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| author | Xiretza <xiretza@xiretza.xyz> | 2020-05-28 22:11:44 +0200 |
|---|---|---|
| committer | Xiretza <xiretza@xiretza.xyz> | 2020-05-28 22:59:04 +0200 |
| commit | f88bef767263590c94e157d0989afa91db3ccdb0 (patch) | |
| tree | 4285722060003d1c1213c0b612c3049d2a0166e9 /manual | |
| parent | c34cb90a209f609376a7a527a31925993b981011 (diff) | |
| download | yosys-f88bef767263590c94e157d0989afa91db3ccdb0.tar.gz yosys-f88bef767263590c94e157d0989afa91db3ccdb0.tar.bz2 yosys-f88bef767263590c94e157d0989afa91db3ccdb0.zip | |
Document division and modulo cells
Diffstat (limited to 'manual')
| -rw-r--r-- | manual/CHAPTER_CellLib.tex | 23 |
1 files changed, 23 insertions, 0 deletions
diff --git a/manual/CHAPTER_CellLib.tex b/manual/CHAPTER_CellLib.tex index 55abd9b96..32c530582 100644 --- a/manual/CHAPTER_CellLib.tex +++ b/manual/CHAPTER_CellLib.tex @@ -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 |