\resizebox{\textwidth}{!}{%
\begin{tabular}{@{}lrrrrrr@{}}
\toprule $r$ & \multicolumn{3}{c}{36 bits: iterations$/\sqrt n$} & \multicolumn{3}{c}{40 bits: iterations$/\sqrt n$} \\
 & plain & mixed 2 & mixed 4 & plain & mixed 2 & mixed 4 \\ \midrule
2 & 3.462 & --- & --- & 3.775 & --- & --- \\
3 & 2.340 & 1.775 & 2.340 & 2.262 & 1.609 & 2.262 \\
4 & 1.688 & 1.479 & 1.569 & 1.668 & 1.720 & 1.540 \\
8 & 1.341 & 1.566 & 1.351 & 1.571 & 1.471 & 1.277 \\
16 & 1.248 & 1.684 & 1.389 & 1.323 & 1.586 & 1.292 \\
20 & 1.484 & 1.479 & 1.212 & 1.531 & 1.295 & 1.226 \\
32 & 1.095 & 1.522 & 1.328 & 1.384 & 1.335 & 1.444 \\
64 & 1.369 & 1.385 & 1.577 & 1.244 & 1.432 & 1.241 \\
128 & 1.293 & 1.333 & 1.462 & 1.366 & 1.572 & 1.112 \\
\midrule
random-mapping constant $\sqrt{\pi/2}$ & 1.253 & & & 1.253 & & \\
\bottomrule
\end{tabular}}