[luatex] pdfdecimaldigits < 4

David Carlisle d.p.carlisle at gmail.com
Tue Jan 19 13:18:52 CET 2016

If pdfdecimal digits is set less than 4 the it appears that you get a

warning  (pdf backend): forcing decimal digits to 4

The manual could mention in the documentation of pdf.setdecimaldigits that
if set low then although
pdf.getdecimaldigits() will return the lower number, the effective value
will be 4 (if that is what happens?)

This came up as texlive 2015 shared pdftex/luatex format ini files set


in /usr/local/texlive/2015/texmf-dist/tex/generic/config/pdftexconfig.tex

so having translated that to
\pdfvariable decimaldigits=4

we get a warning in every (plain and latex) document.

So we could change the default to 4 but that would change pdftex as well
(in the currently suggested setup for texlive 2016 which uses a shared
Or we could separate the setup and use different values for pdftex and

So to help decide could you say why the minimum value of 4 was chosen, is
there a problem with 3 that we ought to definitely use 4 also in pdftex?
If not, could luatex allow 3?

Either way could the manual mention that setting the value low gives a

(Would it be possible for pdf.setdecimaldigits() to refuse to set the lua
value to
a low value, so that pdf.getdecimaldigits() always returns the effective
value that will be used?)

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