[pdftex] pdftex deterministic?

Reinhard Kotucha reinhard.kotucha at web.de
Tue Apr 3 22:19:52 CEST 2007

>>>>> "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.

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.

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.


Reinhard Kotucha			              Phone: +49-511-4592165
Marschnerstr. 25
D-30167 Hannover	                      mailto:reinhard.kotucha at web.de
Microsoft isn't the answer. Microsoft is the question, and the answer is NO.

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