Tests for fpu magic

batty.tex

\documentclass[border=10pt]{standalone}
\usepackage[RPvoltages]{circuitikz}
\usetikzlibrary{fpu}
\makeatletter
\pgfqkeys{/pgf}{
    fpu/install only/.code={
        \pgfmath@warning{The key `/pgf/fpu/install only' is experimental and might %
            change or disappear at any point!}%
        \edef\pgf@list{#1}%
        \pgfutil@for\pgf@temp:=\pgf@list\do{%
            \expandafter\pgfmath@float@install@singlefunction\expandafter{%
                \romannumeral-`0\expandafter\pgfutil@trimspaces\expandafter{\pgf@temp}}%
        }%
    },
}

\def\pgfmath@float@install@singlefunction#1{%
    \ifcsname pgfmath@function@#1\endcsname\else
        \pgfmath@error{The function `#1' does not exist}{}%
    \fi
    \pgfmath@toks={}%
    \pgfmathloop
    \ifnum\pgfmathcounter>\csname pgfmath@operation@#1@arity\endcsname\relax%
    \else
        \expandafter\pgfmath@addto@toks\expandafter{\pgfmath@char@hash}%
        \expandafter\pgfmath@addto@toks\expandafter{\pgfmathcounter}%
    \repeatpgfmathloop
    \edef\pgfmath@head{\noexpand\def\expandafter\noexpand\csname pgfmath#1@\endcsname\the\pgfmath@toks}%
    \pgfmath@toks={}%
    \def\pgfmath@arguments{}%
    \pgfmathloop
    \ifnum\pgfmathcounter>\csname pgfmath@operation@#1@arity\endcsname\relax%
    \else
        \pgfmath@addto@toks{\pgfmathfloatparsenumber}%
        \expandafter\expandafter\expandafter\pgfmath@addto@toks
            \expandafter\expandafter\expandafter{\expandafter\expandafter\expandafter
                {\expandafter\pgfmath@char@hash\pgfmathcounter}}%
        \pgfmath@addto@toks{\let}%
        \expandafter\pgfmath@addto@toks\expandafter{%
            \csname pgfmath@argument@\pgfmathcounter\endcsname=\pgfmathresult}%
        \expandafter\expandafter\expandafter\def\expandafter\expandafter\expandafter
            \pgfmath@arguments\expandafter\expandafter\expandafter{\expandafter
                \pgfmath@arguments\expandafter{\csname pgfmath@argument@\pgfmathcounter\endcsname}}%
    \repeatpgfmathloop
    \expandafter\pgfmath@addto@toks\expandafter{\csname pgfmathfloat#1@\expandafter\endcsname\pgfmath@arguments}%
    \pgfmath@addto@toks{\pgfmathfloattofixed{\pgfmathresult}}%
    \edef\pgfmath@body{{\the\pgfmath@toks}}%
    \expandafter\pgfmath@head\pgfmath@body
}

\makeatother


\begin{document}

\begin{circuitikz}[scale=1.2, transform shape]
    \pgfkeys{/pgf/fpu/install only={reciprocal}}
    %
    % this fails with Illegal unit of measure
    %\pgfkeys{/pgf/fpu/install only={divide}} 
\draw (12,1) to [battery2, v_=$V_{cc}$] ++(0,2);
\end{circuitikz}

\end{document}