to create bitmaps of the
> whole page.  You can run two processes at the same time which convert
> the PDF files to bitmaps and compare them line-by-line where the
> height of each line is one scaled point.

well, that's just one way of doing the comparison. Under different
conditions, you can find different algorithms.
> I don't see any problems here though I fear that such a program will
> not provide a result within a few seconds.  You have to be very patient.

i'm generally a patient guy ;)

But not when i'd like to provide a networked production system
with timings in the magnitude of a latex compile.

Thanks for your response,


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