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Document division and modulo cells

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Xiretza 2020-05-28 22:11:44 +02:00
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manual/CHAPTER_CellLib.tex
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@ -139,6 +139,8 @@ Verilog & Cell Type \\
\lstinline[language=Verilog]; Y = A * B; & {\tt \$mul} \\
\lstinline[language=Verilog]; Y = A / B; & {\tt \$div} \\
\lstinline[language=Verilog]; Y = A % B; & {\tt \$mod} \\
\multicolumn{1}{c}{\tt [N/A]} & {\tt \$divfloor} \\
\multicolumn{1}{c}{\tt [N/A]} & {\tt \$modfoor} \\
\lstinline[language=Verilog]; Y = A ** B; & {\tt \$pow} \\
\end{tabular}
\caption{Cell types for binary operators with their corresponding Verilog expressions.}
@ -161,6 +163,27 @@ For the binary cells that output a logical value ({\tt \$logic\_and}, {\tt \$log
{\tt \$gt}), when the \B{Y\_WIDTH} parameter is greater than 1, the output is zero-extended,
and only the least significant bit varies.
Division and modulo cells are available in two rounding modes. The original {\tt \$div} and {\tt \$mod}
cells are based on truncating division, and correspond to the semantics of the verilog {\tt /} and
{\tt \%} operators. The {\tt \$divfloor} and {\tt \$modfloor} cells represent flooring division and
flooring modulo, the latter of which is also known as ``remainder'' in several languages. See
table~\ref{tab:CellLib_divmod} for a side-by-side comparison between the different semantics.
\begin{table}[h]
\hfil
\begin{tabular}{lr|rr|rr}
\multirow{2}{*}{Division} & \multirow{2}{*}{Result} & \multicolumn{2}{c|}{Truncating} & \multicolumn{2}{c}{Flooring} \\
& & {\tt \$div} & {\tt \$mod} & {\tt \$divfloor} & {\tt \$modfloor} \\
\hline
{\tt -10 / 3} & {\tt -3.3} & {\tt -3} & {\tt -1} & {\tt -4} & {\tt 2} \\
{\tt 10 / -3} & {\tt -3.3} & {\tt -3} & {\tt 1} & {\tt -4} & {\tt -2} \\
{\tt -10 / -3} & {\tt 3.3} & {\tt 3} & {\tt -1} & {\tt 3} & {\tt -1} \\
{\tt 10 / 3} & {\tt 3.3} & {\tt 3} & {\tt 1} & {\tt 3} & {\tt 1} \\
\end{tabular}
\caption{Comparison between different rounding modes for division and modulo cells.}
\label{tab:CellLib_divmod}
\end{table}
\subsection{Multiplexers}
Multiplexers are generated by the Verilog HDL frontend for {\tt