How to use result of \FPeval computation "inline"?

Question

Instead of writing something as, which works

\documentclass{article}
\usepackage{array}
\usepackage{fp}    
\begin{document}

\FPeval{\result}{4*0.3} %store the result in `\result` first then:

\begin{tabular}[c]{| m{\result in}  | m{\result in} | }\hline
a&b\\\hline
\end{tabular}
\end{document}

I'd like to do the multiplication shown above, right inside the tabular environment. i.e. "inline"

But I do not know what the syntax is. It seems with \FPeval one has to do the computation first, store it in some register (called \result in the above), then later use the computed value by referencing that register again.

But I want to just to do something like \FPeval{4*0.3} and have the result be there directly. As in

\documentclass{article}
\usepackage{array}
\usepackage{fp}

\begin{document}

\begin{tabular}[c]{| m{\FPeval{}{4*0.3} in}  | m{\FPeval{}{4*0.3} in} | }\hline
a&b\\\hline
\end{tabular}
\end{document}

Which does not work. Gives syntax errors, This also does not work for some reason

\documentclass{article}
\usepackage{array}
\usepackage{fp}

\begin{document}

\begin{tabular}[c]{| m{\FPeval{\result}{4*0.3}\result in}  | m{\FPeval{\result}{4*0.3}\result in} | }\hline
a&b\\\hline
\end{tabular}
\end{document}

Is it possible to just do the multiplication "inline" directly, without having to introduce new register variables?

TL 2019

Answer 1

Use xfp instead of fp:

\documentclass{article}
\usepackage{array}
\usepackage{xfp}

\begin{document}

\begin{tabular}[c]{| m{\fpeval{4*0.3} in}  | m{\fpeval{4*0.3} in} | }\hline
a&b\\\hline
\end{tabular}
\end{document}