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[SPCA] more assembly

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RobinB27
2026-01-11 16:52:34 +01:00
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semester3/spca/parts/00_asm/03_operations.tex
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@@ -25,7 +25,7 @@ Arithmetic / logic operations need a size postfix (replace \texttt{X} below with
\end{tables}
\newpage
\subsubsection{Condition Codes and jumping}
\subsubsection{Condition Codes}
Any arithmetic operation (that is truly part of the arithmetic operations group, so not including \texttt{lea} for example) implicitly sets the \bi{condition codes}.
The following condition codes were covered in the lecture (operation: \texttt{t = a + b}):
\begin{itemize}
@@ -68,3 +68,16 @@ and \texttt{SF} is set if \texttt{a \& b < 0}.
\caption{Condition code postfixes for jump and set instructions}
\label{tab:condition-codes}
\end{table}
\content{Conditional Moves}
Similar to \texttt{jX}, the same postfixes can be applied to \texttt{cmovX}, for example:
\begin{minted}{gas}
cmpl %eax, %edx
cmovle %edx, %eax
\end{minted}
Will move \verb|%edx| into \verb|%eax|, only if \verb|%edx| is less or equal (\verb|le|) \verb|%eax|.
This can be used to, for example, compile ternary expressions from \verb|C| to Assembly. However, this requires evaluating both possible expressions, which may lead to a (significant) performance overhead.