Rounding to an uncertainty larger than the digits with siunitx

Question

I have a problem with the siunitx package. In some cases the rounding is not correct (the position of the comma is not correct, see in the MWE I provided below).

Do you have any suggestions?

\documentclass[12pt, a4paper]{scrartcl}

\usepackage{siunitx}
\sisetup{round-mode=uncertainty, uncertainty-mode = separate, round-precision=3}

\begin{document}
Hello, this is a test with the package siuntix:

\num{0.478747 \pm 0.231349} (correct rounding)

\num{0.266548 \pm 10.8466}

The correct output should be instead: 0.3\,\pm \,10.8
\end{document}

Answer 1

The next release of siunitx will check that there are enough digits to give a non-zero result on rounding to uncertainty. For the present, use:

\cs_gset:Npn \__siunitx_number_round_uncertainty:nnn #1#2#3
  {
     \__siunitx_number_round_uncertainty_check:nnnw {#1} {#2} {#3}
       #1#2 \q_recursion_tail \q_recursion_stop
  }
\cs_new:Npn \__siunitx_number_round_uncertainty_check:nnnw #1#2#3#4
  {
    \quark_if_recursion_tail_stop_do:Nn #4 { { 0 } { } { } }
    \int_compare:nNnTF {#4} = 0
      { \__siunitx_number_round_uncertainty_check:nnnw }
      { \__siunitx_number_round_uncertainty_check:Nnnnw #4 }
        {#1} {#2} {#3}
  }
\cs_new:Npn \__siunitx_number_round_uncertainty_check:Nnnnw #1#2#3#4#5
  \q_recursion_tail \q_recursion_stop
  {
    \int_compare:nNnTF { \tl_count:n {#1#5} } < { \tl_count:n {#4} }
      { { 0 } { } { } }
      {\__siunitx_number_round_uncertainty_aux:nnn {#2} {#3} {#4} }
  }
\cs_gset:Npn \__siunitx_number_round_uncertainty_aux:nnn #1#2#3
  {
    \exp_args:Nf \__siunitx_number_round_uncertainty:nnnn
      {
        \int_eval:n
          { \tl_count:n {#3} - \l__siunitx_number_round_precision_int }
      }
      {#1} {#2} {#3}
  }

(Note that this does not give your 'expected' result, which is wrong as the uncertainty is such that there is no useful value in the data.)