Automatically display the year as "b.C" (before Christ) if the value is negative?

Question

Is there any package that can automatically display the year as "b.C" (before Christ) if the value is negative?

I've code for that, but I am looking for a more elegant solution, or even better a package that would do this automatically. My solution also seems to generate an extra space afterwards.

I've look through siunitx and datetime2 but none seem to work like I need.

I am using the following (for Portuguese):

\newcommand{\byear}[1]{%
    \ifnum #1<0
    {-#1} a.C.\
    \else
    {#1} d.C.\
    \fi
}

Answer 1

Using \number to negate the input, and \@ to force a normal . not end of sentence, without adding extra space.

\documentclass{article}
\newcommand{\byear}[1]{%
    \ifnum #1<0
    {-#1} a.C.\
    \else
    {#1} d.C.\
    \fi
}

\newcommand{\bbyear}[1]{%
    \ifnum #1<0
    \number-#1\ a.C.\@%
    \else
    #1\ d.C.\@%
    \fi
}
\begin{document}

\byear{100}  \byear{-100} \byear{55}

\bbyear{100}  \bbyear{-100} \bbyear{55}



\end{document}